THAT THEULTITUTO US009759838B2

(12) United States Patent (10) Patent No.: US 9 ,759,838 B2

Thompson et al. (45 ) Date of Patent: Sep. 12, 2017
(54 ) CORRELATION TECHNIQUES FOR (58 ) Field of Classification Search
PASSIVE ELECTROSEISMIC AND CPC . GO1V 1/28 ; GOLV 1 /30 ; G01V 11/00 ; G01V
SEISMOELECTRIC SURVEYING 1/ 364; GOLV 1/42
See application file for complete search history .
( 71 ) Applicant: Hunt Energy Enterprises, L .L . C .,
Dallas, TX (US) (56 ) References Cited
(72) Inventors : Arthur Thompson , Houston, TX (US ); U . S. PATENT DOCUMENTS
Alan Katz , Dallas , TX (US ); Robert
England, Flower Mound , TX (US ); 4 , 507 ,611 A 3 / 1985 Helms
Mohammad Rahman , Dallas , TX 4 ,573 ,148 A 2 / 1986 Herkenhoff et al.
(US) ; Naga P . Devineni, Irving , TX 4 ,686 ,475 A 8/ 1987 Kober et al.
(US) (Continued )
(73) Assignee : ES XPLORE , L .L .C ., Dallas, TX (US ) FOREIGN PATENT DOCUMENTS
GB 2 459 365 10 /2009
( * ) Notice : Subject to any disclaimer, the term of this WO WO 2010 /080366 12 / 2009
patent is extended or adjusted under 35
U . S . C . 154( b ) by 340 days. OTHER PUBLICATIONS
(21) Appl. No.: 14 /515,271 International Search Report and Written Opinion issued in related
PCT Application No. PCT/US2014 /019439 mailed Dec. 15 , 2014 ,
(22) Filed: Oct. 15, 2014 12 pages.
(65 ) Prior Publication Data ( Continued )
US 2015 /0071033 A1 Mar. 12 , 2015 Primary Examiner — Hovhannes Baghdasaryan
Related U .S. Application Data (74 ) Attorney, Agent, or Firm — Baker Botts L .L .P.
(63) Continuation of application No. 13/785,106 , filed on (57) ABSTRACT
Mar. 5 , 2013, now Pat. No. 8 ,873, 334 .
A method for surveying, may include receiving , by a pro
(51) Int . CI. cessor, first survey data from a first source , the first source
GOIV 1 /28 (2006 .01) comprising a first signal generated by a subsurface earth
GOIV 11/00 (2006 .01) formation in response to a passive -source electromagnetic
GOIV 136 (2006 .01) signal, wherein the electromagnetic signal is generated by an
GOIV 138 ( 2006 .01) electroseismic or seismoelectric conversion of the passive
(Continued ) source electromagnetic signal. Themethod may also include
(52 ) U .S . CI. receiving , by the processor, second survey data from a
CPC .............. GOIV 11 /007 ( 2013 .01 ) ; GOIV 1/28 second source and processing the first survey data and the
( 2013 . 01); GOIV 1/ 36 (2013 .01); GOIV 1 /364 second survey data to determine one or more properties of
(2013 .01); GOIV 1/38 ( 2013 .01); GOIV 1/ 42 a subsurface earth formation .
(2013.01 ); GOLV 1/48 (2013 .01 ); GOIV 11/00
(2013 .01) 20 Claims, 11 Drawing Sheets

400

206 280
26b

12 260 286
28b
28 - V A 42
209944
 US 9, 759,838 B2
Page 2

(51) Int. Ci. 2007/0294036 Al 12/2007 Strack et al.

GOIV 1/48 ( 2006 .01) 2009/0108845 Al 4 /2009 Kaminski
GOIV 1/42 ( 2006 .01) 2010 / 0225324 A1 9 /2010 Strack et al.
2013 /0066561 A1 3 /2013 Thompson et al.
2013/0069654 Al 3 /2013 Thompson et al .
(56) References Cited 2013/0070562 Al
2013 /0073210 A1
3 / 2013 Thompson et al.
3 /2013 Thompson et al.
U . S . PATENT DOCUMENTS 2013 /01 19993 A1 5 /2013 Thompson et al.
4 ,825, 165 A 4 / 1989 Helms et al.
4 ,841,250 A 6 / 1989 Jackson OTHER PUBLICATIONS
4 ,904 , 942 A 2 / 1990 Thompson
4 , 964,098 A 10 / 1990 Hornbostel U .S . Appl. No. 61/469 ,498 , filed Mar. 30 , 2011 , Arthur Thompson.
5 ,041 ,792 A 8 / 1991 Thompson PCT Notification of Transmittal of the International Search Report
H1490 H 9 / 1995 Thompson et al. and the Written Opinion of the International Searching Authoritiy of
5 , 486 ,764 A 1/ 1996 Thompson et al . the Declaration ; Int'l application No. PCT/US2012 /030750 ; 25
H1524 H 4 / 1996 Thompson et al. pages, Sep . 18 , 2012 .
H1561 H 7 / 1996 Thompson
5 , 777 ,478 A 7 / 1998 Jackson Simpson , Fiona , et al.; “ Practical Magnetotellurics,” Feb . 15, 2005,
5 , 877 ,995 A 3/ 1999 Thompson et al. Cambridge University Press , Feb . 14 , 2005 .
6 ,462,549 B1 10 / 2002 Curtis et al . European Search Report; European Patent Application No .
6, 476, 608 B1 . 11 /2002 Dong 12161617 . 1 .- 2213 ; dated Jul. 4 , 2012 , 6 pages, Jul. 4 , 2012 .
6 ,477,113 B2 . 11/ 2002 Hornbostel et al. U . S . Appl. No. 61/528 ,421, Aug. 29 , 2011 , Alan Katz .
6 ,664 ,788 B2 12 / 2003 Hornbostel et al. H . Roder, et al.; “ Seismo -electrical effects : Experiments and Field
6 , 950,747 B2 9/ 2005 Byerly Measurements ;" Applied Physics Letters, AIP , American Institute of
7,248, 052 B2 7 /2007 Weaver et al. Physics , Melville , NY, US , vol. 80 , No. 2; XP012030927 ; pp .
7 ,330,790 B2 2 /2008 Berg 334 - 336 , Jan . 14 , 2002 .
7 ,340,348 B2 3 / 2008 Strack et al. Arthur Thompson et al., Patent Application entitled “Method and
7 ,397, 417 B2 7 / 2008 Jackson System for Passive Electroseismic Surveying ” and Preliminary
7 ,573, 780 B2 8 / 2009 Thompson et al.
8 ,169 ,222 B2 5 /2012 Hornbostel et al. Amendment, U .S . Appl. No. 13/712 , 177 , filed Dec . 12 , 2012 , 146
8, 347, 658 B2 1/2013 Thompson et al . pages.
2002 /0181326 Al 12 / 2002 Hornbostel et al. Robert England et al., Patent Application entitled , “ Sensors for
2006 /0132137 A1 6 /2006 MacGregor et al. Passive Electroseismic and Seismoelectric Surveying" U .S . Appl.
2007/ 0257830 AL 11/ 2007 Savage et al. No. 13 /785 ,372 , filed Mar. 5 , 2013 , 91 pages.
U . S . Patent Sep. 12 , 2017 Sheet 1 of 11 US 9 ,759,838 B2

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U . S . Patent Sep . 12 , 2017 Sheet 2 of 11 US 9 ,759, 838 B2

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U . S . Patent Sep. 12 , 2017 Sheet 3 of 11 US 9,759,838 B2

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U . S . Patent Sep . 12 , 2017 Sheet 4 of 11 US 9 ,759 ,838 B2

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U . S . Patent Sep. 12 , 2017 Sheet 5 of 11 US 9 ,759,838 B2

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U . S . Patent Sep. 12 , 2017 Sheet 6 of 11 US 9 ,759,838 B2

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U . S . Patent Sep. 12 , 2017 Sheet 7 of 11 US 9, 759 ,838 B2

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U . S . Patent Sep. 12 , 2017 Sheet 8 of 11 US 9 ,759 ,838 B2

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U . S . Patent Sep. 12 , 2017 Sheet 9 of 11 US 9 ,759,838 B2

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U . S . Patent Sep . 12 , 2017 Sheet 10 of 11 US 9,759,838 B2

800

RECEIVE FIRST SIGNAL FROM FIRST SENSOR

802
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812
CORRELATE RECEIVED SIGNALS
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DETERMINE SUBSURFACE EARTH FORMATION
PROPERTIES

END
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U . S . Patent Sep. 12 , 2017 Sheet 11 of 11 US 9,759,838 B2

980 10
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 US 9 ,759, 838 B2
CORRELATION TECHNIQUES FOR response to an electroseismic or seismoelectric conversion
PASSIVE ELECTROSEISMIC AND of the earth 's background electric field . The electroseismic
SEISMOELECTRIC SURVEYING or seismoelectric conversion may take place in a subsurface
earth formation . The detected electromagnetic signal may be
RELATED APPLICATION 5 a vertical signal that is responsive to a vertical component of
the earth 's background electric field . Another technical
This application is a continuation of U . S . application Ser. advantage may be the ability to detect a seismic signal
No. 13 /785 , 106 filed Mar . 5 , 2013 and entitled “ Correlation generated in response to an electroseismic or seismoelectric
Techniques for Passive Electroseismic and Seismoelectric conversion of the earth ' s background electric field . Using
Surveying” . such techniques, geophysical surveying may be performed
BACKGROUND OF THE INVENTION without the requirement for expensive active sources of
electromagnetic or seismic energy, which may improve site
Conventional geophysical surveying techniques rely on insafety the
and reduce any environmental impacts . The reduction
amount of equipment and power, along with the
various surveying technologies to identify prospective 15 corresponding reduced footprint at the measurement site ,
regions for drilling or exploration . These conventional sur
veying technologies , however, suffer from certain limita may be an advantage over other surveying systems and
methods. From an environmental and health perspective , the
tions that may prevent a full understanding of the geophysi
cal properties of prospective regions. For example, reduction in transportation, site preparation , and high energy
particular surveying techniques may require the use of 20 sources may improve the overall health and safety of the
expensive and /or time consuming surveying equipment and workers operating the equipment. In addition , the earth 's
methods that may limit the economic viability ofsurveying naturally occurring electromagnetic field comprises a broad
a particular prospective region . In addition , particular sur spectrum of frequencies, from sub- hertz frequencies to tens
veying technologies may be able to provide information of thousands of hertz frequencies, along with a broad
regarding one or more geophysical properties of a subsur - 25 coverage over the surface of the earth . This broad spectrum
face region , but may not be able to provide information on allows for a broad range of penetration depths from tens of
other geophysical properties. Such limitations may lead to meters to tens of kilometers . Accordingly, the electromag
the identification of prospective regions for drilling or netic and /or seismic signals detected may be processed to
exploration based on an incomplete and/ or incorrect under - identify various properties of the subsurface earth formation .
standing of the prospective region , which may cause unnec - 30 Another technical advantage may include the ability to
essary time and /or expenses to be incurred exploring or utilize survey data from passive electroseismic or seismo
drilling regions that do not have the desired geophysical electric surveying and survey data from other geophysical
properties. For example , based on incomplete or incorrect surveying methods to determine one or more properties of a
geophysical surveying, a drilling operation may drill a dry subsurface earth formation . For example , the data from the
hole or drill into a subsurface formation that holds fewer 35 first survey method may be correlated to the data from the
hydrocarbons than expected . As another example , an explo second survey method . Utilizing data from two or more
ration company may miscalculate the estimated amount of survey methods may allow for a more complete and / or
reserves in a subsurface formation . reliable understanding of the subsurface formation of inter
est .
SUMMARY Other technical advantages of the present disclosure will
be readily apparent to one of ordinary skill in the art from the
In accordance with the teachings of the present disclosure , following figures, description , and claims. Moreover, other
disadvantages and problems associated with conventional specific advantages of particular surveying techniques and
geophysical surveying techniques may be reduced and/or combinations are discussed below .Moreover , while specific
eliminated . For example , a surveying system may be pro - 45 advantages are explained in the present disclosure , various
vided using passive electroseismic or seismoelectric survey - embodiments may include some, all , or none of those
ing techniques. The surveying system may utilize survey advantages.
data from passive electroseismic or seismoelectric surveying
and survey data from other geophysical surveying methods BRIEF DESCRIPTION OF THE DRAWINGS
to determine one or more properties of a subsurface earth 50
formation . For a more complete understanding of the present inven
In accordance with one embodiment of the present dis tion and its features and advantages, reference is now made
closure , a method for surveying , may include receiving, by to the following description , taken in conjunction with the
a processor, first survey data from a first source, the first accompanying drawings, in which :
source comprising a first signal generated by a subsurface 55 FIG . 1A is a perspective diagram illustrating an example
earth formation in response to a passive - source electromag - system for passive electroseismic and seismoelectric sur
netic signal, wherein the electromagnetic signal is generated veying ;
by an electroseismic or seismoelectric conversion of the FIG . 1B is a perspective diagram illustrating an example
passive - source electromagnetic signal. Themethod may also system for passive electroseismic and seismoelectric sur
include receiving, by the processor, second survey data from 60 veying ;
a second source and processing the first survey data and the FIGS. 2A - 2C are block diagrams illustrating example
second survey data to determine one or more properties of sensors for passive electroseismic and seismoelectric sur
a subsurface earth formation . veying ;
Technical advantages of certain embodiments of the pres FIG . 3 is a flowchart illustrating an example method for
ent invention include the ability to perform passive electro - 65 processing two or more sources of geophysical survey data ;
seismic or seismoelectric surveying. Such surveying may be FIG . 4 is a perspective diagram illustrating an example
able to detect an electromagnetic signal generated in surveying system utilizing passive electroseismic and seis
 US 9 ,759,838 B2
moelectric surveying techniques, active electroseismic and active source . Passive surveying may detect the generation
seismoelectric surveying techniques, and active seismic of secondary seismic waves through coupling of the elec
surveying techniques; tromagnetic source field to various rock formations (elec
FIG . 5 is a perspective drawing illustrating an example troseismic effect) and subsequent generations of secondary
surveying system utilizing passive electroseismic and seis- 5 electromagnetic fields through coupling of the generated
moelectric surveying techniques and controlled source elec seismic waves with various rock formations (seismoelectric
tromagnetic surveying techniques;
FIG . 6 is a perspective drawing illustrating an example effect ) to probe those formations and the fluids they contain .
Alternatively or in addition , passive surveying may detect
surveying system utilizing passive electroseismic and seis the generation of secondary electromagnetic fields through
moelectric surveying techniques and magnetotelluric sur - 10" coupling of a seismic source field to various rock formations
veying techniques ;
FIG . 7 is a perspective drawing illustrating an example (ondary
seismoelectric effect ) and subsequent generations of sec
seismic waves through coupling of the generated
surveying system utilizing passive electroseismic and seis electromagnetic fields with various rock formations ( elec
moelectric
m surveying techniques and logging techniques ; troseismic effect) to probe those formations and the fluids
FIG . 8 is a flowchart illustrating an example method for 15 they contain . Generation of tertiary and higher order elec
correlating data received from various geophysical survey tromagnetic fields and seismic waves can also result from
methods ; and
FIG . 9 is a block diagram illustrating an example com additional couplings as the fields propagate towards the
puter system suitable for implementing one or more embodi surface of the earth .
ments disclosed herein . 20 Other surveying techniques such as magnetotelluric sur
veying or controlled -source electroseismic surveying typi
DESCRIPTION OF EXAMPLE EMBODIMENTS cally reject signals generated by such passively -generated
conversions as background noise . Utilizing the teachings of
The example embodiments herein may utilize passive the present disclosure , however, electromagnetic and seis
surveying techniques that utilize passive sources, such as 25 mic signals generated by seismoelectric and electroseismic
naturally occurring electromagnetic fields and /or seismic conversions in response to a passive source of energy may
waves, and the interactions of electromagnetic or seismic be detected and processed using various data processing
signals generated by those sources with subsurface forma- techniques to identify properties of the subsurface earth
tions through electroseismic and/ or seismoelectric conver - formation . For example , a generated seismic signal may be
sions to identify features and / or properties of subsurface 30 identified by detecting the characteristic time lags or fre
earth formations. Such surveying may be useful for a variety quencies associated with the seismic travel time using a
of purposes , including the identification of subsurface water time- selective method and determining the depth of origin of
and minerals . While passive surveying may be suitable for the seismic signal from said time selective method .
use as a standalone method of geophysical surveying , pas Electromagnetic and /or seismic signals generated as a
sive surveying may , in some embodiments , be performed in 35 result of electroseismic or seismoelectric conversions may
conjunction with other geophysical surveying methods to be detected in any appropriate manner. For example , various
identify properties of subsurface earth formations . The sensors may be utilized to detect one or more of an elec
teachings of the present disclosure are intended to encom - tromagnetic signal and a seismic signal that are generated by
pass embodiments that employ passive surveying as a stand a subsurface earth formation in response to a passive-source
alone surveying technique as well as embodiments that use 40 electromagnetic or seismic signal, wherein the electromag
passive surveying in conjunction with one or more other netic signal is generated by an electroseismic or seismoelec
methods of geophysical surveying. tric conversion of the passive -source electromagnetic or
A passive source may be utilized to provide the energy for seismic signal. In some embodiments , arrays of sensors may
generating electroseismic and/or seismoelectric conversions be utilized . Data processing may be utilized to process
in a subsurface formation or structural feature. For example , 45 signals to facilitate identification of one or more of the
the earth ' s electromagnetic field and/ or environmental seis - subsurface earth formation properties discussed above.
mic energy may induce electroseismic or seismoelectric Using these techniques, various properties of the subsur
conversions in a subsurface earth formation that holds face earth formation may be identified . For example , pro
hydrocarbons or other minerals . As used herein , a " passive cessing the detected signal may indicate the presence of
source ” may include any source that is not being actively 50 fluids such as hydrocarbons and aqueous fluid such as
initiated by a surveying operation to actively generate a potable water, fresh water, and brine water in the subterra
source ofseismic and/ or electromagnetic energy . Although a nean formation . In some embodiments, the teachings of the
passive source generally includes a natural source of elec - present disclosure may be utilized to identify additional
tromagnetic energy and /or seismic energy such as the earth 's properties of the subsurface earth formation , including but
natural electromagnetic field , other man -made sources of 55 not limited to the existence of the subsurface earth forma
electromagnetic and/ or seismic radiation such as electrical tion , depth of the subsurface formation , porosity and /or fluid
power lines or mechanical equipment may also be included permeability of the subsurface earth formation , the compo
as passive sources in particular embodiments . While certain sition of one or more fluids within the subsurface earth
man -made sources may induce an electromagnetic field or formation , a spatial extent of the subsurface earth formation ,
seismic wave, they are distinguishable from an " active 60 an orientation of the boundaries of the subsurface earth
source ” such as a seismic generator, explosives, electric field formation , and resistivity of the subsurface earth formation .
generators , and the like in that such sources are generally Based on the identified properties , models may be developed
initiated by and / or are associated with a surveying operation of the subsurface earth formation , including three -dimen
to facilitate surveying a subterranean formation . As used sional and structures and time-dependent models. In addi
herein , " passive surveying," " passive electroseismic survey - 65 tion or in the alternative, the techniques of the present
ing," and " passive seismoelectric surveying" may refer to disclosure may be utilized to identify the presence of and/ or
surveying that utilizes a passive source as opposed to an migration of various pollutants, flooding in hydrocarbon
 US 9, 759,838 B2
production , fault movement, aquifer depth , water use , the generated as a result of a seismoelectric conversion as
presence of and/ormigration ofmagma, and hydrofracturing seismic signals 20a propagate towards the surface. Electro
properties. magnetic sensors 26 may detect electromagnetic signals 22 .
In some embodiments , passive survey data obtained and Seismic sensors 28 may detect seismic signals 20b .
or collected as a result of passive surveying may be pro - 5 Passive electromagnetic source 12 may represent earth ' s
cessed with geophysical survey data obtained and /or col- naturally occurring electromagnetic field . Earth 's naturally
lected using various other surveying techniques. Processing occurring electromagnetic field may include a broad spec
passive survey data and other available sources of geophysi trum of frequencies , from sub -hertz frequencies to tens of
cal survey data may provide various technical benefits . For thousands of hertz frequencies, having a broad coverage
example , such processing may allow additional information , 10 over the surface of the earth . This broad spectrum allows for
more complete information , and /or confirmation of infor - a broad range of penetration depths of electromagnetic
mation regarding subsurface earth formations . Such process - signal 14 from tens of meters to tens of kilometers. The
ing may take advantage of particular strengths of other corresponding frequencies of electromagnetic signal 14 in
survey methods to establish a baseline for comparison the earth may result from variations in passive electromag
and / or determine particular properties for which those meth - 15 netic source 12 due to various natural events such as
ods are well-suited . As a result, passive surveying tech - electromagnetic fluctuations in the ionosphere , naturally
niques combined with other available surveying techniques occurring electromagnetic discharges in the atmosphere
may result in a more complete understanding of the subsur - such as lightning, and /or other electromagnetic events. In
face formation than would otherwise have been available if some embodiments, passive electromagnetic source 12 of
the individual techniques were used alone . 20 electromagnetic signals 14 may include cultural sources of
While specific advantages have been enumerated above , electromagnetic radiation , which may have sufficiently low
various embodiments may include all, some, or none of the frequencies to reach and interact with subterranean forma
enumerated advantages . Embodiments of the present disclo - tion 16 . As another example , passive electromagnetic source
sure and its advantages are best understood by referring to 12 may include power transmission lines, which may gen
FIGS. 1 through 9 , wherein like numerals refer to like and 25 erate electromagnetic signals 14 of appropriate strength
corresponding parts of the various drawings. and / or frequency to interact with subterranean formation 16 .
FIGS . 1A and 1B are perspective diagrams illustrating an Electromagnetic signal 14 represents an electromagnetic
example system 10 for passive electroseismic and seismo - wave , electromagnetic plane wave, or other appropriate
electric surveying. System 10 includes electromagnetic sen - electromagnetic signal that propagates into the Earth from
sors 26 , seismic sensors 28 , and computing system 30 . FIG . 30 passive electromagnetic source 12 . For example , in response
1A illustrates an embodiment in which system 10 is gener - to Earth ' s electromagnetic field , electromagnetic signal 14
ally configured to utilize signals 14 propagated by a passive may propagate into the Earth as an electromagnetic modu
electromagnetic source 12 of electromagnetic energy to lation that, unlike an acoustic wave , travels at the speed of
perform geophysical surveying. FIG . 1B illustrates an an electromagnetic wave in the subsurface . The speed of an
embodiment in which system 10 is generally configured to 35 electromagnetic wave in the subsurface may generally be
utilize signals 20 and /or 22 , which may be propagated by a less than the speed of an electromagnetic wave in a vacuum
passive seismic source 40 . or air . Electromagnetic signal 14 may typically travel in the
As illustrated in FIG . 1A , sensors 26 and/or 28 generally subsurface of the earth at a speed of about one hundred times
detect signals generated by subsurface earth formation 16 in greater than the speed of propagation of an acoustic wave in
response to a electromagnetic signal 14 propagated from 40 the seismic frequency band of about 1 - 100 Hz. Due to the
passive electromagnetic source 12 . Computing system 30 relative speed of electromagnetic signal 14 when compared
may then process detected signals using various signal to a seismic signal, the travel time of the electromagnetic
processing techniques to identify properties and / or features signal 14 into the subsurface earth formation may, in some
of subsurface earth formation 16 . System 10 may detect embodiments , be ignored when processing the detected
seismic signals 20 generated due to the electroseismic 45 electromagnetic field 22 and /or detected seismic signals 20 .
interactions between the electromagnetic signal 14 and the Although illustrated as a static field , it should be noted that
subsurface formation 16 , either alone or in combination with electromagnetic signal 14 may be a time- varying field .
detecting electromagnetic signal 22 , which may be gener - Electromagnetic signal 14 may propagate into the sub
ated as a result of seismoelectric conversions of seismic surface of the earth as an approximate plane wave, including
signals 20 . One or more of the detected signals may then be 50 over subsurface formation 16 of interest. The term " plane
processed to determine one or more properties of the sub wave ” may refer to a wave with a substantially uniform
surface earth formation . amplitude on a plane normal to a velocity vector of elec
Passive electromagnetic source 12 represents any appro - tromagnetic signal 14 . The velocity vector may be generally
priate passive source of electromagnetic energy . For vertical, although not necessarily perpendicular to the sur
example , passive electromagnetic source 12 may represent 55 face of the Earth above subsurface earth formation 16 . For
the earth ' s natural electromagnetic field . Passive electro - example , a velocity vector may be substantially verticalbut
magnetic source 12 propagates electromagnetic energy into may appear inclined relative to a vertical axis at the surface
the subsurface of the earth as electromagnetic signal 14 . where the surface is on an incline, such as on a hillside or
Electromagnetic signal 14 may represent, for example , an o ther incline . As a result of the electroseismic effect and /or
electromagnetic plane wave 14 . As electromagnetic signal 60 seismoelectric effect , the seismic signals 20 and/ or electro
14 propagates into the earth , it may encounter various magnetic signals 22 resulting from electromagnetic signals
subsurface earth formations 16 . The interaction of electro - 14 may be generated substantially uniformly across subsur
magnetic signal 14 and subsurface earth formation 16 may face formation 16 . As a result , seismic signals 20 and/or
cause an electroseismic conversion to take place at an edge electromagnetic signals 22 may each form a substantially
and /or boundary 18 of subsurface formation 16 . As a result, 65 vertical plane wave traveling to the surface of the Earth .
one or more seismic waves 20 may propagate towards the Subsurface earth formation 16 represents any subsurface
surface of the earth . Electromagnetic signal 22 may be earth formation of interest for the purposes of geophysical
 US 9 ,759,838 B2
surveying . Subsurface earth formation 16 may represent a electroseismic energy conversion may occur at the boundary
geologic formation that holds one or more fluids. In some 18 between reservoir rock and the sealing and/or confining
embodiments, subsurface earth formation 16 represents a rock . Alternatively , electroseismic energy conversion may
porous rock formation able to hold fluids. A porous rock occur at an interface 18 between pore fluids, for example ,
formation may , for example , include solid rock portion 5 between oil and water . At the rock and /or fluid interfaces 18
interspersed with channel-like porous spaces. A porous rock there may be a gradient in the chemical potential. For
formation may, for example , include an earth substance example , at the boundary 18 between a silicate rock and a
containing non - earthen volume or pore space , and may carbonate rock , a chemical reaction may occur in the com
include , but is not limited to , consolidated , poorly consoli - mingled pore fluids . For example , the silicate may dissolve
dated , or unconsolidated earthen materials. Fluids held by 10 the carbonate , and the silicate ions in solution may react with
subsurface earth formation 16 may be hydrocarbons such as the carbonate ions in solution . The overall reaction may be
oil and gas, water (including fresh , salt , potable, or briny driven by a gradient in the chemical potential at the interface
water ) , helium , carbon dioxide , minerals , or other earth 18 . The reaction product between positive and negative ions
fluids. In some embodiments, subsurface earth formation 16 in solution is electrically neutral and may precipitate out of
may represent a formation holding pollutants , magma, or 15 solution . When a precipitate is formed , the resulting depo
molten material. Subsurface earth formation 16 may repre - sition of the precipitate strengthens the rock , increases its
sent a geologic layer, a stratographic trap , a fault, a fold - hardness , and increases the electrical resistivity of the inter
thrust belt , or other geographic formation of interest . Sub - face . During the reactions in pore spaces, concentration
surface earth formation 16 may represent a prospective or gradients of charged ions may be created within the pore
potential area of interest for exploration and /or drilling 20 fluids. These concentration gradients may produce an elec
operations . trochemical-potential gradient which may manifest itself as
Subsurface earth formation 16 may include a polarizable a macroscopic electrical potential gradient. The internal
fluid including one ormore fluid dipoles 114 associated with electrical potential gradients at the interfaces may create
a fluid in subsurface earth formation 16 . As a result, an internal stresses, and the interaction of the earth 's back
electrochemical interaction may form between the polariz - 25 ground electromagnetic field 14 with the electrochemical
able fluid and the solid rock portions at boundary 18 . The potential gradient may change these internal stresses . Due to
electrochemical interaction is represented by the “ +” symbol the natural modulations in the earth 's background electro
in the fluid portion and the “ _ ” symbol in the solid rock magnetic field 14 , the internal stresses may be modulated ,
portion . Electromagnetic signals 14 may encounter and/ or accounting for the nonlinear electroseismic conversions that
interact with fluid dipoles 114 of subsurface earth formation 30 may be measured and used by system 10 .
16 . In particular, the electromagnetic signals 14 may cause Seismic signals 20 represent any seismic signals and / or
a change in the polarization of dipoles 114 in the pore fluid , seismic waves generated by the electroseismic effect in
which in turn may cause a pressure pulse 118 to be gener - response to electromagnetic signal 14 . As noted above,
ated . For example , electromagnetic signals 14 may modify seismic signals 20 may represent a substantially vertical
the electrochemical bonds or move the charges of fluid 35 plane wave that travels towards the surface of the Earth .
dipoles 114 , thereby effectively creating pressure pulse 118 Seismic signals 20 may generate subsequent secondary
where the interactions are distorted . Pressure pulse 118 may electromagnetic fields and seismic waves through various
represent a change in pressure and /or fluid flow that pro - combinations of the electroseismic and seismoelectric
duces a time- varying pressure gradient, which may then effects as seismic signals 20 propagate to the surface . For
propagate and / or be transmitted into the earth formation (or 40 example , as illustrated , seismic wave 20a may be converted
rock ) at boundary 18 of subsurface earth formation 16 . by the seismoelectric effect to an electromagnetic signal 22
Electromagnetic signals 14 exist throughout the fluid area at a near surface formation 24 . In some embodiments ,
and may primarily affect the charges of the dipoles 114 seismic signals 20 may represent secondary seismic signals
which are at or near boundary 18 of the rock . The pressure generated as a result of various seismoelectric and/or elec
gradient produced by pressure pulse 118 may propagate 45 troseismic conversions of seismic signals 20 as they propa
towards the surface as seismic signal 20 . In should be noted gate towards the surface. Seismic signals 20 may represent
that the solid rock portion may have an existing natural any mechanical seismic wave that propagates in the subsur
surface charge over at least a portion of the rock surface . The face of the earth and may include , but is not limited to , P
electrochemical interaction may result in a local pore fluid and S -waves .
dipole 114 that causes a local background electromagnetic 50 Electromagnetic signals 22 represent any electromagnetic
field . Moreover, the sign of the background electromagnetic signals , electromagnetic fields, or electromagnetic waves
field or field polarity direction depends on the surface charge generated by the seismoelectric effect in response to seismic
on the solid and the way the fluid screens out that charge . For signals 20 . As noted above , electromagnetic signals 22 may
example , for clay layers, the charge is typically as shown as represent a substantially vertical plane wave traveling to the
illustrated . In other materials such as carbonates , however, 55 surface of the Earth . Electromagnetic signals 22 may gen
the charge may be reversed . Thus , an appropriate subsurface erate subsequent secondary seismic signals and electromag
formation 16 may be a subsurface source of seismic energy . netic signals as electromagnetic signals 22 propagate to the
Boundary 18 may represent an appropriate edge , bound
nd . surface. Electromagnetic signals 22 may represent second
ary , fluid surface, or interface between subsurface earth ary electromagnetic signals generated as a result of various
formation 16 and other portions of the subsurface . Boundary 60 seismoelectric and / or electroseismic conversions of seismic
18 may represent the boundary of a hydrocarbon reservoir , signals 20 as they propagate towards the surface . In some
stratographic trap , fold thrust belt , geologic rock layer, or embodiments, electromagnetic signals 22 may be detectable
other geological formation holding or likely to hold fluids in the near-surface of the Earth and/or at some distance
and other minerals of interest. Boundary 18 may represent a above the surface of the Earth . In addition , electromagnetic
boundary between any two types of subsurface materials . 65 signals 22 may represent a time- variant electromagnetic
Electroseismic energy conversion may occur at the field resulting from the seismoelectric effect. Electromag
boundary 18 between two types of rock . For example , the netic signals 22 may modulate an electromagnetic field
 US 9, 759,838 B2
within the Earth , such as in the near surface 24 and may thus above the surface of the earth as a detectable electromag
be referred to as a modulating signal. “ Modulation ,” or netic field. It should also be noted that an electromagnetic
“ modulating,” may refer to frequency modulation , phase field generally includes an electric field and a magnetic field .
modulation , and /or amplitude modulation . For example, Accordingly , electromagnetic sensor 26 may be capable of
seismic signals 20 may travel to the near -surface 24 and 5 detecting electromagnetic signals 22 , an electric portion of
directly modulate an electromagnetic field within the near - electromagnetic signals 22, and / or a magnetic portion of
surface 24 . Seismic signals 20 may cause a change in the electromagnetic signals 22 . In some embodiments , electro
electrical impedance in near- surface 24 , which may result in magnetic sensor 26 may represent a magnetic field detector
a time-dependent variation of electromagnetic signals 22 capable of detecting a magnetic field . In some embodiments ,
and / or the passage of seismic signals 20 may interact with a 10 electromagnetic sensors 26 may be configured to attenuate
fluid or rock boundary at near surface 20 to produce elec - and /or reject horizontal electromagnetic signals .
tromagnetic signals 20 . Electromagnetic sensors 26 may be arranged in an array
Electroseismic conversions may also produce nonlinear and /or in a variety of patterns. Any appropriate number of
electromagnetic conversions. Seismoelectric and electro electromagnetic sensors 26 may be arranged in the array or
seismic effects generate harmonic responses where the cou - 15 pattern . For example , an array of electromagnetic sensors 26
pling of electromagnetic signals 22 and seismic signals 20 may include anywhere from two to thousands of sensors . In
create new modulations at frequencies that are harmonics of some embodiments , electromagnetic sensors 26 may repre
the electromagnetic signals 22 and seismic signals 20 . sent a set of sensors that includes one or more magnetic field
Accordingly , electromagnetic signals 22 and seismic signals detectors, one or more electric field detectors , and one or
20 may represent one or more non -linear electromagnetic 20 more electromagnetic field detectors, which may be used in
responses . Nonlinear electroseismic conversions may pro - particular locations for passive surveying. The array may be
duce signals useful during processing. In some embodi- configured to dispose electromagnetic sensors , such as sen
ments, nonlinear, harmonic signals having frequency com - sor 26a and 26b , separated by any appropriate lateral dis
ponents at higher frequency harmonics of the passive tance . For example, sensor 26a and 26b may be located
electromagnetic source 12 ' s fundamental frequency , such as 25 anywhere between several inches to several miles apart .
those frequencies present in the earth ' s background electro - Sensors 26 may comprise any type of sensor capable of
magnetic field , may be detected as a result of distortions of measuring the vertical electric field component of electro
electromagnetic signals 14 interacting with subsurface earth magnetic signals 22 in the near surface 24 of the Earth . In
formation 16 when it contains at least one fluid . The some embodiments , additional or alternative signals may
harmonic signals may be processed alone or in conjunction 30 also be measured including the background vertical portion
with the fundamental frequencies of the seismic signals 20 of electromagnetic signals 14 , the passive electromagnetic
and /or the electromagnetic signals 22 to determine one or source 12 of electromagnetic radiation , one or more com
more properties of the subsurface earth formation . In some ponents of the magnetic field , one or more horizontal
embodiments , system 10 may be utilized to detect and /or components of the electromagnetic signal and /or one or
isolate the harmonic signals that may be present in both 35 more components of the seismic amplitude . In some
electromagnetic signals 22 and seismic signals 20 . embodiments , one or more electromagnetic field detectors
Subsurface formation 16 may generate seismic signals 20 may be configured to measure a horizontal component ofthe
and /or electromagnetic signals 22 particularly when fluid is earth 's electromagnetic field in one or more dimensions. For
present in a porous formation , such as formations of high example , sensors 26 may include electrode pairs disposed in
permeability. Accordingly, seismic signals 20 and/or elec - 40 a horizontal alignment to measure one or more horizontal
tromagnetic signals 22 may indicate the presence of that components of electromagnetic signals 22 and/ or electro
fluid and/ or may be utilized by system 10 to locate and/ or magnetic signals 14 . In some embodiments, sensor 26 may
potentially locate particular fluids, such as hydrocarbons , be configured to measure multiple components of electro
water, or other types of fluids as described above . In magnetic signals 22 and /or 14 . For example, sensor 26 may
addition , when conventional seismic reflection boundaries 45 represent a two - axis electromagnetic field detector and /or a
18 exist between subsurface formation 16 and the surface , three - axis electromagnetic field detector.
seismic reflections may occur and may be detected by Sensors 26 may be disposed above the surface ofthe Earth
seismic sensors 20 . and /or within the Earth . In some embodiments , sensor 26
Near - surface formation 24 represents a subsurface forma- may be placed at or on the surface of the Earth or at any
tion at or near the surface of the Earth . Near -surface forma- 50 distance above the surface of the Earth . For example ,
tion 24 may , for example , represent a water table or other electromagnetic sensors 26 may be disposed anywhere from
porous rock layer . Seismic signals 20 may interact with fluid one to one hundred feet above the Earth , depending on the
in pores of near -surface formation 24 . As a result, charges relative amplification capabilities of sensors 26 and the
within the pore may be modified . The pore may, for attenuation of electromagnetic signals 22. In some embodi
example , contain fresh water as is present in the water table . 55 ments , sensors 26 may be disposed above and /or below the
The resulting modification of the charges may generate an water table , above and/ or below subsurface earth formation
alternating current field , which may lead to the emission of 16 , and/ or any appropriate combinations of locations and
electromagnetic signals 22 through the seismoelectric effect. depths. Sensors 26 may be maintained in one location during
Electromagnetic sensors 26 represent any suitable com - a detection period of particular electromagnetic signals 22
bination of sensing elements capable of detecting and /or 60 and /or may be subsequently moved to provide another
measuring at least some portion of electromagnetic signals detection period . Additionally or alternatively , a plurality of
22 . Electromagnetic sensors 26 may be communicatively sensors 26 , such as an array, may be used to providemultiple
coupled to computing system 30 and / or configured to output simultaneous measurements at multiple locations. For
detected signals to computing system 30 . In some embodi- example , electromagnetic sensors 26 may be disposed
ments , sensors 26 may be configured to detect and /or isolate 65 within a wellbore . Alternatively or in addition , an array of
the vertical component of the electromagnetic signals 22 . As electromagnetic sensors 26 may be disposed in the area
noted above, electromagnetic signals 22 may be emitted above and/or surrounding the wellbore to facilitate drilling
 US 9, 759,838 B2
11 12
operations and/or exploration of drilled fields. A more formation over the time period in which the signals are
detailed discussion of an example operation of such embodi detected . System 10 may thus be used to monitor the
ments is discussed below with respect to FIG . 7. More development and / or depletion of a hydrocarbon field and /or
detailed examples of sensors 26 are illustrated in FIGS. 2A , water well or aquifer over periods of production .
2B , and 2C . 5 Computing system 30 represents any suitable combina
Seismic sensors 28 represent any suitable combination of tion of hardware , software , signal processors, and control
sensing elements capable of detecting and/ or measuring at ling logic to process, store , and/ or analyze electromagnetic
least some portion of seismic signals 20 . For example , signals 22 and /or seismic signals 20 received from sensors
sensors 26 may be configured to detect the vertical compo - 26 and /or 28 . Computing system 30 may include one or
nent of seismic signals 20 . Seismic sensors 28 may be 10 more processors , memory , and /or interfaces. Computing
communicatively coupled to computing system 30 and/ or system 30 may , for example , include an interface operable to
configured to output detected signals to computing system communicatively couple with and / or receive information
30 . Seismic sensors 28 may include, but are not limited to , from sensors 26 and /or 28 . Computing system may be
geophones, hydrophones, and /or accelerometers , including operable to receive and /or process passive survey data from
digital accelerometers . Sensors 28 may represent a single - 15 sensors 26 and 28 . Passive survey data may include , for
component geophone , a two- component geophone , or a example, data representative of signals 20 and /or 22 . Com
three -component geophone. Sensors 28 may also represent puting system 30 may include one or more appropriate
a single -axis accelerometer, a two - axis accelerometer, or a analog -to -digital converters to digitize signals 20 and/ or 22
three -axis accelerometer. In some embodiments , seismic for digital signal processing . Alternatively or in addition ,
sensors 28 may represent one or more three -component 20 sensors 26 and/ or 28 may include appropriate analog -to
accelerometers . Additionally or alternatively , sensors 28 digital converters. Computing system 30 may include a
may represent any appropriate combinations of these types recording and /or storage device operable to receive and store
of seismic sensors . For example , multiple types of sensors data received from sensors 26 and 28 . Computing system 30
28 may be utilized by system 10 to detect seismic signals 20 . may include , for example , digital and/ or analog recording
Seismic sensors 28 may measure a seismic wave in multiple 25 devices and /or non - transitory media . In some embodiments ,
directions , for example in one or two directions parallel to computing system 30 may be capable of processing detected
the surface of the earth , in a direction perpendicular to the seismic signal 20 and the detected electromagnetic signal 22
surface of the earth , and/or in a vertical direction . in real -time without first recording the signals on a non
Seismic sensors 28 may be arranged in an array and /or in t ransitory medium .
a variety of patterns . For example, seismic sensors 26 may 30 Computing system 30 may form all or a portion of a
be arranged and/ or located in similar manners and locations recording vehicle, a housing structure, or a weather resistant
as discussed above with respect to sensors 26 . Any appro - enclosure located proximate sensors 26 and / or 28 . In some
priate number of seismic sensors 28 may be arranged in the embodiments , computing system 30 may be at least partially
array or pattern . For example , seismic sensors 28 may be enclosed in a weather -resistant enclosure . Accordingly, com
arranged in a similar manner as discussed above with respect 35 puting system 30 may be capable of recording passive
to electromagnetic sensors 26 . As another example , a grid survey data over days to weeks withouthuman intervention .
pattern may be used . Seismic sensors 28 may be laterally As shown below with respect to FIGS. 4 -6 , a computing
spaced apart by less than about one half of the wavelength system 30 may be enclosed in a dedicated recording vehicle .
of the highest frequency surface seismic waves expected to Moreover, while illustrated as external to sensors 26 and / or
be detected . That may include higher frequencies than those 40 28 , computing system 30 may be internal or external to a
expected to be produced by the electroseismic effect within housing of one or more sensors 26 and /or 28 . Moreover,
the subsurface earth formation . Seismic sensors 28 may be computing device 30 may be one of a plurality of computing
configured to attenuate and / or reject surface and / or horizon - devices 30 used to record one or more electric and /or seismic
tal seismic signals. Such signals may be caused by various signals . Computing device 30 may be capable of commu
sources including heavy equipment, vehicular traffic , and/ or 45 nicating with other computing devices 30 or other data
natural sources such as earthquakes and/ or thunder. processing servers over a network (not illustrated ). The
In some embodiments, a pattern and /or array of electro - network may be a wired or wireless communications net
magnetic sensors 26 may overlap with a pattern or array of work . Thus , any of the data processing techniques described
seismic sensors 28 . Signals detected by sensors 26 and /or 28 herein may be performed by one or more computing devices
may be transmitted to computing system 30 . In some 50 30 and/ or may be performed by a remote data processing
embodiments, the signals may be suitably recorded , for server, which may be capable of processing and correlating
example , using a conventional seismic field recorder. Addi- data from various computing devices 30 . An example
tionally or alternatively , each sensor may have its own embodiment of computing system 30 is discussed in more
recording device , and each recording device may be internal detail below with respect to FIG . 9 .
or external to the seismic sensor. It should be noted that 55 As illustrated in FIG . 1B , passive seismic source 40
while illustrated as including sensors 26 and 28 , system 10 represents any appropriate passive source of seismic energy .
may include only sensors 26 or only sensors 28 as appro - For example , passive source 40 may represent the earth ' s
priate for particular embodiments . Accordingly, any appro - natural seismic energy . Passive source 40 propagates seismic
priate combination of sensors 26 and / or sensors 28 may be energy into the subsurface of the earth as seismic signal 42 .
utilized . 60 Seismic signal 42 may represent , for example , a seismic
Sensors 26 and /or 28 may form all or a portion of a plane wave 42 . As seismic signal 42 propagates into the
long-term installation , which may be utilized for long- term earth , it may encounter various subsurface earth formations
passive surveying . Signals 20 and/or 22 may be detected at 16 . The interaction of seismic signal 42 and subsurface earth
multiple times over a period of time, which may be periods formation 16 may cause a seismoelectric conversion to take
of days , weeks , months, or years . Long -term surveys may 65 place at an edge and /or boundary 18 of subsurface formation
provide a time- based indication of various properties of 16 . As a result , one or more electromagnetic signals 22
subsurface earth formation 16 , including any changes in the and /or seismic signals 20 may propagate towards the surface
 US 9, 759,838 B2
13 14
of the earth . Electromagnetic signal 22 may be generated as FIGS. 1A and 1B are depicted in different figures for the
a result of a seismoelectric conversion as seismic signals 20 sake of clarity only . Accordingly , particular embodiments of
propagate towards the surface . Electromagnetic sensors 26 system 10 may be capable of utilizing signals 20 and/ or 22
may detect electromagnetic signals 22 . Seismic sensors 28 prorogated by passive electromagnetic source 12 and/or
may detect seismic signals 20. In some embodiments , seis - 5 passive seismic source 40 . Moreover , system 10 may be
mic sensors 28 may detect seismic signals 40 , which may be configured to utilize signals 20 and/or 22 from passive
used as a reference to detect a modulation of signals 20 electromagnetic source 12 at particular times while utilizing
and/ or 22 by subsurface earth formation 16 . signals 20 and /or 22 from passive seismic source 40 at
Passive seismic source 40 may represent earth ' s naturally particular other times and /or may utilize the signals at the
occurring seismic energy . Earth ' s naturally occurring seis - 10 same time. For example , passive electroseismic / seismoelec
mic energy may include a broad spectrum of frequencies, tric surveying utilizing passive seismic sources 40 and/ or
from sub -hertz frequencies to tens of thousands of hertz passive electromagnetic sources 12 may be collected during
frequencies, having a broad coverage over the surface of the drilling or fracturing or enhanced oil recovery to acquire
earth . This broad spectrum allows for a broad range of information about hydrocarbons and / or other fluids . Survey
penetration depths of seismic signal 42 from tens ofmeters 15 data from passive electromagnetic sources 12 may be col
to tens of kilometers. The corresponding frequencies of lected , for instance, when passive seismic sources 40 are
seismic signal 42 in the earth may result from variations in attenuated. For example, the drilling operation may be
passive source 40 due to various natural events such as Earth paused and / or finished . As another example , computing
quakes, tides , tectonic events, volcano activity , thunder, and system 30 may perform passive surveying during drilling ,
atmospheric pressure fluctuations. In some embodiments , 20 fracturing, and / or enhanced oil recovery to acquire infor
passive source 40 of seismic signals 42 may include cultural mation about hydrocarbons and /or other fluids .
sources of seismic waves , which may have sufficiently low In operation , system 10 detects, stores, and /or analyzes
frequencies to reach and interact with subterranean forma electromagnetic signals 22 and /or seismic signals 20 . Sen
tion 16 . As another example , passive source 40 may include sors 26 and 28 respectively may detect electromagnetic
well- drilling activities, pumping fluids , automobile noise , 25 signals 22 and seismic signals 20 . Each sensor may transmit
compressor noise , farming noise , and manufacturing noise , the detected signals to computing device 30 for storage
which may generate seismic signals 42 of appropriate and/ or processing. Computing device 30 may record the
strength and / or frequency to interact with subterranean resulting electromagnetic signals 22 and /or seismic signals
formation 16 . 20 . Computing device 30 may process electromagnetic
FIG . 1B includes several examples of passive seismic 30 signals 22 and / or seismic signals 20 to identify various
source 40, including passive seismic sources 40a - 40e. Pas - properties associated with subsurface formation 16 . Sensors
sive seismic source 40a may represent a source of seismic 26 and /or 28 may additionally or alternatively detect signals
energy resulting from a drilling operation . Passive seismic generated by subsurface earth formation 16 in response to a
source 40a may represent a localized drilling event at a electromagnetic signal 42 propagated from passive seismic
particular depth ( such as, for example , the head of a drill bit 35 source 40 . Computing system 30 may then process detected
or drilling apparatus interacting with the subsurface ) and/ or signals using various signal processing techniques to iden
may represent vibrations from drilling activities along a tify properties and/or features of subsurface earth formation
length of the hole and / or casing . Passive seismic source 40b 16 . Thus, the techniques discussed in the present disclosure
may represent a source of seismic energy resulting from may be utilized to analyze signals 20 and /or 22 generated as
horizontal drilling activities such as fracturing, hydrofrac - 40 a result of passive electromagnetic source 12 and /or passive
turing, or other drilling operations. Additionally or alterna - seismic source 40 . Certain examples of the operation of
tively, passive seismic source 40b may represent seismic system 10 provided below may be discussed with respect to
energy caused by fluid is moving through rock pore spaces a passive electromagnetic source 12 , but it should be noted
(which may be the result of hydrofracturing). Passive seis that the teachings of the present disclosure apply similarly
mic sources 40c and 40d may represent sources of seismic 45 and /or the same to signals generated by passive seismic
energy resulting from the Earth ’s natural seismic activity source 40.
and / or a microseismic or other natural event, as described System 10 may process the signals to determine the
above . Passive seismic source 40b may represent a source of existence of a fluid in subterranean formation 16 and / or
seismic energy resulting from a near- surface or surface other properties of the subterranean formation , such as the
event. Accordingly, passive seismic source 40 may include 50 existence of subsurface earth formation 16 and /or an indi
any appropriate source of seismic energy and /or may be cation that it contains a fluid , a depth of subsurface earth
located in any appropriate relationship to subsurface earth formation 16 , a porosity of subsurface earth formation 16 , a
formation 16 , including above, below , beside , or in subsur- fluid permeability of subsurface earth formation 16 , a com
face earth formation 16 . Additionally or alternatively pas - position and /or type of at least one fluid within subsurface
sive seismic source 40 may include seismic energy caused 55 earth formation 16 , a spatial extent of the subsurface earth
by a drill bit, fracturing rock , fluid moving through rock pore formation 16 , an orientation of the boundaries of the sub
spaces , wells where drilling or pumping activity occurs, surface earth formation 16 , a resistivity of subsurface earth
and / or by pollutant fluids migrating through the subsurface . formation 16 , or any combination thereof. Fluids detectable
Seismic signal 42 represents a seismic wave, seismic and/or identifiable by system 10 may include an aqueous
plane wave , or other appropriate seismic signal that propa - 60 fluid ( such as water ), a hydrocarbon , petroleum , carbon
gates into the Earth from passive source 40. Accordingly , dioxide , carbon monoxide, acid gases , helium , nitrogen ,
seismic signal 42 may emanate from any appropriate passive other subsurface minerals . System 10 may also be capable of
seismic source 40 , including those originating at the Earth ' s identifying and / or tracking migration of fluids, pollutants ,
surface and/ or located at some appropriate depth below the magma, and other subsurface fluids .
surface . For example , seismic signals 42a - 42e may respec - 65 System 10 may be moved during a measurement to detect
tively originate from passive seismic sources 40a -40e . It signals 20 and / or 22 at multiple locations . Thus, system 10
should be understood that the various signals illustrated in may be capable of generating and analyzing passive survey
 US 9, 759,838 B2
15 16
data across large survey areas . Moving system 10 may signal that can propagate into the earth , where the resulting
provide useful information for a screening or first look at an amplitude at the one or more electromagnetic sensors 26
area of interest. In some embodiments, the system 10 may be may be hundreds or thousands of times larger than the
disposed in a moving vehicle. For example , sensors 26 may desired background electromagnetic field within the earth .
be installed in a pattern into a movable device to facilitate 5 Similarly , unbalanced power -lines can generate 180 Hz
movement of the array . For example , sensors 26 may be noise and motors can generate 400 Hz noise . As a further
disposed in a trailer, rack , or cargo carrier connectable to a example , cathodic protection circuits can produce poorly
moving vehicle such as a truck or van . Sensors 26 may rectified alternating current ( AC ) signals at several frequen
alternatively be installed in a land vehicle , water vessel, or c ies that result in electromagnetic noise at the one or more
aircraft . System 10 may record and / or store signals 20 and /or 10 electromagnetic sensors 26 .
22 detected by sensors 26 and/or 28 , as described in more Computing system 30 may apply various noise reduction
detail herein . In some embodiment, system 10 may continu techniques , including a technique that may utilize a gener
ously and /or repeatedly detect signals 20 and /or 22 while ated reference signal that is demodulated to identify and /or
moving isolate electromagnetic signals 22 . The noise reduction
Computing system 30 may record signals 20 and /or 22 15 schememay be used to generate a signal that may have an
over various periods of time as appropriate . Computing increased signal-to - noise ratio relative to the full spectrum
system 30 may utilize sampling techniques to ensure an of the electromagnetic field 14 . For example , a reference
adequate representation of the detected signals. A minimum signal may be generated by a reference signal generator and
sampling rate may be determined based on the frequency of introduced into the near surface 24 of the Earth . The
the sampled signals. In general, the sampling rate for the 20 reference signal generatormay transmit the reference signal
analog -to - digital conversion should be at least twice the into the earth from a location near to the ground . Electro
highest frequency of interest in order to properly represent magnetic signals 22 may modulate the reference signal in
the recorded waveform . However, higher order sampling the same way as the vertical portion of electromagnetic
may be utilized , including various oversampling techniques. signals 22 . Upon detecting the modulated reference signal
Longer recording times may allow for better signal to noise 25 with sensor 26 , computing system 30 may then compare the
ratios (SNRs) and may accordingly increase reliability of the detected signal with the known reference signal and isolate
detected signals. electromagnetic signals 22 for further processing . The
Computing system 30 may process detected signals 20 detected , modulated reference signal may , in some embodi
and/ or 22 to determine particular properties of the subsur - ments , be filtered or otherwise pre -processed prior to being
face earth formation , including any one or more of the 30 compared and isolating electromagnetic signal 22. For
properties discussed above. Computing system 30 may example , a lock - in amplifier may be used to isolate electro
process the signals at substantially the same time as the time magnetic signal 22 from the detected signal. The reference
the signals are detected and/or may store the signals to signal generator may be coupled to the lock - in amplifier 804
process the signals at a later time. Computing system 30 may or may form a part of the lock - in amplifier. The reference
be configured to apply various digital signal processing 35 signal and the detected modulating signal may be input to
techniques to the detected signals . For example , computing the lock -in amplifier. The lock - in amplifier may produce a
system 30 may apply a series of pre - processing steps to the signal comprising electromagnetic signal 22 with an
detected signals , including applying various filtering tech - improved signal-to - noise ratio as compared to the signal
niques calculated to remove noise and / or isolate signals of detected by the sensor 26 . The existence of a modulation of
interest from the detected signals . After pre -processing , 40 the reference signal may be taken as an indication that a
computing system 30 may determine from the processed coupling has occurred due to the interaction of the reference
data various properties of subsurface earth formation 16 . signal with electromagnetic signals 22 . Electromagnetic
Computing system 30 may, for example , correlate the pro signals 22 may then be isolated based on the fact that
cessed data to identify properties of subsurface earth for electromagnetic signals 22 may have narrower frequency
mation 16 . Each of these steps are discussed in greater detail 45 band spectrum than the reference signal and /or may have
below . recognizable and extractable characteristics . The produced
Pre - Processing of Detected Signals 20 and /or 22 signal may then be sent to one or more additional, optional
Computing system 30 may apply various pre -processing pre -processing steps before being passed on for further
techniques to data received from sensors 26 and /or 28 in analysis .
order to identify and/or isolate signals 20 and/or 22 from 50 Depending on the type of sensors 26 and/ or 28 used to
other sources of electromagnetic signals that may be detect the signal, electromagnetic signals 22 and /or seismic
received by sensors 26 and/ or 28 . For example , to isolate signals 20 may include an alternating current (AC ) portion
electromagnetic signals 22 , computing system 30 may apply and direct current (DC ) portion . The DC portion of the signal
a noise reduction scheme utilizing a generated reference may result from the detection of one or more portions of the
signal that is detected and /or demodulated to identify and/or 55 earth 's electromagnetic field 14 and may not be represen
isolate electromagnetic signals 20 . Computing system 30 t ative of electromagnetic signals 22 or seismic signals 20 .
may also apply other noise reduction techniques, such as Accordingly , the DC portion may represent noise that may
isolation of direct current components of the signal, digital be filtered out prior to analysis of signals 20 and/ or 22 . The
sampling techniques , and analog and /or digital band -pass DC portion may be filtered and/or removed using any
filtering 60 appropriate techniques , such as using a capacitive filter or
Coherent noise refers to cyclic signals 20 and /or 22 that other elements of the sensor 26 and/ or 28 design and /or
have an approximately constant frequency over a predeter - using a digital filter implemented in software.
mined measurement period . Many coherent, electromag Digital sampling techniques including data decimation
netic noise sources can be found in a typical measurement may be utilized to limit and / or filter the data to be processed .
setting and can be accounted for through various processing 65 Decimating may refer to any appropriate technique for
techniques. For example, the power - line frequency of 60 reducing the effective sampling rate . To the extent appro
Hertz (Hz) can generate a high amplitude electromagnetic priate , decimation may reduce the amount of data that is
 US 9 ,759,838 B2
17 18
processed in the analysis steps, which may reduce process - Horizontal components of electromagnetic signals 22
ing times . The signal data may typically be decimated down and /or seismic signals 20 may be rejected in any appropriate
to an effective sampling rate approximating two times the manner. For example , multiple electromagnetic sensors 26
highest frequency of interest while allowing for an identi may be disposed in an array and may be used to detect one
fication of the frequency characteristics in the data. Higher 5 or more horizontal and /or vertical components of the elec
decimation rates may be used , for example , when a faster, tromagnetic signal 22 . Similarly , horizontal seismic noise
and possibly less accurate first look at the data is desired . In may also be rejected in detected seismic signals 20 . In
some embodiments, the signals 20 and/or 22 may be over particular, detected seismic signals 20 may be filtered in the
sampled and / or averaged over one or more frequencies spatial domain to reject surface waves traveling horizontally
and/ or frequency ranges to reduce the effects of momentary 10 across
fluctuations in the electromagnetic field 14 and/ or signals 20 may beseismic sensors 28 . One or more seismic sensors 28
configured to measure a horizontal component of
and /or 22 . For example, signal amplitude may be selected to seismic signals 22 , which may be used to generate the
be averaged by computing system 30 at one or more fixed
horizontal components used in the spatial filter. Accordingly ,
frequencies present in the detected seismic signal 20 and /or
electromagnetic signal 22 . It should also be noted that 15 a horizontal component of electromagnetic signal 22 and /or
seismic signals 20 may require certain characteristic propa seismic signal 20 may be used as a predictive filter to
gation times for a seismic wave that originates at subterra remove noise from the vertical component of the electro
nean earth formation 16 to reach the Earth 's surface. The magnetic signal 22 and /or seismic signal 20 . The predictive
averaging process may include identifying the characteristic filter may utilize horizontal components detected by one or
times of seismic propagation from the subterranean forma- 20 more electromagnetic sensors 26 and / or sensors 28 .
tion . The averaging process may include measuring and /or Spatial filters may also be applied to reject local seismic
sampling the signal amplitude for a length of time, which noise that may be detected by seismic sensors 28 . In some
may be more than twice the period of oscillation , and embodiments , local noise waves may propagate across the
averaging the signal amplitude over the detection time plurality of seismic sensors 28 in expected spreading pat
period. 25 terns , which may be analogous to water waves on a pond .
Various filtering techniques may be utilized to isolate The propagating noise waves may be suppressed by deter
signals 20 and/ or 22 , reduce noise , and/ or increase SNR . For mining the direction of travel and speed , and applying a
example , signals 20 and / or 22 may be filtered with a spatial filter thatmakes use of the spreading symmetry of the
band -pass filter to isolate one or more frequency bands of noise wave . The spatial filter may remove the local noise
interest. Noise may be filtered using a high pass filter, a low 30 from seismic signals 20 detected by each sensor 28 . In some
pass filter, wide band frequency filter, and /or narrow band embodiments, a predictive filter may be employed to predict
frequency filter, or other appropriate noise filter. In some the arrival and amplitude of the localnoise wave at a seismic
embodiments , ambient and /or naturally occurring sources of sensor and remove the local noise wave during the genera
electromagnetic radiation , such as electromagnetic signals tion of the detected seismic signal 20 . As noted above, one
14 and / or passive electromagnetic source 12, may be used to 35 or more of seismic sensors 28 may be configured to measure
determine the frequency range , amplitude range , and /or a horizontal component of the seismic wave . These seismic
other parameters of a desired noise filter. sensors 28 may also be used to determine the spreading
Coherent noise sources may not have exactly constant geometry of the local noise wave . The spatial filter may then
frequency over a predetermined measurement period. These be applied to each of the plurality of seismic sensors 28 ,
imperfections may be due to phase changes in the coherent 40 including those that may not be configured to measure a
noise sources . For example , electromagnetic noise generated horizontal component of the seismic wave . In some embodi
by power lines can experience some variations in the power - ments , one or more additional seismic sensors 28 used for
line voltage . Computing system 30 may monitor the phase local noise rejection may be deployed at a distance away
of the coherent noise source to adjust the start times to from the seismic sensors 28 measuring seismic signals 20 .
correspond to the phase of the coherent noise for each 45 The ability to measure the local noise wave at a distance
interval. The coherent noise source may also experience from other seismic sensors 28 may provide better prediction
amplitude variations over time, which may result in a partial of the local noise wave and an improvement of the reduction
cancellation of the coherent noise upon the summing of the of the local noise wave in the detected seismic signal .
intervals . In an embodiment, computing system 30 may To enhance spatial continuity across seismic sensors 28 .
apply a frequency filter, such as a frequency notch filter , to 50 seismic signals 20 detected by multiple seismic sensors 28
the detected electromagnetic signals 22 to further enhance may be cross - correlated and /or summed . Summed seismic
the signal-to -noise ratio and/ or reduce a portion of the signals 20 may be used as a predictive filter to enhance
coherent noise in the background electromagnetic field . spatial continuity . Summed seismic signals 20 may result in
The techniques used to remove at least a portion of an increase in the amplitude of the seismic waves arriving at
coherent noise from the detected electromagnetic signals 22 55 the same time, for example , from a plane wave . Summed
may also be applied to the detected seismic signals 20 . seismic signals 20 may tend to cancel sources of local noise
Various sources of coherent seismic noise may be present in and /or components of seismic signals 20 that are not trav
a typicalmeasurement setting, including for example , motor eling as a plane wave . In some embodiments , a dip filter may
noise and industrial equipment. It should be noted that the be utilized to reject noise . For example , the fact that the
start time and duration for each corresponding interval of 60 seismic signals 20 resulting from one or more electroseismic
both the detected electromagnetic signals 22 and the conversions may be a plane wave may be used to remove at
detected seismic signals 20 may be the same to improve least a portion of a noise signal from the detected seismic
cross -correlation of the signals . In some embodiments, the signal 20 . In particular, a dip filter can be used to reject
start time and duration may be chosen to allow cancellation detected seismic signals 20 arriving at a non -normal angle to
ofat least a portion of the coherent noise in both the detected 65 the seismic sensors 28 . In some embodiments , the dip filter
electromagnetic signals 22 and the detected seismic signals may be applied after cross - correlating the detected seismic
20 . signals from two or more of the seismic sensors .
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19 20
Processing Signals 20 and /or 22 properties, such as ratios of power spectral densities, FFT
After any of the above optional pre-processing steps are amplitudes, and/or phases. A particular detected signal 20
performed , the resulting filtered signals 20 and /or 22 may be and/ or 22 that includes various white noise portions may be
processed to determine one or more properties of subsurface used as a base set of spectral properties thatmay be used as
earth formation 16 . Processing may include extracting an 5 a basis for comparison . For example, the base spectral
envelope of the filtered signals 20 and/or 22 , applying properties may be used to normalize other calculated ratios .
various frequency -domain processing and /or analysis steps , It should be noted , however, that other mathematical trans
and other processing techniques as explained in more detail formations may be used to produce similar results .
below . The existence of hydrocarbons in a formation may be Computing system 30 may analyze and correlate the
indicated by the existence of a modulation in signals 20 10 ratios of spectral properties as a function of the band -pass
and/ or 22 . In terms of the signal analysis described in this frequencies of the original signals 20 and /or 22 and/ or as a
section , the modulation may be identified by computing function of the frequency band of the extracted envelopes .
system 30 by demodulating a portion of the detected signals Based on the analysis , computing system 30 may determine
20 and/ or 22 to determine if an envelope can be identified . information about the frequency characteristics of themodu
If no envelope is found that is distinguishable from white 15 lating signal and / or an amplitude correlation relating the
noise , for example, or some other suitable reference signal, strength of the modulating signal for each frequency. Varia
then this result may be taken as evidence that there are no tions within the analysis may be used as feedback to adjust
hydrocarbons in subsurface formation 16 . If a suitable the analysis criteria such as increasing the bandwidth of the
envelope is identified , then the analysis described herein band -pass filters , which may be expected to increase the
may be carried out to identify the spectral properties of the 20 amplitude of the ratio of the power spectral properties. The
envelope and correlate the results with the presence of properties of the analysis may be tailored based on the
various fluids as well as a time and/ or frequency -depth quality and amount of data obtained , the type of signals
function. In some embodiments, other surveys as described present and interacting with a formation of interest, and a
below may be performed when an envelope is identified desired processing speed and cost.
Pre -processed signals 20 and /or 22 may pass to a signal 25 Computing system 30 may process the obtained power
envelope extraction step in which computing system 30 spectral density by de -trending the power spectral density
determines an envelope of the signal in the band of interest and/or integrating the power spectral density. Computing
The envelope of the signal may refer to the shape of the system 30 may then perform a correlation analysis of the
modulation of the signal. The modulation , and therefore the detected electromagnetic field in the time domain , the fre
envelope, can comprise one or more of a frequency modu - 30 quency domain , or both . For example , after de -trending and
lation , a phase modulation , or an amplitude modulation . An integration , computing system 30 may determine a FT of the
envelope detector used to extract the envelope of the signal power spectral density. The FT of the power spectral density
may be implemented in hardware or software . The envelope may yield correlations between the source electromagnetic
detector may demodulate signals 20 and/or 22 to determine field 14 and secondary electromagnetic fields 22 generated
and / or extract the signal envelope. Various demodulation 35 by seismic signals 20 by the seismoelectric effect in near
techniques may be used to extract the signal envelop , surface formation 24 . The properties of the analysis may be
including the Hilbert transform method. tailored based on the quality and amount of data obtained ,
If a signal envelope has been obtained , computing system the type of signals present and interacting with a formation
30 may analyze the envelope to calculate one or more of interest, and a desired processing speed and cost. In such
spectral properties . Spectral properties may include ampli- 40 embodiments , computing system 30 may determine the
tude and frequency characteristics of a signal and / or enve - existence of hydrocarbons in subsurface earth formation 16
lope , as well as other characteristics of the signal and/ or may be indicated based on the existence of strong correla
envelope , such as phase characteristics . Determination of tions between the source electromagnetic signal 14 and the
spectral properties may allow computing system 30 to secondary electromagnetic signals 22 generated by seismic
compare the envelope with one or more additional envelopes 45 signals 20 through the seismoelectric effect in near- surface
for additional signal bands. Spectral properties may be formation 24 . Seismic signals 20 may be generated by
determined in the frequency domain by calculating the electroseismic effects at subsurface earth formation 16 at
Fourier Transform and /or power spectral density . For correlation times that may correspond to known seismic
example , the power spectral density for various bands of transit times between hydrocarbon formations and the sur
frequencies may be calculated to give the power carried by 50 face of the earth . Seismic transit times can be obtained
the envelope expressed in units of power per frequency . explicitly from seismic data obtained in the area of interest
Alternatively or in addition to the power spectral density, a or can be estimated based on rock acoustic properties .
Fourier Transform (FT) , such as a Fast Fourier Transform Correlation of the spectral properties of the envelope and
(FFT) and/or complex FFT, may provide an indication of the presence of various fluids in subterranean pore spaces
various frequency characteristics of the envelope, including 55 may be based on a variety of classification methodologies.
the frequency distribution . Furthermore , the power spectral For example , statistical regression analysis , and statistical
density and FT calculationsmay provide relative amplitudes classifiers such as neural networks , decision trees , Bayes
of each of the frequencies identified . Calculation of the based classifiers, fuzzy logic -based classifiers, and conven
spectral properties may be implemented in hardware and/ or tional statistical classifiers may all be used to determine a
software . In some embodiments , computing system 30 may 60 time-depth and/ or frequency -depth relationship . For
determine one or more of spectral properties using a lock -in example , the analysis may be performed with the system and
amplifier and/or a spectrum analyzer. methods described herein at locations with known properties
Once spectral properties have been calculated , computing and formation characteristics to train and/or determine the
system 30 may compare corresponding values in certain correlation parameters . Once the parameters have been
frequency bands to the corresponding spectral properties in 65 determined , such as through adequate training to a neural
other frequency bands . Based on the comparison , computing net, computing system 30 may repeat the analysis in a new
system 30 may generate one or more ratios of the spectral location.
 US 9, 759,838 B2
21 22
Additionally or alternatively , computing system 30 may sets. Cross -correlation may be carried out at a variety of
perform power spectral analysis and obtain relative power points in the analysis of each signal as described above with
ratios of the modulating signal 20 and/ or 22 relative to a respect to the processing of electromagnetic signals 22 and
background signal to determine the frequency characteris - seismic signals 20 , either together or individually .
tics of the modulating signal. The time and/ or frequency 5 In some embodiments , computing system 30 may cross
characteristics may be used to derive depth and location correlate the detected electromagnetic signals 22 with the
information about the source and strength of the modulating detected seismic signals 20 to isolate at least a portion of the
signal, thereby revealing information about the location detected seismic signal 22 . For example , electroseismic
and / or depth of a subsurface earth formation 16 . A variety of conversion may generate a seismic response to a time
models may be used to correlate the spectral analysis results 10 dependent electromagnetic field with a corresponding time
with the depth of the modulating signal. For example , depth dependence . Accordingly, the resulting seismic signals 20
of the subsurface formation 16 may be determined based on may have the same time- dependence as the electromagnetic
a time depth function and /or frequency depth function . signals 14 , delayed by the seismic travel time. Electromag
While a correlation generally exists between the frequency netic signal travel time may be neglected because the
of modulating signals 20 and/ or 22 and the depth at which 15 electromagnetic propagation time down to the reservoir may
those signals originate , the exact correlation may or may not be much shorter than the seismic travel time to the surface .
be evident from the analysis of the signal detected by sensors This result may be used to remove at least a portion of a
26 and/ or 28 . Accordingly , a time- depth and /or frequency - noise signal that does not possess the expected time depen
depth function may be established using known or prede - dence between the detected electromagnetic signals 22 and
termined locations, parameters , and /or calculations. The 20 the detected seismic signals 20 .
depth values for similar locations may be determined based One or more harmonic signals may be detected and/or
on those predetermined characteristics once the spectral isolated in the detected seismic signal using a variety of
characteristics of the signals are analyzed and determined methods. In some embodiments , the detected seismic signal
The time- depth and/ or frequency -depth relationship for sig - may be cross - correlated with the detected electromagnetic
nals 20 and/ or 22 may depend on the Earth ' s resistivity , 25 field . A frequency analysis of the data resulting from the
formation properties , types of components present, and/ or cross -correlation may be used to identify frequencies in the
various electrical properties of a particular geologic area . detected seismic signal that are higher than those present in
Accordingly, new and/ or modified time- depth and /or fre - the detected electromagnetic field . The frequencies present
quency - depth functions may be determined and /or applied in the detected electromagnetic signal 22 may then be used
as computing system 30 is moved from location to location . 30 to remove at least a portion of the corresponding frequen
In some embodiments, a time-depth and/or frequency - depth cies , including fundamental frequencies, from the detected
function for one area may provide an adequate estimate for seismic signal 20 using , for example , filtering techniques as
another area depending on the relative characteristics of is discussed above . The frequencies may also be utilized by
those areas. Time-depth and /or frequency - depth functions computing system 30 to detect and/or isolate one or more of
may be derived from pre -existing empirical data obtained 35 the harmonic signals , which may include coherent harmonic
from previous geophysical surveys and / or exploration . signals .
Other suitable sources of data to determine a frequency - Computing system 30 may , in some embodiments, detect
depth function may be considered , such as conventional skin and/or isolate the harmonic signals by partially rectifying the
effect conductivity analyses . Based on a time- depth and/ or detected seismic signal 20 and/ or the harmonic signals
frequency -depth function and particular signals 20 and/or 40 detected and /or isolated from the detected seismic signal 20 .
22 , computing system 30 may derive depth information The harmonic signals may resemble a partially - rectified sine
associated with subsurface earth formation 16 . wave , which may be asymmetrical about zero amplitude . In
Techniques for Identifying Particular Properties some embodiments , the positive amplitudes may be larger
Computing system 30 may utilize various correlation than the negative amplitudes. The resulting asymmetry may
techniques, which may be used to identify particular prop - 45 be utilized by arbitrarily reducing the positive portions of the
erties of subsurface formation 16 . In some embodiments , source waveform before cross -correlation . In some embodi
passive surveying may be carried out by sequentially detect- ments, the negative amplitudes may be larger than the
ing and / or separately processing electromagnetic signals 22 positive amplitudes. The resulting asymmetry may be uti
and seismic signals 20 . For example, the detection of both lized by arbitrarily reducing the negative portions of the
electromagnetic signals 22 and seismic signals 20 may occur 50 source waveform before cross - correlation . Signal measure
at different times and /or locations . In some embodiments, ment and processing may be used to determine which
detection may occur during overlapping time periods and /or portion of the amplitude , such as the positive amplitude
at the same locations. The two types of signals may be portion or the negative amplitude portion , if either, is larger.
cross-correlated to determine various properties of the sub Any of the aforementioned pre- processing techniques may
surface earth formation 16 . 55 be applied before computing system 30 cross - correlates the
Cross -correlation , which may also be referred to as joint detected harmonic signals in the detected seismic signal 20
processing, may be used to identify features in common to with the detected electromagnetic signals 22 and/ or one or
data from both signals . For example , electroseismic and more harmonic signals in the detected electromagnetic sig
seismoelectric signals may originate in the same physical nals 22 . An autocorrelation of the detected electromagnetic
conversion mechanism at boundaries 18 between dissimilar 60 signals 22 may have lower frequency components than the
rocks or at boundaries 18 between different fluids in rock autocorrelation of the detected seismic signals 20 . In some
pore spaces . Sensors 26 and 28 , however, may not be equally embodiments , the detected seismic signal 20 may be band
sensitive to rapid signal changes or to small signal amplitude pass filtered to remove frequencies below the fundamental
differences . Thus, the processed electromagnetic signals 22 frequencies present in the detected electromagnetic signals
and seismic signals 20 may be similar but may not be 65 22 , which may be used to identify the harmonic signals . The
identical. Cross -correlation by computing system 30 may filter may be applied before processing the detected seismic
enhance and /or isolate the common information in both data signal and the detected electromagnetic field . In some
 US 9 , 759,838 B2
23 24
embodiments , the detected harmonic signals may be pro netic field' s polarization . In one polarity of the background
cessed with the detected electromagnetic signals 22 to electromagnetic field 14 , the conversion surface looks like a
determine at least one property of the subsurface earth simple resistor. In the opposite polarity it appears to be a
formation 16 . In some embodiments , the processing of the capacitor with a long RC time constant. This time constant
detected harmonic signals with the detected electromagnetic 5 may at least partially smooth out one polarity of the source
signals 22 may comprise cross-correlating the detected signal, resulting in one polarity having an observable
harmonic signals with the detected electromagnetic signals induced polarization while the opposite polarity may not .
22 . The degree of induced polarization may act as an indicator
Computing system 30 may detect and/ or isolate one or
more nonlinear signals using any appropriate technique . The 10 the thepolarity
of resistivity of the interface, and the determination of
being affected may act as an indicator of the
nonlinear signals in the detected electromagnetic field ,
which may include harmonic signals, may result from the orientation of the rock interface.
conversion of the electromagnetic energy in the earth 's The properties of the background electromagnetic field 14
background electromagnetic field to seismic energy, as may be spatially dependent, allowing for a determination of
described in more detail above . This point of conversion 15 the lateral extent of the subsurface earth formation 16 . The
may also result in a frequency shift or time delay in the extent of the lateral variation in the induced polarization and
electromagnetic energy in the earth 's background electro - generation of nonlinear signals may be smoothed out due of
magnetic field , generating nonlinear signals . At least a the long wavelengths present in the earth 's background
portion of the resulting nonlinear signals may be detected by electromagnetic field 14 . As a result, the detected electro
the electromagnetic field detectors and used to determine at 20 magnetic field may have a limited resolution with respect to
least one property of the subsurface earth formation . the edges 18 of the reservoir .
In some embodiments, the interface 18 where electroseis - In some embodiments, low frequency measurements ,
mic conversions occur can bemodeled as a charged capaci such as frequency measurements below 1 Hz, earth ' s back
tor that comprises a planar region of high resistance and an ground electromagnetic field 14 may be useful in measuring
existing , internal electromagnetic field . The interface can 25 the polarity dependence of the induced polarization . In the
then be understood as having a resistor -capacitor (RC ) time measurements of the seismic signals 20 resulting from the
constant. The RC time constant may vary over a consider - electroseismic conversions, the seismic wavelengths may be
able range of values depending on the resistance of the rock useful for spatial delineation and the seismic velocity may
interface 18 and the internal electric field . The RC time be useful for depth determination . In these measurements ,
constant may have the effect of smoothing out a portion of 30 frequency and time information may be important charac
the background electromagnetic field 14 , which may be terizations . In some embodiments, the frequency and time
detected by one or more of the electromagnetic sensors 26 . information may be determined by integrating the ampli
In some embodiments , the extent of the resulting smoothing t udes of different polarities in the detected electromagnetic
of the background electromagnetic field 14 may be used field and the detected seismic signal from one or more
during processing to determine at least one property of the 35 seismic sensors .
subsurface earth formation . The background electromag - The nonlinear signals in the detected electromagnetic
netic field 14 may bemodified depending on the orientation signals 22 resulting from the conversions at the subsurface
of the background electromagnetic field 14 with respect to earth formation interfaces may be detected using a variety of
the interface 18 . When the background electromagnetic field methods. In some embodiments, the positive and negative
14 is parallel to the internal electric field at the interface 18 , 40 polarities of the earth ’s background electromagnetic field 14
the internal field and internal stresses may not be modified may have different amplitudes and different frequency spec
significantly . In this orientation , the interface 18 behaves as tra after being affected by the interface . These differences
a simple resistor of high value with mobile fluids in the pore may be used in determining the nonlinear components of the
space , and the RC time constantmay not significantly affect detected electromagnetic signals 22. The resulting linear
the background electromagnetic field 14 . However, some of 45 electroseismic response may be detected from the detected
the electrical field energy may be converted into seismic seismic signal at one or more seismic sensors. Through a
energy in the electroseismic response . cross- correlation , the resulting linear components of the
When the background electromagnetic field 14 is anti- detected electromagnetic signals 22 may be determined and
parallel with respect to the internal field at the interface 18 , isolated by computing system 30. Using the linear compo
the internal chemical reactions may be temporarily halted , 50 nents as a filter, the non - linear components may be isolated
the stresses and effective resistance may be reduced , and the from the detected electromagnetic field . The filtered elec
net electric field may decrease . In this orientation , the tromagnetic signals 22 may be further processed to identify
applied field may be at least partially rectified to a reduced the nonlinear components or reduce any noise signals pres
value and the change in internal stresses may produce a ent in the remaining detected electromagnetic field after
seismic response . In terms of the overall subsurface earth 55 being filtered . For example , additional filters may be applied
formation , the earth ' s background electromagnetic field may and /or autocorrelations performed
be at least partially rectified at the boundaries between rock In some embodiments , the detected electromagnetic sig
masses . As a result, the earth ' s background electromagnetic nals 22 may be compared to the earth ' s background elec
field 14 that is interacting with a charged dipole layer where tromagnetic field 14 measured at a distant location . The
an electroseismic conversion occurs may be altered , and the 60 detected electromagnetic field may have harmonic frequen
alterations may be detected by one or more sensors 26 cies and low frequencies that are not present in a signal
configured to detect background electromagnetic field 14 . In measured at a distant point. In this embodiment, detected
some embodiments , the partial rectification of the back - electromagnetic signals 22 at a distant electromagnetic sen
ground electromagnetic field 14 may be used to determine sor 26 may be used to filter the detected electromagnetic
an orientation , resistivity , or both of at least one interface 18 65 signals 22 above the subsurface earth formation 16 . The
in the subsurface earth formation 16 . The apparent subsur - remaining signal present after applying the filter may con
face resistivity may depend on the background electromag - tain the various harmonic , nonlinear, and/or low frequencies
 US 9 , 759,838 B2
25 26
of interest. These signals may be further processed or tions around a site of interest when a plurality of locations
filtered , for example to remove one or more noise signals . are used to measure the signal of interest. The resulting
In some embodiments , any harmonic , nonlinear , and /or hydrocarbon indications and resulting depth measurements
low frequencies present in the detected electromagnetic field may be used to generate a two dimensional, a three dimen
above the subsurface earth formation of interest may be 5 sional, and/ or a time-dependent model the subterranean
detected by comparing the detected electromagnetic field earth formation 16 and /or the one or more fluids contained
measured in the earth to those measured in the atmosphere . therein . In some embodiments, computing system 30 may be
If the earth 's background electromagnetic field 14 modula - capable of generating models using any appropriate combi
tion creates a seismic response , then the surface where nation of survey data obtained from any one or more of the
energy conversion occurs may behave as a source of elec - 10 survey techniques discussed below with respect to FIG . 3 .
tromagnetic radiation since there is a finite region ofmodu - Two dimensional, a three dimensional, and /or time-de
lated electromagnetic field and charge separation . The pendentmodel may include one or more images and /or maps
earth 's background electromagnetic field within the earth of subsurface earth formation 16 . For example , computing
may itself take on a character reflecting the nonlinear system 30 may utilize passive seismoelectric and /or elec
conversion . The resulting electromagnetic radiation may 15 troseismic data to develop a two - dimensional or three
manifest itself as a change in boundary conditions at the dimensionalmap of the subsurface and /or subsurface zones .
earth 's surface . Specifically, the resulting electromagnetic Various survey data from any of the techniques in the present
radiation may create a vertical electric field thatmay not be disclosure may be correlated to identify particular features
continuous across the earth /atmosphere boundary . The use of a particular portion of the image and/ or map . For
of a detected electromagnetic field above the surface of the 20 example , survey data that is particularly reliable at identi
earth may be used to filter the detected electromagnetic field fying particular features may be used as a baseline for
within the earth . The remaining signal present after applying comparison with other survey data . As another example ,
the filter may contain the various harmonic , nonlinear, survey data for a particular coordinate and/or location in the
and/ or low frequencies of interest. These signals may be model may be available from a first survey method but not
further processed or filtered , for example to remove one or 25 available from a second survey method. Alternatively or in
more noise signals . addition , computing system 30 may be capable of determin
Generating Models of Subsurface Earth Formation 16 ing the reliability and/ or accuracy of particular survey data
Various properties of the subterranean formation 16 may and may determine to utilize a first portion of geologic data
be utilized to develop a geologicalmodel of the subterranean from one methodology over a second portion of geologic
earth formation 16 . Various modeling programsmay be used 30 data from another methodology .Moreover, in some embodi
to develop the model of the subterranean formation and can ments , computing system 30 may be capable of, based on
provide predicted outputs based on themodel. The predicted reliability determinations , to utilize a particularly reliable
outputs can then be compared with the detected signals 20 data point from a first survey technique as an assumption
and/ or 22 to determine if the model is accurate . When a when processing and/or interpreting data from another sur
discrepancy is detected , the geological model can be altered 35 vey technique . For example , resistivity information deter
and the process repeated . Such a process may result in a mined from controlled - source electromagnetic (CSEM ) sur
match between the geologicalmodel and the detected signal, veying and /or depth information from active source
thereby providing one or more properties of the subterranean surveying may be utilized as assumptions when interpreting
formation 16 . Computing system 30 may be capable of passive source electroseismic and/ or seismoelectric survey
generating various models of the subsurface earth formation 40 data . Accordingly , information from various survey meth
16 , including three -dimensional models and time-depen - odologies may be interleaved, interpolated , extrapolated ,
dent, or four-dimensional, models. The four -dimensional and /or combined as appropriate to form the image and/or
models may be generated based on signals 20 and / or 22 map of subsurface earth formation 16 .
detected over time. Four-dimensional models may thus FIGS. 2A , 2B , and 2C are block diagrams illustrating
illustrate time-dependent properties of subsurface formation 45 example sensors 26 for passive electroseismic and seismo
16 , including amounts of fluids produced from the reservoir electric surveying . As illustrated in the FIG . 2A , sensor 260
16 , changes to the formation 16 over time, effects of may be a particular embodiment of sensor 26 that includes
hydrofracturing , migration of pollutants and /or magma, and one or more conductive elements 202 and 204 , coupling
other time- dependent properties . network 210 , amplifier 208 , and signal processing unit 209 .
Accordingly , the detection and analysis steps may be 50 Sensor 260 may be capable of detecting electroseismic
repeated by computing system 30 any number of times . For signals 22 , as previously discussed above with respect to
example , multiple measurements may be made at a single sensor 26 . Sensor 260 may output a signal representing
location over several time periods. The results may be detected electromagnetic signals 22 . Sensor 260 may be
statistically analyzed to provide an improved accuracy cor installed and/or disposed in any appropriate housing, includ
relation and/ or survey . In addition , one or more samples may 55 ing weather -resistant housing, movable vehicles , and /or
be taken at varying locations sequentially in time or con - permanent installations, as is discussed above with respect
currently in time using one ormultiple sensors 26 and /or 28 . to sensor 26 . Sensor 260 generally operates by comparing a
For example , multiple measurements may be made at vary stable reference voltage to a voltage measurement respon
ing locations around a site of interest. Various grid patterns sive to electromagnetic signals radiated from the ground .
and / or random sample locations may be chosen to generate 60 Accordingly , sensor 260 may be configured to sense varia
a plurality ofmeasurements across an area . For example , the tions in the ground signal , which may be wholly or partially
grid and /or array of detectors described above may be used comprised of electromagnetic signals 22, as compared to a
to generate a plurality of detected signals for use with the reference voltage .
processing techniques described herein . The multiple mea - Conductive elements 202 and 204 are generally capable
surements may be performed sequentially or concurrently at 65 of measuring electromagnetic signals radiated from the
a single location , and/ or the measurements may be per - ground . As illustrated conductive element 202 measures a
formed sequentially and/or concurrently in the various loca - stable reference voltage , while conductive element 204 is
 US 9, 759,838 B2
27 28
generally capable of measuring the vertical component of system 30 . For example , amplifier 208 may be capable of
electromagnetic signals 22 . Conductive elements 202 , 204 outputting detected electromagnetic signals 22 to computing
may represent any appropriate capacitive and /or conductive system 30 . Amplifier 208 may, in some embodiments,
plates or other sensing elements . As illustrated , conductive include appropriate analog -to -digital converters for digitiz
elements 202 and 204 are capacitive plates that are arranged 5 ing detected electromagnetic signals 22 .
parallel to the surface of the Earth . A generally parallel Signal processing unit 209 represents any appropriate
arrangement to the surface of the Earth may allow conduc combination of hardware, software , and other components
tive element 204 to respond to and /or measure the vertical operable to process the output of amplifier 208 . For
component of electromagnetic signals 22 , which may rep - example , signal processing unit 209 may be capable of
resent a vertical electric field . Similarly , conductive element 10 implementing any one or more of the pre -processing steps
202 may be shielded from and / or configured not to measure discussed above with respect to FIG . 1 . Signal processing
the vertical component of electromagnetic signals 22 . In unit 209 may be hardware - implemented portion of sensor
some embodiments , conductive elements 202 , 204 may form 260 and /or may form a portion of computing system 30 .
a capacitor. Conductive elements 202 , 204 may be a con - Signal processing unit 209 may include one or more notch
ductive metal such as copper, aluminum , or stainless steel. 15 filters , low pass filters , high pass filters , clamping circuits ,
Particular embodiments of conductive elements 202 , 204 sample and hold circuits , or any other appropriate signal
may have an area of several square inches to about several conditioning circuits .
square feet. As illustrated , conductive elements 202 , 204 Coupling network 210 represents any appropriate net
may be separated from the Earth by a distance x . Distance work of components operable to couple conductive elements
x may be any appropriate distance in which conductive 20 202 , 204 to amplifier 208 . As illustrated , coupling network
elements 202 , 204 may be capable of responding to elec 210 includes a capacitor C1, inductor L1, capacitor C2 and
tromagnetic signals 22 transmitted into the air as a vertical a resistor R arranged as a pi filter. The pi filter generally is
electric field . Conductive elements 202 , 204 may be con - operable to select a desired frequency band for amplifier 208
figured relatively close to the ground . For example , capaci- and to exclude frequencies that may otherwise saturate
tive plates 202 , 204 may be separated from the Earth by 25 amplifier 208 . The resistor may be any appropriate resis
about 10 - 12 inches in particular embodiments . It should be tance , and in some embodiments may be selected to set the
noted , however, that while particular distances are discussed time constant of the input circuitry of electromagnetic
as example , any distance may be used in which conductive signals 22 . Resistor R may be connected across the inputs to
elements 202 , 204 are capable of detecting electromagnetic amplifier 208 in parallel. Moreover, while a particular
signals 22 . Conductive elements 202 , 204 may each be 30 embodiment of coupling network 210 is illustrated , any
connected to inputs of amplifier 208 . conductive element appropriate network components may be used . For example ,
202 or conductive element 204 may also be connected to coupling network 210 may include a matching resistor, a pi
ground . It should be understood, however, that while a filter, a transformer, a resonant network , or any combination
particular embodiment of conductive elements 202 and 204 and number of these components .
is discussed herein , any appropriate conductive elements 35 Shielding 212 represents any suitable electromagnetic
may be used . For example, conductive element 202 may shielding. Shielding 212 may be configured to attenuate
represent a flat conductive plate disposed next to conductive and /or prevent horizontal components of electromagnetic
element 204 , which may be an antenna . Appropriate anten - fields from reaching conducting element 214 . Shielding 212
nas may include flat conductive plates at predetermined may be configured to surround all or a portion of conductive
and/ or fixed distances from the ground , concave conductive 40 elements 202 and 204 . For example , as illustrated , shielding
plates above the ground , multiple conductive plates with 212 may comprise a structure that surrounds the top and
geometry to concentrate the signal , metal screen or grid of sides of conductive elements 202 and 204 . Shielding 212
wire in any appropriate shape and / or geometry , monopole may , for instance, be a cylindrical structure disposed verti
wire extending upwards from the ground, wire looped cally and thatmay be closed on at least one end, such as the
around a ferrite or steel core , or any other appropriate 45 top end . Alternatively , shielding 212 may represent a box or
structure capable of being used as an antenna. Moreover, other appropriate enclosure . Shielding 212 may be made of
conductive elements 202 and 204 may represent any appro - any appropriate material operable to attenuate and/ or pre
priate conductive elements arranged with geometry to maxi- vent electromagnetic signals from propagating through the
mize self capacitance . Also , while illustrated as two com material. For example , shielding 212 may be made of
ponents conductive elements 202 and 204 may be 50 mu-metal, conductive plates or foil, wire mesh , aluminized
implemented as a single component. For example, conduc - Mylar, insulative plates with supplied static charge, and /or
tive elements 202 and 204 may be implemented using a conductive plastic . Mu-metal may refer to one or more
monopole wire extending upward from the ground and /or a classes of nickel-iron alloys that are characterized by a
battery arrangement. In some embodiments, conductive ele - high -magnetic permeability . Shielding 212 may shield
ments 202 and /or 204 may represent a conductive sphere . 55 against static or slowly varying electromagnetic fields that
Amplifier 208 represents any appropriate amplification may otherwise interfere with the detection of electromag
circuit operable to compare signals generated by capacitive netic signals 22 . Shielding 212 may be electrically con
plate 204 to reference signals generated by capacitive plate nected and /or coupled to an input to amplifier 208 . It should
202. Amplifier 208 may , for example , represent an opera - also be understood that in particular embodiments, shielding
tional amplifier . In some embodiments , amplifier 208 may 60 212 may or may not be appropriate and / or necessary.
include any appropriate signal conditioning circuits and /or In operation , electromagnetic signals 22 may be a time
components . For example , amplifier 208 may be capable of varying, vertical electric field . The interaction of electro
performing any one or more of the pre - processing and / or magnetic signals 22 with capacitive plate 204 may produce
processing steps discussed above with respect to FIG . 1 . a charge on conductive elements 204 . The other plate 202
Amplifier 208 may include appropriate inputs and outputs. 65 may be shielded from electromagnetic signals 22 . Accord
As illustrated , capacitive plates 202 , 204 are connected to ingly, signals generate by plate 202 may be interpreted as the
the inputs . The output may be connected to computing reference voltage . Accordingly , a capacitive charge across
 US 9, 759,838 B2
29 30
conductive elements 202 and 204 may result that corre any appropriate distance separating conductive element 214
sponds to electromagnetic signals 22 . In some embodiments, from the surface of the Earth . For example , in a particular
a resistor may be coupled in series with the charged con embodiment, the distance may be about 24 inches. In some
ductive element 202. At appropriate times, the charged embodiments, distance y may be relatively larger than
conductive plate 202 may be discharged and thereby allow 5 distance z .
a time- varying field representative of electromagnetic sig - Electrode 216 represents any appropriate electrical com
nals 22 to be measured , processed , and/ or recorded by ponent configurable to form a connection with the Earth
computing system 30 . By using parallel conductive elements and/ or detect one or more vertical portions of electromag
202, 204, sensor 260 may detect only the vertical compo - netic signals 22. Electrode 216 is configured to form an
nents of electromagnetic signals 22 or other electromagnetic 10 electrical contact with the Earth and may be disposed within
signals. Accordingly , the parallel plate design may be con - the Earth . For example , electrode 216 may be disposed in a
figured not to respond to the horizontal components of hole drilled into the Earth ranging from several inches to
electromagnetic signals 22 . While two conductive elements about 10 feet to about 15 feet. Additionally or alternatively ,
202, 204 are shown, sensor 260 may include a single plate electrode 216 may be disposed within the Earth at varying
appropriately grounded through one or more resistive 15 depths as needed to form an electrical coupling with the
devices and coupled to computing system 30 . Earth . In some embodiments, electrode 216 represents a
FIG . 2B illustrates sensor 262 , which may be a particular porous pot electrode . Porous pot electrodes may include an
embodiment of sensor 26 that includes coupling network appropriate salt and /or aqueous solution to form an electrical
211 , shielding 212 , conductive element 214 , electrode 216 , coupling with the Earth . Suitable salts useful with the
amplifier 218, and signal processing unit 219 . Like sensor 20 electrodes may include , but are not limited to , copper
260 , sensor 262 may be capable of detecting electroseismic sulfate , silver chloride, cadmium chloride ,mercury chloride ,
signals 22 , as previously discussed above with respect to lead chloride , and any combination thereof. In some
sensor 26 . Sensor 260 may also output a signal representing embodiments , electrode 216 may include a conductive elec
detected electromagnetic signals 22 . Sensor 260 may be trode such as rods that are driven into the ground and /or
installed and / or disposed in any appropriate housing, includ - 25 sheets ofmetal,mesh sheets , and /or wires buried in trenches
ing weather-resistant housing, movable vehicles, and /or or in shallow pits . Electrode 216 may be made of a variety
permanent installations , as is discussed above with respect of conductivematerials including, but not limited to , copper,
to sensor 26 . stainless steel, aluminum , gold , galvanized metal, iron , lead,
Coupling network 211 represents any appropriate network brass , graphite , steel, alloys thereof , and combinations
of components operable to couple conductive elements 202, 30 thereof. Electrode 216 may be electrically connected and/or
204 to amplifier 208 . As illustrated , coupling network coupled to shielding 212 and an input to amplifier 218 .
includes a resistor R of an appropriate resistance , which may Electrode 216 may represent a porous pot, a conductive
be selected to set the time constant of the input circuitry of stake, a buried length of wire , a buried wire mesh , and /or a
electromagnetic signals 22 . Resistor R may be connected group of or combination of the aforementioned components .
across the inputs to amplifier 208 in parallel. Moreover, 35 Amplifier 218 and signal processing unit 219 may be
while a particular embodiment of coupling network 211 is similar to amplifier 208 and signal processing unit 209 . As
illustrated , any appropriate network components may be illustrated , an input to amplifier 218 is connected to shield
used . For example , coupling network 211 may include a ing 212 and another input is connected to conductive ele
matching resistor, a pi filter, a transformer, a resonant ment 214 . Coupling network 211 includes a resistor R
network , or any combination and number of these compo - 40 connected across the inputs to amplifier 218 . Electrode 216
nents . is also connected to the input connected to shielding 212 .
Shielding 212 represents any suitable electromagnetic In operation , electromagnetic signals 22 may be a time
shielding , as discussed above with respect to FIG . 2A . varying , vertical electric field . The interaction of electro
Shielding 212 may be configured to surround all or a portion magnetic signals 22 with conductive element 216 may cause
of conducting element 214 . For example, as illustrated , 45 and / or induce an electric response to be conducted and / or
shielding 212 may comprise a structure that surrounds the transmitted to the input to amplifier 218 . Shielding 212 may
top and sides of conducting element 214 . Shielding 212 may attenuate and /or prevent horizontal electromagnetic signals
be electrically connected and / or coupled to an input to from reaching conductive element 214 . Accordingly , the
amplifier 218 . As noted above , it should be understood that signals detected by conductive element 214 may represent a
in particular embodiments , shielding 212 may or may not be 50 stable reference voltage while the signals detected by con
appropriate and/or necessary. ductive element 216 may represent may correspond to
Conductive element 214 represents any appropriate con electromagnetic signals 22 . Amplifier 218 may perform
ductive element operable to generate a stable reference appropriate signal processing and output detected electro
signal shielded from one or more vertical and /or horizontal magnetic signals 22 to computing system 30 . By using
components of electromagnetic signals 22 . Conductive ele - 55 conductive element 214 and shielding 212 , sensor 262 may
ment 214 may represent a conductive plate . As illustrated , detect only the vertical components of electromagnetic
conducting element 214 is a conductive plate that includes signals 22 . Accordingly, the design of sensor 262 may be
multiple folds that form multiple parallel portions of con - such that sensor 262 does not respond to horizontal com
ductive element 214 . Folding conductive element 214 into ponents of electromagnetic signals 22 or other electromag
multiple folded portions may allow conductive element 214 60 netic signals .
to fit within a much smaller volume while also having a FIG . 2C illustrates current sensor 264, which may be a
sufficiently large surface area to detect electromagnetic particular embodiment of sensor 26 that includes shielding
signals 22 . Additionally or alternatively, conductive element 212 , electrode 216 , coupling network 213, resistor 226 ,
214 may include a conductive spine portion that forms a amplifier 228, signal conditioning unit 229 , and battery 230 .
backbone or connection to multiple conductive fins. Con - 65 Sensor 264 may be capable of detecting electroseismic
ductive element 214 may be electrically connected and /or signals 22 may be capable of sensing signals 22 as a current
coupled to an input to amplifier 218 . Distance y represents across a sense resistor 226 . Sensor 260 may also output a
 US 9 ,759,838 B2
31 32
signal representing detected electromagnetic signals 22 . a parallel-plate capacitor antenna comprising two or more
Sensor 260 may be installed and /or disposed in any appro - parallel conducting plates ; a single -plate capacitor antenna
priate housing , including weather - resistant housing , mov comprising one electrode electrically coupled to the earth ; a
able vehicles, and /or permanent installations, as is discussed monopole antenna comprising a conducting element, a
above with respect to sensor 26 . dipole antenna comprising two conducting elements ; a
Shielding 212 represents any suitable electromagnetic multi-pole antenna comprising a plurality of conducting
shielding , as discussed above with respect to FIG . 2A . elements ; a directional antenna comprising conducting ele
Shielding 212 may be configured to surround all or a portion ments arranged to augment a signal amplitude in a particular
of battery 230 . For example , as illustrated , shielding 212 direction , and a coil antenna comprising one or more coils
may comprise a structure that surrounds the top and sides of 10 of wire , and / or any combination of suitable antennas. In
battery 230. Shielding 212 may be electrically connected some embodiments , sensor 26 may represent a concentric
and /or coupled to an input to amplifier 228. In particular electric dipole (CED ). The CED may include two electrodes
embodiments, shielding 212 may additionally or alterna - in a concentric configuration . For example , the electrodes
tively surround all or a portion of coupling network 213. As may be generally circular dipoles with an inner circular
illustrated , shielding 212 surrounds sense resistor 224 of 15 electrode disposed concentrically within an outer circular
coupling network 213. As noted above, it should be under electrode. The electrodes may generally be aligned in a
stood that in particular embodiments , shielding 212 may or plane that is parallel with the plane of the surface of the
may not be appropriate and / or necessary . earth . The CED may then preferentially detect the vertical
Coupling network 213 may include any appropriate com - portion of electromagnetic signals 22 that are substantially
ponents operable to couple battery 230 to amplifier 218 . 20 perpendicular to the plane of the CED . The vertical portion
Coupling network 213 may include similar components as of electromagnetic signals 22 may create a detectable poten
discussed above with respect to FIGS. 2A and 2B . As tial difference between the two electrodes.
illustrated , coupling network 213 includes current sensor In some embodiments , the electromagnetic sensor 26 may
222 and sense resistor 224 . Current sensor 222 represents comprise a pair of electrodes in contact with the earth and
any appropriate current sensor operable to detect a current I 25 disposed within the earth . For example , a first electrode may
generated by electrode 216 . As illustrated , current sensor be disposed in a hole drilled into the earth ranging from
222 is a current transformer that senses current as a voltage about 10 feet to about 15 feet. A second electrode may be
drop across a sense resistor 224 . The current transformer disposed within about 1 foot to about 3 feet of the surface of
may be a step - up transformer with , for example , up to 1000 the earth , and the pair of electrodes may be electrically
times gain or more. Current sensor 222 may represent any 30 coupled . In some embodiments , the pair of electrodes may
appropriate current sensing technologies, including Hall be disposed within the earth at varying depths as needed to
effect sensors, a senseFET, or other appropriate current form an electrical coupling with the earth . In some embodi
sensor. ments, the electrodes may take the form of porous pot
Battery 230 represents any appropriate voltage source electrodes or other electrodes, such electrode 216 . In some
operable to allow current to flow from ground across sense 35 embodiments , the electrodes may comprise a conductive
resistor 224 . Battery 230 may have a large self-capacitance . electrode in contact with the earth and electrically coupled
Charge may leak from ground and attempt to charge battery to a porous pot electrode.
230 . Battery 230 may have a capacitance and /or resistance FIG . 3 is a flowchart illustrating an example method 700
between the battery and ground , which may represent the for processing two or more sources of geophysical survey
capacitance and / or resistance of air. Electrode 216 may be 40 data . Sources of geophysical survey data include passive
connected to a terminal of resistor 224 . Resistor 224 may be electroseismic and seismoelectric surveying 702 , active seis
connected between the terminals of current sensor 222 . One mic surveying 704, microseismology 706 , controlled - source
terminal of resistor 224 may be connected to a terminal of electromagnetic surveying 708 , magnetotelluric surveying
battery 230 . Resistor 226 may be connected in parallel with 710 , magnetic surveying 712 , gravity surveying 714 ,
battery 230 . The outputs of current sensor 222 may be 45 induced polarization 716 , ground -penetrating radar 718 , and
connected to the inputs of amplifier 228 , which may provide various logging technologies including logging (including
an output representing electromagnetic signals 22 . Amplifier SP and/ or acoustic logging ) 720 , airborne surveying 722 ,
228 and signal conditioning unit 229 may be similar to active electroseismic and seismoelectric surveying 724 ,mud
amplifier 208 and signal processing unit 209 . It should be logging 726 , measurement while drilling 728 , geophysical
noted that in some embodiments battery 230 may addition - 50 and / or geological models 730 , passive micro - electric seis
ally or alternatively comprise a capacitor. It should also be mic and seismoelectric surveying 732 , and surface radioac
noted that in some embodiments , a current amplifier may tivity profiling 734 . In general , computing system 30 may be
additionally or alternatively perform the functions of current capable of processing and /or cross correlating two or more
sensor 222, sense resister 224 , and amplifier 228 . available sources of geophysical survey data at step 736 .
In operation , variations in ground potential caused by 55 Processing two or more available sources of geophysical
electromagnetic signals 22 and Earth ' s background electro - data may allow computing system 30 to determine a more
magnetic field 14 may induce a current I across sense accurate and/ or complete identification of various properties
resistor 224 that may be detected by current sensor 222 . of subsurface formation 16 than may otherwise be achiev
Amplifier 228 and /or signal conditioning unit 229 may able by processing a single source of geophysical survey
perform appropriate signal processing and output detected 60 data . For example , computing system 30 may be capable of
electromagnetic signals 22 to computing system 30 . utilizing particular survey methods that have particular
It should be noted , however , that while FIGS . 2A , 2B , and strengths at identifying particular properties , and use those
2C illustrate particular embodiments of sensors 26 , sensors properties as a baseline for comparison and /or correlation
26 may include any appropriate number and combination of with data from other survey methods .
components operable to detect portions of electromagnetic 65 Passive electroseismic surveying 702 may include the
signals 22 , such as various antennas or other sensing ele - method of electroseismic and seismoelectric surveying dis
ments. Suitable antennas may include , but are not limited to , cussed above with respect to FIG . 1. As described in more
 US 9 , 759,838 B2
33 34
detail below , passive survey data detected by, for example, Controlled -source electromagnetic (CSEM ) surveying
sensors 26 and/ or 28 ,may be processed and/ or correlated by 708 may include any appropriate surveying methodology
computing system 30 in order to determine and /or confirm that utilizes a an electromagnetic source of energy and
properties of subsurface earth formation 16 . determine one or more properties of subsurface earth for
Active seismic surveying 704 may include any form of 5 mation 16 . CSEM 708 is particularly useful for providing
seismic surveying that utilizes an active source of seismic presenceelectrical resistivity information that indirectly indicates the
energy to determine one or more properties of subsurface veying 708of hydrocarbons . Utilizing data from CSEM sur
earth formation 16 . Active sources of seismic energy may veying 702, computing system 30 may be/seismoelectric
and passive electroseismic
capable of
sur
deter
include explosives, thumpers , and other man -made or man
controlled formsof seismic energy . Active seismology typi 10 mining both structural and fluid property information
associated with subsurface earth formation 16 . Controlled
cally produces information indicative of geologic structures . source electromagnetic surveying 708 involves the use of a
Seismic prospecting techniques generally involve the use of source of electrical power and a set of electromagnetic
an active seismic energy source and a set of receivers spread receivers . Those electromagnetic receives may be deployed
out along or near the earth 's surface to detect seismic signals 15 on the seafloor in deep water, although land-based applica
reflected from subsurface geological boundaries , such as tions are also possible . Although CSEM surveying 708 may
boundary 18 illustrated in FIG . 1 . These signals are recorded be done on land or in shallow water , recent work finds
as a function of time. Computing system 30 may subse - particularly useful applications in deep water . In CSEM
quently process these signals to reconstruct an appropriate surveying 708 , a power source may drive an electrical
image of the subsurface earth formation 16 . 20 current into the earth that passes through the various sub
In active seismic surveying 704 , seismic energy may surface rock formations. The electrical current follows a
travel from the active source into the Earth , reflect from a path of low electrical resistance through themost conductive
particular geologic layer at a seismic impedance contrast, rock masses. Hydrocarbon reservoirs contain insulating gas
and return to the receiver as a reflected seismic wave . The or oil fluids. Accordingly , the applied electrical current tends
seismic energy may be so - called shear waves (S -waves ) or 25 to flow around resistive reservoir structures. The deflection
so - called compressional waves (P -waves ). Shear waves and of current around reservoirs is detected as a change in
compressional waves differ with respect to their velocities, electromagnetic response on the electromagnetic detectors.
angles of reflection , vibrational directions, and to some The measured signal properties can be processed by com
extent the types of information that may be obtained from puting system 30 to determine the presence of resistive
their respective types of seismic data . However, both types 30 structures that may indicate the presence of hydrocarbons.
of waves suffer similar attenuation by subsurface earth In controlled -source seismoelectric surveying , generally a
formations 16 . Subsurface earth formations 16 tend to seismic source thatmight be dynamite or a seismic vibrator,
attenuate relatively higher frequency components and allow creates a seismic wave that propagates into the subsurface
relatively lower frequency components to pass through the where its seismic energy is partially converted to an electric
earth with relatively little attenuation . For deeper forma- 35 field at a boundary between rock types or at fluid interfaces .
tions , the low frequency content of the reflected seismic The produced electric field then propagates to the surface of
energy may represent information about the underlying the earth where it is detected with electric and /or magnetic
subsurface earth formations 16 . Because of the low fre - field sensors .
quency of the detected reflected seismic energy, however, In controlled -source electroseismic surveying, a source of
the resolution of the reflected seismic energy may be insuf- 40 electrical power is connected to electrodes in contact with
ficient to allow for detection of relatively thin geologic the earth ' s surface. The voltage applied to the electrodes
layers. Passive microseismology 706 , or micro -seismic sur causes electrical current to flow in the subsurface . When that
veying, may refer to any appropriate survey technology that current passes through a rock boundary or a fluid interface ,
detects micro -seismic energy to determine one or more a portion of the electrical energy may be converted to
properties of a subsurface earth formation 16 . Microseis - 45 seismic energy . The resulting seismic energy may then
mology generally relies on small, localized seismic events propagate to the earth 's surface where it is detected with
generated in the earth by naturally occurring earth move - seismic detectors that might be selected from geophones,
ments or by well - drilling operations . Microseismology is accelerometers , or hydrophones .
then a form ofpassive seismic surveying because the source Both seismoelectric and electroseismic conversion ampli
of seismic energy is not generated specifically for the 50 tudes depend on the presence of hydrocarbon fluids so both
purpose of surveying. Such seismic events may be generated methods yield information about rock fluid content that is of
and /or caused by tectonic forces , ocean tides and / or other use in hydrocarbon exploration and production . Both meth
natural phenomena . Seismic waves may also be created ods also yield high resolution images of rock formations that
when drilling or earth fracturing operations are conducted in are typical of seismic surveying. High power sources that
hydrocarbon exploration , production , or in water well ser- 55 may be utilized by CSEM surveying 708 and by active
vices . These natural and man -made events may be referred seismoelectric and electroseismic surveying 722 are typi
to as microseismic events . Generally, micro - seismic survey cally expensive . As a result , the costs of these active -source
ing yields qualitative information about the location of survey methods may tend to limit its commercial viability of
subsurface structures or positional information about drill- CSEM surveying 708 and active - source seismoelectric and
ing operations. In this survey methodology , location of the 60 electroseismic surveying 722 in some environments .
seismic source may be imperfectly known. Accordingly , Magnetotelluric surveying 710 may include any appro
microseismology may be useful to generate high - level infor- priate surveying methodology that utilizes the Earth 's back
mation regarding subsurface earth formation 16 , butmay be ground electromagnetic fields to determine the subsurface
less useful for generating high - resolution images and / or data electrical conductivity of the Earth . Magnetotelluric survey
about subsurface earth formation 16 . In some embodiments , 65 ing 710 may utilize appropriate electromagnetic sensors ,
microseismology may locate the source of fracturing events such as sensors 26 , to detect the low - frequency portion of
such as encountered in fracturing reservoirs. the Earth 's background electromagnetic field . Based on the
 US 9, 759,838 B2
35 36
detected low - frequency signals , computing system 30 may gravitational acceleration . Thus, the presence of high -den
estimate the subsurface electrical conductivity. Magnetotel sity rock may reduce the spatial resolution of the measure
luric surveying 710 may be useful for determining electrical ment and accordingly obscure the presence of a low - density
conductivity , which may be indicative of the types of formation . In addition , the spatial resolution of gravity
materials in subsurface formation 16 , but may be less useful 5 measurements may be generally limited to length scales
for determining detailed location or shape properties of comparable to the depth and lateral extent of the reservoir.
subsurface earth formation 16 . The natural electromagnetic The amplitude of the identifying gravity signature depends
fields detected using magnetotelluric surveying 710 gener
ally originate in the earth 's atmosphere . Naturally - occurring on the volume of the reservoir. Gravity surveying 714 may
electromagnetic fields typically propagate into the subsur- 10 ervoirbestructure
also less useful for determining properties such as res
, pore - fluid properties , or permeability . Grav
face where they encounter rock formations of differing ity and magnetics surveying 712 and /or 714 may be par
electrical conductivity . When the electromagnetic fields con
tact a formation of low conductivity , such as is typical of ticularly useful for surveying large areas, such as whole
hydrocarbon reservoirs, the electromagnetic field measured geological basins .
at the surface of the earth changes. Spatially - dependent 15 Induced polarization ( IP ) surveying 716 may include any
electromagnetic fields measured on the earth 's surface can appropriate methodology for utilizing an induced potential
ctivity forma
be used to indicate the presence of low -conductivity forma field in the Earth to determine one or more properties of
tions that might contain hydrocarbons. Magnetotelluric sur subsurface earth formation 16 . Measuring the induced
veying 710 has several limitations when used alone. Only potential field may allow computing system 30 to determine
low -frequency , long -wavelength electromagnetic stimula - 20 chargeability and resistivity of subsurface earth formation
tion may reach prospective reservoirs because the high - 16 . One or more transmission electrodes may be utilized to
frequency electromagnetic fields are rapidly attenuated by drive and /or induce current into the ground , which may
the conducting earth . Long -wavelength electromagnetic induce a potential field . One or more sensors, such as
waves limit the spatial resolution of magnetotellurics mak potentiometers, may measure the induced potential field .
ing reservoir delineation difficult. Additionally , magnetotel- 25 There are various techniques for IP surveying 716 , including
luric surveying only provides information about formation time- domain based IP surveying and frequency -domain
electrical conductivity and does not yield data revealing based IP surveying . In time-domain based surveying , the
information about porosity , permeability , or reservoir struc transmission electrodes may drive a charge into the Earth for
ture . a specified amount of time. The sensors measure the poten
Magnetic surveying 712 may include any appropriate 30 tial field during the on and off period of the transmission
surveying methodology that utilizes magnetic field sensing electrodes . Based on on - time peak voltage measurements ,
devices to measure the magnetic field of the Earth and the apparent resistivity of subsurface earth formation 16 may
determine one or more properties of subsurface earth for- be calculated by computing system 30 . Based on measure
mation 16 . Magnetic surveying 712 may be particularly ments of the transient voltage decay during the off-time of
suited for surveying from aircraft. Magnetic surveying 712 35 the transmission electrodes , computing system 30 may cal
may be based on the fact that hydrocarbon reservoirs and culate chargeability .
mineral deposits, such as iron ore , may alter the local earth ’s Ground -penetrating radar (GPR ) surveying 718 may
magnetic field . Accordingly, computing system 30 may include any appropriate surveying methodology that uses
process data received from magnetic field sensing devices in ground -penetrating radio waves to determine one or more
combination with passive electroseismic and seismoelectric 40 properties of subsurface earth formation 16 . The radio waves
surveying 702 to determine the presence of reservoir struc - may be electromagnetic waves in the microwave band of the
tures and/ or the presence of hydrocarbons and other miner radio spectrum . Transmitters may generate high - frequency
als . Magnetic surveying 712 may have several limitations radio waves and transmit the radio waves into the Earth .
when used alone . Magnetic surveying 712 may be less Antennas or appropriate sensing elements may detect a
useful for determining and /or measuring properties related 45 return signal reflected from subsurface earth formation 16 .
to the reservoir spatial extent and structure of subsurface When the generated radio wave hits an object or boundary ,
earth formation 16 . Magnetic surveying 712 also may not be such as boundary 18 with differing dielectric constants , the
capable of identifying particular fluids and / or minerals or receiving antenna receives variations in the reflected return
fluid flow properties . signal. Those variations may be processed by computing
Gravity surveying 714 may include any appropriate sur- 50 system 30 to identify structural features of the subsurface .
veying methodology that utilizes gravity detectors to deter - The penetration depth ofGPR surveying 718 may generally
mine one or more properties of subsurface earth formation be limited by the electrical conductivity of the ground
16 . Reservoirs such as subsurface earth formation 16 typi- beneath the transmission signal. As conductivity decreases,
cally have smaller mass density than non - reservoir rock . A signal depth may increase . Accordingly, GPR surveying 718
gravity meter of sufficient sensitivity may be capable of 55 may be particularly useful for low - conductivity ground
detecting the difference in mass density of subsurface earth types , such as ice , dry sandy soils, granite, limestone, and
formation 16 as compared to surrounding formations. Com - concrete . In high -conductivity ground types, GPR surveying
puting system 30 may determine the presence of subsurface 718 may only penetrate a few meters. Even in low - conduc
earth formation 16 based on receiving data from a gravity t ivity materials, GPR surveying 718 may be particularly
meter indicating a minimum in local gravitational accelera - 60 useful for identifying features that are only up to several
tion over subsurface earth formation 16 . Gravity surveying hundred meters in depth . Accordingly, GPR surveying 718
714 may have several limitations when used alone . For may be utilized by computing system 30 to identify prop
example , local gravity values reflect an average of themass erties of near-surface formation 24, such as objects, changes
densities from all materials in the neighborhood of the in materials , voids, cracks, and the presence and amount of
gravity detector. Accordingly, while reservoirs of low den - 65 ground water and other fluids . GPR surveying 718 may also
sity reduce the measured gravitational acceleration , the be useful for identifying and /or tracking pollutants and
presence of high - density rock may increase the measured contaminants.
 US 9 ,759,838 B2
37 38
Logging 720 may include any appropriate logging tech reservoir properties but may guide the locations where
nique, including acoustic and/ or spontaneous potential log - high -resolution surveys such as seismology and electroseis
ging. Logging 720 may include passive logging techniques mology may be useful. Accordingly , another survey , such as
such as spontaneous potential (SP ) logging to measure a passive electroseismic/seismoelectric survey 702 , may be
resistivity and / or conductivity of the surrounding formation 5 initiated in response to information about subsurface forma
In particular, SP logging 720 may include any appropriate tion 16 gleaned from airborne surveying 722 .
surveying methodology that uses passive measurements to Mud logging 726 may include any appropriate method
determine electrical potentials between various depths in a ology for detecting the properties of the drilling cuttings
well-bore . SP logging 720 is a technique that may generally created during drilling a hole for hydrocarbon exploration or
be utilized by well- loggers during drilling operations. One 10 other purposes .Mud logging 726 may determine the type of
or more sensors , such as potentiometers , may measure rock penetrated by the drill bit, the presence ofhydrocarbon
electric potentials between depths in a well -bore and a or water in the cuttings, radio activity that is an indicator of
grounded voltage at the surface . Changes in electrical poten - hydrocarbons or shales , and microscopic rock properties
tial may be caused by a build -up of charge in the well bore related to porosity and permeability .
walls. The well-bore may include conductive fluids to facili- 15 Measurement while drilling 728 may include any meth
tate a SP response . SPs may occur when two aqueous odology suitable for detection of subsurface properties near
solutions that have different ionic concentrations are placed the drill bit and/ or changes in subsurface formations caused
in contact through a porous , semi-permeable membrane . by drilling operations such as fracturing and flowing fluids .
Ions tend to migrate from high to low ionic concentrations. These properties may include but are not limited to acoustic
In the case ofSP logging 720 , two ormore aqueous solutions 20 properties, electrical properties, fracture properties, drill bit
may be the conductive fluid in the well bore, such as drilling location , formation pressure , porosity , and permeability .
mud, and the water in a subsurface earth formation 16 . Geological and geophysical models 730 may include
Whether the conductive fluid containsmore or less ions than information generated by studying the geological history ,
the formation water may cause the SP to deflect opposite a the present day setting, analogies to near sites, and experi
permeable subsurface earth formation 16 . Measurements of 25 ence gained by measurements on many geological forma
SP may be utilized by computing system 30 to detect the tions. Such models may offer guidance to reduce the risk in
presence of hydrocarbons, which may reduce the response finding and developing subsurface resources .
on an SP log due to the reduction of contact between the Passive micro - seismoelectric and micro - electroseismic
conductive fluid in the well -bore and contact with formation surveying 732 may include any methodology suitable for
water. SP logging 720 may be utilized to determine locations 30 detecting electromagnetic and /or seismic emanations from
and/ or depths of permeable subsurface earth formation 16 . passive , naturally - occurring, and/ or man -made seismic and/
the boundaries of subsurface earth formation 16 , formation or electromagnetic sources of energy below the Earth 's
water resistivity , and other properties . Measurements of SP surface . Microseismology 706 may detect seismic events
may be utilized by computing system 30 to determine the originating at depth as discussed above, while passive
location of potential gradients where electroseismic and/ or 35 micro - seismoelectric and micro - electroseismic surveying
seismoelectric conversions are likely to occur. Computing 732 may take advantage of the combined use of both the
system 30 may then determine depths where signals 20 electromagnetic field and the seismic energy generated by
and / or 22 signals are correlated with SP amplitudes. Log - subsurface events . For example , earthquakes, tidal motion ,
ging 720 may additionally or alternatively include active and tectonic forces generate both electromagnetic and seis
source logging . For example , active source logging may use 40 mic sources of energy . Such events are known to generate
an active source such as a nuclear source and an associated seismic and electromagnetic energy . These events may also
sensor . One example nuclear source may include thorium or generate secondary electromagnetic and seismic signals
other gamma emitting materials. caused by electroseismic and seismoelectric conversions.
Other logging methods 720 may include conductivity Microseismic events created during well-drilling operations,
logging, acoustic logging, dielectric constant logging , 45 formation fracturing, fluid production , and fluid migration
gamma ray logging , formation tester logging ,microresistiv are of particular importance in hydrocarbon production and
ity or imaging logging , density, neutron porosity , sonic , exploration , and in aquifer development. It is known that
caliper, and nuclear magnetic resonance logging. Generally, formation fracturing and fluid flow in the subsurface create
computer system 30 may use logging data individually seismic events that are of use in locating the drill bit ,
and / or in correlative fashion to determine subsurface rock 50 analyzing fracture development and in detecting fluid migra
and fluid properties . In combination with passive electro - tion . Microseismic monitoring 706 may be limited by the
seismic and seismoelectric detection 702, logging data from uncertain location of the source signal and by uncertainty in
single logs or in combination with several or many logs 720 , the seismic properties of the subsurface, particularly the
computer 30 may determine the structural and fluid proper - velocity of seismic waves in the subsurface . Micro - electro
ties of subsurface formations, particularly those containing 55 seismology and micro -seismoelectric methods 732 may
hydrocarbons. overcome these limitations on microseismology.
Airborne surveying 722 may include any appropriate In one embodiment, fracture events and drill-bit noise
surveying methodology that uses airplanes , helicopters , or generated during drilling and / or hydraulic fracturing may
lighter- than - air means for deploying geophysical surveying generate both seismic waves and electromagnetic energy
detectors . Detectors may include but are not limited to 60 that propagate to the surface of the earth and /or to the
gravity , electric field , magnetic field , electromagnetic field , location of wells . The electromagnetic propagation is known
video , infrared , ultraviolet, and other sensors in the electro - to travel at a speed that is much larger than the seismic wave .
magnetic spectrum . Airborne surveys 722 may generally Detection of the arrival of the EM wave ahead of the seismic
cover large areas of the Earth ' s surface. Accordingly , par - wave can then permit analysis of the seismic travel time and
ticular airborne survey methods 722 may achieve only lower 65 may permit more accurate determination of the depth to the
spatial resolution as compared to other survey methods. origin of the seismic signal. The detection of such electro
Such surveys are not generally used for detailed analysis of magnetic and seismic energies may be conducted on the
 US 9 ,759,838 B2
39 40
surface of the earth , in shallow holes or in wells . The a gravity survey 714 , magnetic survey 712 , IP survey 716 ,
detection means may be seismic detectors such as geo and /or GPR survey 718 may be conducted based on an
phones , hydrophones in wells , accelerometers , digital accel- indication of a fluid present in the subterranean formation of
erometers as well as antennas designed to detect the elec interest. Alternatively or in addition , passive electroseismic
tromagnetic energy . 5 surveying 702 may be performed based on data from any of
In another embodiment, the seismic and/ or electromag - the survey methods described herein being processed by
netic waves generated by drilling and / or fracturing activities computing system 30 to identify a property of subsurface
may further generate secondary electromagnetic and seismic earth formation 16 of interest for further exploration and /or
energies through electroseismic and / or seismoelectric con - surveying. Passive electroseismic surveying 702 may thus
versions . Detecting these secondary EM and seismic fields 10 be utilized as a precursor to additional surveying method
may advantageously improve the analysis of the location of ologies to provide an initial analysis to identify regions of
subsurface structures 16 as well as the location and probable interest for additional surveying. Additionally or alterna
identity of pore fluids. Computing system 30 may process tively passive surveying 702 may be used after those meth
micro - electroseismic and micro -seismo- electric data con - odologies are employed to obtain more detailed information
currently or in sequence with passive electroseismic and 15 about a region of interest surveyed using another technique .
seismoelectric data to locate the microseismic events within In some embodiments, passive electroseismic surveying 702
the larger structure of interest 16 . may be utilized during the same surveying operation in
In another embodiment, the seismic and / or electromag - conjunction with other survey methods. Passive electroseis
netic waves generated by drilling and/ or fracturing activities mic surveying 702 may be utilized at the same time and/ or
may further generate secondary electromagnetic and seismic 20 during intervals in which other survey methods are not being
energies through electroseismic and /or seismoelectric con utilized . For example , passive electroseismic surveying 702
versions that propagate to additional geological structures at may be capable of detecting signals 20 and/or 22 during
greater depth or at distances far from the signal origin . For periods in which a response signal generated by an active
example , a seismic wave created by drilling and /or fractur- source of seismic energy during an active seismic surveying
ing activity may propagate to a greater depth where seismic 25 704 operation is reduced and/ or attenuated . Alternatively or
reflection and / or seismoelectric conversion occur. The then in addition , computing system 30 may be capable of filtering
generated secondary event may propagate to the surface or sources of active seismic energy and detect signals 20 and/ or
a well location where it may be detected . The secondary 22 during active seismic survey 702 operations . The addi
wave field may then be useful in creating an image of the tional passive electroseismic survey 702 may provide for
deep structure . Alternatively or in addition to the secondary 30 more data over a greater number of sensors and /or detectors
conversion event may occur at a distant location from the to obtain higher quality information about the subterranean
source event at a depth similar to the source depth or earth formation 16 than other survey methods. Thus,method
shallower than the source event. Such secondary conver - 700 may be utilized by computing system 30 as described
sions may advantageously generate signals useful in iden - herein in combination with other surveying techniques to
tifying additional structures 16 and /or may, after signal 35 provide information about a subterranean earth formation
processing in computer 30, identify fluids such as hydro - 16 . Particular embodiments and correlation techniques for
carbon fluids. combinations of various surveymethodologies are discussed
Surface radioactivity profiling 734 may include any below with respect to FIGS. 4 - 7 . In some embodiments,
appropriate surface radioactivity profiling technique , such as passive electroseismic surveying 702 may be used alone or
surface gamma ray surveying . For example , some subsur- 40 in conjunction with other survey methods to determine a
face earth formations 16 may exhibit a chimney effect in location at which to drill and /or commence one or more
which fluids or minerals may seep to the surface . This wellbores into subsurface earth formation 16 . For example ,
seepage may cause radioactive changes at the surface that computing system 30 may , as described above , detect an
can be detected through the use of surface radioactivity envelope using passive electroseismic surveying 702 that
profiling 734 . 45 indicates the presence of one or more hydrocarbons in
Computing system 30 may, at step 736 , process survey subsurface earth formation 16 . Based on the envelope,
data from two or more sources of geophysical survey data , computing system 30 may determine a drilling operation can
including two or more of passive electroseismic surveying or should be undertaken at a particular location relative to
702, active seismic surveying 704 , microseismology 706 , subsurface earth formation 16 . Additionally or alternatively ,
controlled -source electromagnetic surveying 708 , magneto - 50 passive electroseismic surveying 702 may be used alone or
telluric surveying 710 , magnetic surveying 712 , gravity in conjunction with other survey methods to determine
surveying 714 , induced polarization 716 , ground -penetrat- locations at which to commence any other appropriate
ing radar 718 , logging 720 , airborne surveys 722, active mining operation as appropriate to recover the particular
electroseismic and seismoelectric surveying 724 , mud log- type of mineral, which may also be based on the depth ,
ging 726 , measurement while drilling 728, geological mod - 55 geologic surface features, and /or surrounding formations in
eling 730 , passive micro -seismoelectric and micro -electro the subsurface .
seismic surveying 732 , and surface radioactivity profiling FIG . 4 is a perspective diagram illustrating an example
734. For example , by utilizing data from passive electro surveying system 400 utilizing passive electroseismic and
seismic surveying 702 in conjunction with data from various seismoelectric surveying 702 techniques and active seismic
other survey methods, disadvantages and limitations of the 60 surveying 704 techniques, which explained above, may
other survey methods may be reduced and/or eliminated include active electroseismic and seismoelectric surveying
In some embodiments ,more information may be obtained techniques. As illustrated system 400 includes electromag
about the subterranean formation by conducting one or more netic sensors 26 , seismic sensors 28 , computing system 30
additional surveys before , after, or during any of the passive which have been described above with respect to FIG . 1 and
electroseismic surveying 702 techniques described herein 65 may operate in a similar manner as described above with
have been carried out. For example , an active seismological respect to system 10 . In addition , system 400 may include
survey 704 , a microseismic survey 706 , CSEM survey 708 , one or more active seismic generators 42 and sensors 28 may
 US 9, 759,838 B2
41 42
be further and /or alternatively capable of detecting a seismic active source 42 in order to determine the various properties
response generated by active seismic sensor 42 . In addition , of subsurface earth formation 16 based on those active
one or more active sources of electromagnetic energy may seismic signals .
be located in the vicinity of a surveying operation . Accord Computing system 30 may be capable of correlating data
ingly , electromagnetic sensors 26 and/or sensors 28 may be 5 received as a result of passive electroseismic or seismoelec
capable of detecting one or more signals 20 , 22 , as discussed tric surveying 702 and / or data received as a result of seismic
above, and may be additionally or alternatively capable of by surveying 704 . For example , seismic data may be analyzed
detecting one or more electromagnetic signals generated as boundary computing system 30 to determine a depth of a specific
a response to electromagnetic source as a result of an 10 Once such 18features or other feature of subsurface formation 18 .
electroseismic or seismoelectric conversion in subservice as a baseline in theareanalysis identified , those features may be used
of passive survey data . Depth
earth formation 16 . In general, system 400 may be capable information from active seismic
of utilizing any one or more of the passive electroseismic ments , be used as an assumptionsurveying of
, in some embodi
depth when utilizing
and seismoelectric surveying 702 techniques and / or active passive seismic surveying . For example , depth information
seismic surveying 704 techniques described abovee .. InIn addi
addi- 15 obtained as a result of seismic surveying 704 may be utilized
tion, computing system 30 may be capable of correlating in the frequency depth function discussed above with respect
data from passive electroseismic surveying 702 with data to FIG . 1 in order to determine a baseline depth from which
detected by active seismic surveying method 704 as will be other depths and / or other features of subsurface formation
described in more detail below . 16 utilizing passive surveying technique 702 may be deter
As discussed above , an active electromagnetic source 20 mined . Alternatively or in addition, data from both survey
may include any manmade or other active source of elec techniques may be formatted and/or integrated into a single
tromagnetic energy detectable by electromagnetic sensors data set and the combined data may be analyzed to identify
26 and/or seismic sensors 28 . Electromagnetic source may properties of subsurface formation 16 .
include a source of electromagnetic energy capable of gen - As a result, by utilizing multiple surveying techniques,
erating an electromagnetic response signal 20 or seismic 25 additional information regarding subsurface 16 may be
signal 22 in a similar manner as discussed above with obtained than would otherwise be available utilizing active
respect to passive electromagnetic source 12 . seismic surveying 704 alone. For example , seismology
Active seismic source 42 may represent any appropriate technique 702 may provide structural information regarding
active source of seismic energy 44 including thumpersin, 30 subsurface earth formation 16 while passive electroseismic
surveying 702 may provide structural and electrical proper
dynamite , vibrators or other sources of manmade seismic su ties related to the presence of hydrocarbons. Data from both
energy . Seismic sensors 28 may be configured to detect techniques may be capable of confirming the presence of
active response signals generated by active seismic source hydrocarbons or other minerals . In addition , the combination
42 . In some embodiments , seismic sensors 28 may be of the two survey techniques may provide the ability to
capable of detecting both response signals from active 35, identify more readily stratographic traps, meandering
seismic source 42 and signals 20 . Alternatively, particular streams and other irregular subsurface earth formation 16
seismic sensors 28 may be configured to detect one type of which may contain hydrocarbons or other minerals of inter
signal or the other. est.
In operation , computing system 30 may be capable of FIG . 5 is a perspective drawing illustrating an example
utilizing active seismic sources 42 and seismic sensors 28 to 40 surveying system 500 utilizing passive electroseismic and
perform active seismic surveying 704 . In addition , comput - seismoelectric surveying 702 techniques and magnetotellu
ing system 30 may utilize sensors 26 and/ or sensors 28 to ric surveying 710 . As illustrated , system 500 includes elec
perform passive electroseismic and seismoelectric surveying tromagnetic sensors 26 , seismic sensors 28 , computing
702. Computing system 30 may be capable of utilizing these system 30 , which are described above with respect to FIG .
techniques in any suitable manner. For example , computing 45 1 and may operate in a similar manner as described above
system 30 may primarily utilize active seismic surveying with respect to system 10 . As illustrated , system 500 may
704 to detect seismic data which may reveal structure , depth , also include electromagnetic sensors 64 which may be
and location of subsurface formation 16 . During periods in capable of detecting magnetotelluric signals, which are
which response signals generated by active source 42 are described above with respect to FIG . 3 . While not illustrated ,
reduced and/ or attenuated , computing system 30 may 50 in some embodiments , system 600 may also include a
receive signals 20 and / or 22 detected by sensors 26 and/ or controlled source of electromagnetic radiation which may be
28. For example, computing system 30 may utilize sensors either generated by vehicle 50 and /or generated by various
26 and / or 28 between the seismic events generated by active electrodes which may be disposed on the ocean floor or other
seismic source 42 . appropriate location . System 500 may additionally or alter
Additionally or in the alternative , computing system 30 55 natively include appropriate components for performing IP
may be capable of detecting signals 20 and 22 at substan - surveying 716 .
tially the same time or at overlapping times during which Electromagnetic sensor 64 may be capable of detecting
active source 42 is generating seismic signals 44 . In such magnetotelluric signal 62 . Electromagnetic sensor 64 may
embodiments, computing system 30 may include appropri- be similar to any one of the embodiments of sensors 26
ate filters to remove the signals generated by active seismic 60 discussed above and operating to discuss to detect electro
source 42 using any appropriate technique including predic - magnetic signal 62 . Sensor 64 may be configured to detect
tive filtering in a similar manner as discussed above . In such horizontal components of the earth 's background electro
embodiments, passive electroseismic or seismoelectric data magnetic field 64 which are useful for processing by com
may treat the signals generated by seismic source 42 as puting system 30 in magnetotelluric surveying 710 .
noise . Accordingly, those signals may be filtered from those 65 In operation , system 500 may utilize magnetotelluric
data while a separate processing task may actively process surveying 710 , passive electroseismic or seismoelectric sur
response signals generated as a result of signals 44 from veying 702 and /or CSEM 708 in order to determine prop
 US 9 ,759,838 B2
43 44
erties of subsurface earth formation 16 . In addition or in the surveying 702 . In some embodiments, computing system 30
alternative, various correlation techniques may be utilized to may additionally be capable of correlating and processing
correlate data between the various survey methods. For data received as result of magnetotelluric surveying 710 . As
example, magnetotelluric surveying 710 may be utilized by a result, by utilizing multiple surveying techniques , addi
computing system 30 to confirm electrical conductivity , 5 tional information regarding subsurface 16 may be obtained
which may be indicative of the types of materials in sub - than would otherwise be available utilizing CSEM tech
surface formation 16 . Passive electroseismic surveying 702 niques 708 or magnetotelluric surveying 710 alone . For
may provide well-tested geometry . Data from both tech - example , CSEM surveying 708 may be utilized by comput
niques may be capable of confirming the presence of hydro - ing system 30 to confirm high electrical resistivity which
carbons or other minerals . In addition , the combination of 10 may be utilized to indicate the presence of subsurface earth
the two survey techniques may provide the ability to identify formation 16 . Passive electroseismic surveying 702 may
more readily stratographic traps , meandering streams and provide well -tested geometry . Data from both techniques
other irregular subsurface earth formation 16 which may may be capable of confirming the presence of hydrocarbons
contain hydrocarbons or other minerals of interest . or other minerals. In addition , the combination of the two
FIG . 6 is a perspective drawing illustrating an example 15 survey techniques may provide the ability to identify more
surveying system 600 utilizing passive electroseismic and readily stratographic traps , meandering streams and other
seismoelectric surveying 702 techniques and CSEM survey - irregular subsurface earth formation 16 which may contain
ing 708 . As illustrated , system 600 includes a vehicle 50 hydrocarbons or other minerals of interest.
which may be capable of operating in water, including deep FIG . 7 is a perspective drawing illustrating an example
water operations. Vehicle 50 may be capable of towing or 20 surveying system 700 utilizing passive electroseismic and
pulling electrodes 52 , sensors 26 , and /or sensors 64 . Sensors seismoelectric surveying 702 techniques and SP logging 720
26 which may be capable of detecting electromagnetic techniques. As illustrated , system 700 includes sensors 26
signals generated by subsurface formation 16 , which may be and 28 , logging facility 50 and potentiometer 72 which may
at some distance below the floor of the body of water . be disposed in a well bore of a drilling operation 70 .
Sensors 64 may be capable of detecting magnetotelluric 25 Logging facility 50 may include computing system 30 and
signals 62 . In some embodiments , sensors 26 may addition - other equipment appropriate for logging drilling operation
ally or alternatively be disposed on the seafloor and /or bed 70 , including the ability to process signals received from
of a body of water. Electromagnetic sensors 64 and/ or potentiometer 72 . Survey data received as a result of SP
sensors 26 may be capable of transmitting information logging by detecting the potentiometer 72 may be correlated
wirelessly to computing system 30 , which may be located on 30 with passive survey data received by sensors 26 and /or 28 .
vehicle 50 . Additionally or alternatively, sensors 64 and/ or For example , SP logging data may provide extremely reli
sensors 26 may store information locally and /or may be able depth and /or resistivity information for subsurface earth
retrieved by vehicle 50 . Electrodes 52 may be used to formation 16 which may be used as a baseline in processing
generate a high current signal that may be transmitted into signals received from sensors 26 and /or 28 according to
the Earth through the body of water. Computing system 30 35 passive survey methods 702 . Data from both techniques may
may be housed in vehicle 50 or other structure capable of be capable of confirming the presence of hydrocarbons or
holding power transformers and other power generation other minerals . In addition , the combination of the two
equipment capable of generating the appropriate amount of survey techniques may provide the ability to identify more
current required to penetrate the Earth using electrodes 52 . readily stratographic traps, meandering streams and other
Electrodes 52 may include positive electrode 52A and 40 irregular subsurface earth formation 16 which may contain
negative electrode 52B . Electrodes 52 may be of any appro - hydrocarbons or other minerals of interest.
priate length and arranged in any appropriate manner with FIG . 8 is a flowchart illustrating an example method 800
respect to the Earth capable to generate a source of current for correlating data received from various geophysical sur
that can penetrate into the Earth . For example , a current may vey methods. Method 800 begins in step 802 at which first
be induced to flow into the Earth from negative electrode 45 signals are received from first sensor elements . For example ,
52B and return from the Earth to positive electrode 52A . The signals 20 and /or 22 may be detected by sensors 26 and /or
current may be modulated by subsurface formation 16 . 28 and transmitted to computing system 30 . At step 804 ,
Accordingly , sensors 26 may be capable of detecting a computing system 30 may process the signals according to
modulation caused by subsurface formation 16 within the passive survey method 700 using any of the techniques
signals returned to electrode 52A . 50 discussed above . At step 806 , computing system 30 may
In operation , computing system 30 may be capable of receive additional signals from second sensor elements . For
utilizing electrodes 52 to perform CSEM surveying 708 . In example , computing system 30 may receive signals gener
addition , computing system 30 may utilize sensors 26 and /or a ted as a result of any of the aforementioned survey tech
sensors 28 to perform passive electroseismic and seismo niques including any one or more of the survey methods
electric surveying 702 . Computing system 30 may be 55 described above with respect to FIG . 3 .
capable of utilizing these techniques in any suitable manner. At step 808 , computing system 30 may process those
For example , computing system 30 may primarily utilize signals according to the particular survey method associated
CSEM surveying 708 to detect electromagnetic survey data . with those signals . At step 810 , computing system 30 may
During periods in which response signals from electrodes 52 determine whether additional survey method data are avail
are reduced and /or attenuated , computing system 30 may 60 able and may then utilize those additional methods to
receive signals 20 and /or 22 detected by sensors 26 and /or receive additional signals from other sensor elements at step
28 . For example, computing system 30 may utilize sensors 806 after which those signals may be processed at step 808.
26 and /or 28 between the times in which currents are Accordingly , computing system 30 may be capable of pro
generated by electrodes 52 . actively utilizing available survey methods when configured
Computing system 30 may be capable of correlating and 65 to use those methods . For example , during an active survey
processing survey data received as a result of CSEM tech - operation 704 , computing system 30 may be configured to
niques 708 and passive electroseismic and seismoelectric automatically initiate signals received from sensors 26 and /
 US 9 ,759,838 B2
45 46
or 28 during periods in which the active survey signals from selected for execution . The ROM 986 is used to store
active source 42 are attenuated and /or negligible , as dis - instructions and perhaps data which are read during program
cussed above . execution . ROM 986 is a non -volatile memory device which
At step 812 , computing system 30 may be capable of typically has a small memory capacity relative to the larger
correlating any of the received signals according to any of 5 memory capacity of secondary storage 984 . The RAM 988
the above survey methods including any of the aforemen is used to store volatile data and perhaps to store instruc
tioned correlation techniques discussed with respect to tions. Access to both ROM 986 and RAM 988 is typically
FIGS. 1 - 7 . At step 814 , various subsurface properties may be faster than to secondary storage 984. The secondary storage
determined based on individual surveymethods alone and /or 984 , the RAM 988 , and / or the ROM 986 may be referred to
based on the correlation of the received signals performed at 10 in some contexts as computer readable storage media and / or
step 812 . After step 814 is performed , computing system 30 non -transitory computer readable media .
may perform any other appropriate computing task such as I/O devices 990 may include printers, video monitors ,
generating and / or updating three dimensional, four dimen - liquid crystal displays (LCDs), touch screen displays , key
sional or two dimensional models of subsurface earth for boards, keypads , switches, dials, mice , track balls , voice
mation 16 . For example , computing system 30 may gradu - 15 recognizers , card readers, paper tape readers, or other well
ally move over time in order to take large amounts of data , known input devices .
samples or particular areas which may be very large in The network connectivity devices 992 may take the form
comparison with the extent of the area that is capable of of modems, modem banks , Ethernet cards, universal serial
being surveyed by an array of sensors at any one location . bus (USB ) interface cards, serial interfaces , token ring cards ,
FIG . 9 illustrates an example computer system 30 suitable 20 fiber distributed data interface (FDDI) cards , wireless local
for implementing one or more embodiments disclosed area network (WLAN ) cards, radio transceiver cards such as
herein . The computer system 30 includes a processor 982 code division multiple access (CDMA ), global system for
(which may be referred to as a central processor unit or mobile communications (GSM ), long - term evolution (LTE ),
CPU ) that is in communication with memory devices includ - worldwide interoperability for microwave access (Wi
ing secondary storage 984 , read only memory (ROM ) 986 , 25 MAX ), and /or other air interface protocol radio transceiver
random access memory (RAM ) 988 , input/output (I/ O ) cards , and other well -known network devices. These net
devices 990 , and network connectivity devices 992 . The work connectivity devices 992 may enable the processor 982
processor may be implemented as one or more CPU chips. to communicate with the Internet or one or more intranets .
It is understood that by programming and/ or loading With such a network connection , it is contemplated that the
executable instructions onto the computing system 30 , at 30 processor 982 might receive information from the network ,
least one of the CPU 982, the RAM 988 , and the ROM 986 or might output information to the network in the course of
are changed , transforming the computing system 30 in part performing the above- described method steps . Such infor
into a particular machine or apparatus having the novel mation , which is often represented as a sequence of instruc
functionality taught by the present disclosure . It is funda - tions to be executed using processor 982 , may be received
mental to the electrical engineering and software engineer - 35 from and outputted to the network , for example , in the form
ing arts that functionality that can be implemented by of a computer data signal embodied in a carrier wave .
loading executable software into a computer can be con - Such information , which may include data or instructions
verted to a hardware implementation by well known design to be executed using processor 982 for example , may be
rules . Decisions between implementing a concept in soft received from and outputted to the network , for example , in
ware versus hardware typically hinge on considerations of 40 the form of a computer data baseband signal or signal
stability of the design and numbers of units to be produced embodied in a carrier wave . The baseband signal or signal
rather than any issues involved in translating from the embodied in the carrier wave generated by the network
software domain to the hardware domain . Generally, a connectivity devices 992 may propagate in or on the surface
design that is still subject to frequent change may be of electrical conductors, in coaxial cables, in waveguides, in
preferred to be implemented in software , because re - spin - 45 an optical conduit , for example an optical fiber, or in the air
ning a hardware implementation is more expensive than or free space . The information contained in the baseband
re -spinning a software design . Generally , a design that is signal or signal embedded in the carrier wave may be
stable that will be produced in large volume may be pre - ordered according to different sequences, as may be desir
ferred to be implemented in hardware , for example in an able for either processing or generating the information or
application specific integrated circuit (ASIC ), because for 50 transmitting or receiving the information . The baseband
large production runs the hardware implementation may be signal or signal embedded in the carrier wave , or other types
less expensive than the software implementation . Often a of signals currently used or hereafter developed , may be
design may be developed and tested in a software form and generated according to several methods well known to one
later transformed , by well known design rules , to an equiva - skilled in the art. The baseband signal and/ or signal embed
lent hardware implementation in an application specific 55 ded in the carrier wave may be referred to in some contexts
integrated circuit that hardwires the instructions of the as a transitory signal.
software . In the samemanner as a machine controlled by a The processor 982 executes instructions , codes, computer
new ASIC is a particular machine or apparatus , likewise a programs, scripts which it accesses from hard disk , floppy
computer that has been programmed and /or loaded with disk , optical disk (these various disk based systemsmay all
executable instructions may be viewed as a particular 60 be considered secondary storage 984), ROM986 , RAM 988 ,
machine or apparatus. or the network connectivity devices 992. While only one
The secondary storage 984 is typically comprised of one processor 982 is shown,multiple processors may be present.
or more disk drives or tape drives and is used for non Thus, while instructions may be discussed as executed by a
volatile storage of data and as an over -flow data storage processor, the instructions may be executed simultaneously ,
device if RAM 988 is not large enough to hold all working 65 serially , or otherwise executed by one or multiple proces
data . Secondary storage 984 may be used to store programs sors . Instructions , codes, computer programs, scripts , and /or
which are loaded into RAM 988 when such programs are data that may be accessed from the secondary storage 984 ,
 US 9 ,759,838 B2
47 48
for example , hard drives , floppy disks, optical disks , and /or 986 , to the RAM 988 , and /or to other non -volatile memory
other device, the ROM 986 , and /or the RAM 988 may be and volatile memory of the computing system 30 .
referred to in some contexts as non -transitory instructions In some contexts , a baseband signal and / or a signal
and /or non -transitory information . embodied in a carrier wave may be referred to as a transitory
In some embodiments , computing system 30 may com - 5 signal. In some contexts , the secondary storage 984, the
prise two or more computers in communication with each ROM 986 , and the RAM 988 may be referred to as a
other that collaborate to perform a task . For example , but not non -transitory computer readable medium or a computer
by way of limitation , an application may be partitioned in RAM readable storage media . A dynamic RAM embodiment of the
such a way as to permit concurrent and /or parallel process 988 , likewise , may be referred to as a non -transitory
ing of the instructions of the application . Alternatively , the 10 computer
receives
readable medium in that while the dynamic RAM
electrical power and is operated in accordance with
data processed by the application may be partitioned in such its design , for example during a period of time during which
a way as to permit concurrent and/ or parallel processing of the computer 980 is turned on and operational, the dynamic
different portions of a data set by the two or more computers . RAM stores information that is written to it . Similarly , the
In some embodiments, virtualization software may be
employed by the computing system 30 to provide the 15 processor 982 may comprise an internal RAM , an internal
ROM , a cache memory, and / or other internal non - transitory
functionality of a number of servers that is not directly storage blocks, sections, or components thatmay be referred
bound to the number of computers in the computing system to in some contexts as non -transitory computer readable
30 . For example , virtualization software may provide twenty m edia or computer readable storage media .
virtual servers on four physical computers. In some embodi- 20 Herein , “ or ” is inclusive and not exclusive , unless
ments , the functionality disclosed above may be provided by expressly indicated otherwise or indicated otherwise by
executing the application and /or applications in a cloud context. Therefore, herein , “ A or B ” means " A , B , or both ,”
computing environment. Cloud computing may comprise unless expressly indicated otherwise or indicated otherwise
providing computing services via a network connection by context.Moreover, " and” is both joint and several, unless
using dynamically scalable computing resources. Cloud 25 expressly indicated otherwise or indicated otherwise by
computing may be supported , at least in part, by virtualiza context. Therefore , herein , “ A and B ” means “ A and B ,
tion software . A cloud computing environment may be jointly or severally," unless expressly indicated otherwise or
established by an enterprise and/ or may be hired on an indicated otherwise by context.
as-needed basis from a third party provider. Some cloud This disclosure encompasses all changes , substitutions,
computing environments may comprise cloud computing 30 variations , alterations, and modifications to the example
resources owned and operated by the enterprise as well as embodiments herein that a person having ordinary skill in
cloud computing resources hired and /or leased from a third the art would comprehend . Similarly, where appropriate, the
party provider. appended claims encompass all changes , substitutions ,
In some embodiments, some or all of the functionality variations, alterations, and modifications to the example
disclosed above may be provided as a computer program 35 embodiments herein that a person having ordinary skill in
product. The computer program product may comprise one the art would comprehend . Moreover, reference in the
or more computer readable storage medium having com - appended claims to an apparatus or system or a component
puter usable program code embodied therein to implement of an apparatus or system being adapted to , arranged to ,
the functionality disclosed above. The computer program capable of, configured to , enabled to , operable to , or opera
product may comprise data structures, executable instruc - 40 tive to perform a particular function encompasses that
tions, and other computer usable program code . The com - apparatus, system , component, whether or not it or that
puter program product may be embodied in removable particular function is activated , turned on , or unlocked , as
computer storage media and / or non -removable computer long as that apparatus, system , or component is so adapted ,
storage media . The removable computer readable storage arranged , capable , configured , enabled , operable , or opera
medium may comprise , without limitation , a paper tape, a 45 tive .
magnetic tape , magnetic disk , an optical disk , a solid state Any of the steps , operations, or processes described
memory chip , for example analog magnetic tape , compact herein may be performed or implemented with one or more
disk read only memory (CD -ROM ) disks, floppy disks, jump hardware or software modules , alone or in combination with
drives , digital cards, multimedia cards, and others . The other devices . In one embodiment, a software module is
computer program product may be suitable for loading , by 50 implemented with a computer program product comprising
the computing system 30 , at least portions of the contents of a computer -readable medium containing computer program
the computer program product to the secondary storage 984 , code, which can be executed by a computer processor for
to the ROM 986 , to the RAM 988 , and/ or to other non - performing any or all of the steps , operations , or processes
volatile memory and volatile memory of the computing described .
system 30 . The processor 982 may process the executable 55 Embodiments of the invention may also relate to an
instructions and/ or data structures in part by directly access - apparatus for performing the operations herein . This appa
ing the computer program product, for example by reading ratusmay be specially constructed for the required purposes,
from a CD -ROM disk inserted into a disk drive peripheral of and /or it may comprise a general-purpose computing device
the computing system 30 . Alternatively , the processor 982 selectively activated or reconfigured by a computer program
may process the executable instructions and/ or data struc - 60 stored in the computer . Such a computer program may be
tures by remotely accessing the computer program product, stored in a tangible computer readable storage medium or
for example by downloading the executable instructions any type ofmedia suitable for storing electronic instructions,
and /or data structures from a remote server through the and coupled to a computer system bus . Furthermore, any
network connectivity devices 992. The computer program computing systems referred to in the specification may
product may comprise instructions that promote the loading 65 include a single processor or may be architectures employ
and /or copying of data , data structures , files, and /or execut- ing multiple processor designs for increased computing
able instructions to the secondary storage 984 , to the ROM capability.
 US 9, 759,838 B2
49 50
Although the present invention has been described with 10 . The method of claim 1, wherein the second source
several embodiments, a myriad of changes, variations, comprises a measurement of a horizontal electromagnetic
alterations , transformations, and modifications may be sug - field at the surface of the earth , the horizontal electromag
gested to one skilled in the art, and it is intended that the netic field responsive to the subsurface earth formation .
present invention encompass such changes, variations, 5 11. The method of claim 1 , wherein the second survey
alterations , transformations, and modifications as fall within data is obtained by a second plurality of sensors configured
the scope of the appended claims. Moreover, while the to be arranged in a pattern and operable to detect a horizontal
present disclosure has been described with respect to various electromagnetic field at the surface of the earth , the hori
embodiments , it is fully expected that the teachings of the zontal electromagnetic field responsive to the subsurface
present disclosure may be combined in a single embodiment 10 earth formation .
as appropriate . 12 . The method of claim 1 , wherein the second available
What is claimed is : source comprises a passive measurement of spontaneous
1 . A method for surveying, comprising: potential generated between a ground sensor and a wellbore
receiving , by a processor, first survey data from a first at least one depth .
source , the first source comprising a first signal gener- 15 13. A system comprising :
ated by a subsurface earth formation in response to a a plurality of sensors operable to detect first survey data
passive -source electromagnetic signal, wherein the by detecting a first signal generated by a subsurface
electromagnetic signal is generated by an electroseis earth formation in response to a passive - source elec
mic or seismoelectric conversion of the passive-source tromagnetic signal, wherein the electromagnetic signal
electromagnetic signal; 20 is generated by an electroseismic or seismoelectric
receiving, by the processor, second survey data from a conversion of the passive -source electromagnetic sig
second source ; nal;
processing the first survey data and the second survey data a processor operable to :
to determine one or more properties of a subsurface receive first survey data from at least one of the plurality of
earth formation ; 25 sensors;
generating a model of the subsurface earth formation receive second survey data from a second source;
based , at least in part, on the one ormore properties of process the first survey data and the second survey data to
a subsurface earth formation ; and determine one or more properties of a subsurface earth
wherein the passive - source electromagnetic signal formation ; and
includes the earth 's natural electromagnetic field and 30 generate a model of the subsurface earth formation based ,
wherein the processing the first survey data and the at least in part , on the one or more properties of a
second survey data to determine the one or more subsurface earth formation
properties of the subsurface formation is based , at least wherein the passive-source electromagnetic signal
in part, on a correlation of the earth 's electromagnetic includes the earth ’s natural electromagnetic field and
field and the electromagnetic signal generated by the 35 further wherein processing the first survey data and the
electroseismic or seismoelectric conversion of the second survey data to determine the one or more
earth 's natural electromagnetic field . properties of the subsurface earth formation is based , at
2 . The method of claim 1 , wherein the model of the least in part, on a correlation of the earth 's electromag
subsurface earth formation is a three - dimensionalmodel. netic field and the electromagnetic signal generated by
3 . The method of claim 1 , wherein the model of the 40 the electroseismic or seismoelectric conversion of the
subsurface earth formation is a four -dimensional model. earth 's natural electromagnetic field .
4 . The method of claim 3, wherein the four -dimensional 14 . The system of claim 13, wherein the processor is
model is a time-based model. further operable to :
5 . The method of claim 1 , further comprising : update the model of the subsurface earth formation based ,
updating the model of the subsurface earth formation 45 at least in part, on the one or more properties of a
based , at least in part , on the one or more properties of subsurface earth formation .
a subsurface earth formation . 15 . The system of claim 13, further comprising a lock - in
6 . The method of claim 1, wherein the first signal com - amplifier to isolate the electromagnetic signal.
prises a vertical component of an electromagnetic signal or 16 . A system comprising:
a seismic signal. 50 a plurality of sensors operable to detect first survey data
7. The method of claim 1 , wherein processing the first by detecting a first signal generated by a subsurface
survey data comprises : earth formation in response to a passive - source elec
applying at least one time - domain filter or at least one tromagnetic signal, wherein the electromagnetic signal
frequency -domain filter to the first survey data to obtain is generated by an electroseismic or seismoelectric
filtered first survey data ; and 55 conversion of the passive - source electromagnetic sig
identifying a signal of interest from the filtered first nal;
survey data , the signal of interest indicating the one or a lock - in amplifier to isolate the electromagnetic signal;
more properties of the subsurface earth formation . a processor operable to :
8 . The method of claim 1 , wherein the second source receive first survey data from at least one of the
comprises a second signal generated by a subsurface earth 60 plurality of sensors ;
formation in response to a controlled source electromagnetic receive second survey data from a second source ;
signal, the controlled source electromagnetic signal gener process the first survey data , the second survey data , and
ated by a power source configured to drive an electric the isolated electromagnetic signal to determine one or
current into the earth . more properties of a subsurface earth formation ; and
9 . The method of claim 1, wherein the second source 65 generate a model of the subsurface earth formation based,
comprises a second signal generated by a subsurface earth at least in part, on the one or more properties of a
formation in response to an active source of seismic energy. subsurface earth formation
 US 9 ,759,838 B2
51 52
wherein the passive -source electromagnetic signal
includes the earth ' s natural electromagnetic field and
further wherein processing the first survey data and the
second survey data to determine the one or more
properties of the subsurface earth formation is based , at 5
least in part, on a correlation of the earth 's electromag
netic field and the electromagnetic signal generated by
the electroseismic or seismoelectric conversion of the
earth ' s natural electromagnetic field .
17 . The system of claim 16 , wherein the processor is 10
further operable to :
update the model of the subsurface earth formation based ,
at least in part , on the one or more properties of a
subsurface earth formation .
18 . The system of claim 16 , wherein the model of the 15
subsurface earth formation is a three - dimensionalmodel.
19 . The system of claim 16 , wherein the model of the
subsurface earth formation is a four - dimensional model.
20 . The system of claim 19 , wherein the four - dimensional
model is a time-based model. 20
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