United States Patent (19) 11 Patent Number: 4,493,369

Odeh et al. Best Available C 45) Date of Patent: Jan. 15, 1985
(54) METHOD OF IMPROVED OIL RECOVERY 4,252,191 2/1981 Pusch et al. ......................... 166/61
BY SIMULTANEOUS INJECTION OF 4,274,487 6/1981 Hollingsworth et al. .......... 66/26
WATER WITH AN IN-STU COMBUSTION FOREIGN PATENT DOCUMENTS
PROCESS
11 12956 5/1968 United Kingdom ................ 66/272
(75) Inventors: Aziz S. Odeh, Dallas; Billy J. Dotson,
Grand Prairie, both of Tex. Primary Examiner-George A. Suchfield
Attorney, Agent, or Firm-Alexander J. McKillop;
(73) Assignee: Mobil Oil Corporation, New York, Michael G. Gilman; Malcolm D. Keen
N.Y.
57 ABSTRACT
21 Appl. No.: 478,596 A method of recovering heavy oil from a subterranean,
22 Filed: Mar. 24, 1983 permeable, heavy oil-bearing reservoir in which an
oxygen-containing gas is injected into the lower portion
Related U.S. Application Data of the reservoir to establish an in-situ combustion reac
63 Continuation of Ser. No. 259,330, Apr. 30, 1981, aban tion therein and to form a combustion front near the
doned. injection well. Injection of the oxygen-containing gas is
continued to advance the combustion front that heats
51 Int. Cl. ............................................ E21B 43/243 the oil and generates gas to displace the oil through the
52) U.S. Cl. ..................................... 166/261; 166/269 reservoir toward a producing well. Water is injected
58) Field of Search ........................ 166/261, 269, 272 into the upper portion of the reservoir during combus
56) References Cited tion to prevent gases from migrating into the upper
U.S. PATENT DOCUMENTS portion of the reservoir, scavenge heat from the burned
out portion of the reservoir, and displace oil from the
2,788,071 4/1957 Pezet .................................. 66/261 reservoir, particularly the lower region, toward a pro
2,994,375 8/1961 Hurley ... ... 166/26 X duction well. The areal sweep efficiency of the injected
3,208,519 9/1965 Moore ................................. 166/26
3,448,807 6/1969 Strickland, Jr. .................... 166/256 water may be improved by the addition of thickening
3,978,920 9/1976 Bandyopadhyay et al. ... 166/261 X agents and water-soluble polymers.
4,042,026 8/1977 Pusch et al. .................... 166/26 X
4, 166,504 9/1979 Brown et al. ....................... 166/272 8 Claims, 1 Drawing Figure

r
- 8
SS -
{&SSS&
U.S. Patent Jan. 15, 1985 4493,369

|
|
8

No.a 2
#7
 4,493,369 2
1
the low density products of combustion tend to segre
METHOD OF IMPROVED OIL RECOVERY BY gate to the top. In addition to very effective contact and
SIMULTANEOUS INJECTION OF WATER WITH heat exchange between the water and the gaseous prod
AN IN-STU COMBUSTION PROCESS ucts of combustion, the water tends to fill gas-swept
5 channels thus impeding the flow of gases and diverting
This is a continuation of copending application Ser. them to previously unswept paths resulting in higher
No. 259,330, filed Apr. 30, 1981, now abandoned. vertical sweep efficiency. The water passing through
the combustion-heated formation scavenges heat and
BACKGROUND OF THE INVENTION becomes a hot water drive displacing oil from lower
1. Field of the Invention O regions, not subjected to combustion, which further
This invention concerns a thermal oil recovery improves recovery efficiency per BTU of heat injected.
method utilizing in-situ combustion and water in a This type of vertical crossflow of fluids within a reser
method which permits efficient recovery of heavy oil voir enables the reservoir to be more efficiently heated
from permeable, heavy oil-bearing reservoirs. over the areal extent of the reservoir thereby greatly
2. Background and Prior Art 15 enhancing the recovery of oil. Mobility control agents
It has been proposed to recover oil, in the nature of such as thickeners and water-soluble polymers may be
heavy viscous oils, from a subterranean reservoir by a added to the injected water to improve its areal sweep
method which is commonly known as in-situ combus efficiency.
tion. In this method, an oxygen-containing gas is in BRIEF DESCRIPTION OF THE DRAWING
jected into the reservoir through an injection well with 20
ignition of oil within the adjacent reservoir initiated by The drawing is a view in cross-section of an injection
suitable means for establishing a combustion front. The well and a production well penetrating a subterranean,
reservoir is usually provided with one or more produc permeable, heavy oil-bearing reservoir illustrating the
tion wells for the production of oil. As the flow of invention.
oxygen-containing gas to the reservoir is continued, the 25 DESCRIPTION OF THE PREFERRED
combustion front is moved from the injection well EMBODIMENTS
toward the production wells. The heat generated by
burning reduces the viscosity of the oil which is dis Thus, according to the drawing, a subterranean, per
placed before the combustion front toward the produc meable, heavy oil-bearing reservoir 10, is overlain by
tion wells from which the oil is recovered. The combus 30 overburden 12 and underlain by basement formation 14.
tion front in displacing the mobile oil before it in the The reservoir 10 is penetrated by an injection well 16
reservoir uses the residual carbonaceous deposit as fuel. and a production well 18.
In these processes, the gaseous combustion products The injection well 16 has perforations 20 providing
and light hydrocarbons are considerably lighter than fluid communication into the upper portion of reservoir
the oil and water present in the reservoir and thus, 35 10 and perforations 22 providing fluid communication
because of gravity segregation, tend to rise to the top of into the lower portion of the reservoir. A tubing string
the reservoir when vertical communication exists. Con 24 extends from the earth's surface to the lower portion
sequently, these products channel through the top of of reservoir 10 forming an annulus 26 between the tub
the formation to the producing well overriding a major ing string and injection well casing 28.
portion of the reservoir and contacting only a small 40 A packer 30 seals the outer tubing surface from the
fraction of the reservoir oil. This behavior results in inside of casing 28. The top of injection well 16 is pro
inefficient oil recovery and low vertical sweep effi vided with a means 31 for injecting fluid into the annu
clency. lar space 26 between tubing 24 and casing 28.
Furthermore, in such in-situ combustion processes, The production well 18 has perforations 32 providing
large quantities of heated rock are left behind in the 45 fluid communication into the lower portion of reservoir
reservoir. This heat is therefore lost, which greatly 10 for the production of oil and gases through conduit
reduces the thermal efficiency of the process. 34 to the surface of the earth.
Our improved invention provides a substantial ad According to one presently preferred mode of opera
vance in recovering heavy oil from permeable, heavy tion, the lower portion of the oil-bearing reservoir 10 is
oil-bearing reservoirs utilizing in-situ combustion. 50 ignited in the vicinity of perforations 22. After ignition,
SUMMARY OF THE INVENTION
an oxygen-containing gas such as oxygen or air or mix
tures thereof is injected through tubing string 24 into
According to the present invention, we have found the lower portion of the reservoir through perforations
an improved method for recovering oil, especially vis 22. A combustion front is formed which progressively
cous or heavy oil, from a permeable, heavy oil-bearing 55 advances from the injection well to the production well.
reservoir wherein in-situ combustion is established in After the combustion front has advanced a sufficient
the lower portion of the reservoir, water is injected into distance, water is injected through injection means 31
the upper portion of the formation at controlled rates into the annulus 26 formed between casing 28 and tub
and oil is recovered at a production well. An oxidizing ing 24 and outwardly through perforations 20 and into
gas such as air or oxygen or mixtures thereof is injected 60 the upper portion of the reservoir 10.
into the lower portion of the reservoir to form a com The water, with a higher density, tends to segregate
bustion front which advances through the reservoir to the bottom of the formation because of gravitational
toward a production well. Heat generated by the in-situ forces, whereas the low density combustion gases tend
combustion reaction heats the viscous oil as it advances to segregate to the top. The water tends to fill gas-swept
through the reservoir thereby reducing its viscosity. 65 channels thus impeding the flow of gas and diverting
The water injected above the in-situ combustion front, them to previously unswept paths resulting in higher
with a higher density, tends to segregate to the bottom vertical sweep efficiency. The water passing through
of the reservoir because of gravitational forces, whereas the combustion-heated reservoir scavenges heat and
 4,493,369 4.
3
becomes a hot water drive displacing oil from lower line parallel to a line intersecting the plurality of injec
regions of the reservoir, not subjected to combustion, tion wells. In addition, a circular drive pattern may be
which further improves recovery efficiency. used in which the injection system comprises a central
The combustion front and water advance through the injection well and the production system comprises a
reservor 10 contacting the oil and reducing its viscosity 5 plurality of production wells about the injection well in
and displacing the oil towards production well 18. Ad a ring pattern such as a 5-spot or 7-spot well pattern.
mixtures of oil and gases enter production well 18 We claim:
through the lower perforations 32, pass up through 1. A method for recovering heavy oil from a subterra
conduit 34 and are recovered at the surface of the earth. nean, permeable, heavy oil-bearing reservoir penetrated
Once the combustion front is sufficiently near to the 10 by an injection well and a production well, comprising:
production well which can be ascertained by a rise in (a) establishing a burning zone in the lower portion of
the temperature at the production well, further injec said reservoir at the face of said injection well;
tion of the oxidizing gas is discontinued. Water injection (b) injecting an oxygen-containing gas into the lower
may be continued until water breaks through at the portion of said reservoir via said injection well to
production well 18. 5 move said burning zone toward said producing
Water may be injected with the oxygen-containing well and to generate hot combustion gases;
combustion supporting gas after the initiation of in-situ (c) injecting a sufficient amount of water via an injec
combustion so as to absorb heat from the combustion tion well into the upper portion of said reservoir to
zone, which is a technique known in the art as wet impede the flow of said hot combustion gases
combustion. The amount of water injected, in relation 20 through the upper portion of the reservoir, to scav
to the oxygen-containing combustion supporting gas, enge heat from the burned out portion of the for
will vary depending upon the amount necessary to keep mation, and to displace the oil through said reser
the reservoir below excessive temperature levels. It voir towards the lower end of said production well;
must not be so great, of course, as to extinguish combus and
tion as would be evidenced by the composition of the 25
(d) recovering fluids including oil solely from the
gases produced from the reservoir. lower portion of said reservoir via said production
The oxygen-containing gas used to support combus well.
tion can be air, substantially pure oxygen, or oxygen 2. A method for recovering heavy oil from a subterra
enriched air.
The amount of water injected into the upper portion 30 by an permeable,
nean, heavy oil-bearing reservoir penetrated
injection well and a production well, comprising:
of the reservoir is much larger than that used in conven (a) establishing a burning zone in the lower portion of
tional wet combustion processes in order to scavenge said reservoir at the face of said injection well;
sufficient heat from the burned out portion of the reser (b) injecting an oxygen-containing gas into the lower
voir and also to restrict gas flow in the burned zone. portion of said reservoir via said injection well to
However, the injection rate must be controlled or inter 35 move said burning zone toward said producing
mittently discontinued to prevent the water from overr well and to generate hot combustion gases that
riding the combustion front or extinguishing it. reduce the viscosity of the oil and displace the oil
In another embodiment of the invention, separate through said reservoir toward said production
injection wells may be used for the injection of the
oxidizing gas such as air or oxygen and water into the 40 (c)well; injecting a sufficient amount of water via an injec
selected portions of the reservoir. For example, two or tion well into the upper portion of said reservoir to
more closely spaced injection wells may be used with impede the flow of said hot combustion gases
air or oxygen injected near the bottom of the reservoir through the upper portion of the reservoir, to mix
through one well and water injected near the top of all, with the uprising hot combustion gases so as to
or selected, separate wells as dictated by preferred engi 45
scavenge heat therefrom without extinguishing the
neering practices.
In another embodiment of the process of this inven combustion front thereby producing a hot water
tion, the areal sweep efficiency of the water injected drive for displacing oil from lower regions of the
into the upper portion of the reservoir may be improved reservoir, to scavenge heat from the burned out
by the addition thereto of mobility control agents such 50 portion of the formation, and to displace the oil
as thickeners or water-soluble polymers. These agents through said reservoir towards the lower end of
increase the viscosity of the water which decrease its said production well;
mobility with a resulting increase in displacement effi (d) continuing injecting water and oxygen-containing
ciency. Examples of useful thickeners and water-soluble gas into the injection well and producing fluids
polymers useful in connection with this process are 55 solely from the lower portion of said reservoir
disclosed in U.S. Pat. No. 3,500,918 to Holm and U.S. through said production well until the burning
Pat. No. 3,710,861 to Steeg, the disclosures of which are zone of the in-situ combustion operation is near the
hereby incorporated by reference. production well;
The present invention may be carried out utilizing (e) thereafter discontinuing injecting the oxygen-con
any suitable injection and production system. The injec taining gas into the injection well to discontinue
tion and production systems may comprise one or more in-situ combustion and continuing injecting water
wells extending from the surface of the earth into the into the upper portion of the formation via the
oil-bearing formation. Such injection and production injection well; and
wells may be located and spaced from one another in (f) continuing to produce fluids from the lower por
any desired pattern. For example, a line drive pattern 65 tion of the reservoir via the production well until
may be utilized in which a plurality of injection wells breakthrough of the water at the production well.
are arranged in a more or less straight line toward a 3. The method as defined in claim 2 wherein said
plurality of production wells in a more or less straight oxygen-containing gas is air.
 4,493,369 6
5
increased in viscosity by the addition of a thickening
4. The method as defined in claim 2 wherein said agent.
oxygen-containing gas is oxygen-enriched air. 7. The method as defined in claim 2 wherein said
water injected into the upper portion of the reservoir is
5. The method as defined in claim 2 wherein said 5 increased in viscosity by the addition of a water-soluble
oxygen-containing gas is substantially pure oxygen. polymer.
8. The method as defined in claim 2 wherein the
6. The method as defined in claim 2 wherein said injection of water in kstep: (c):k isaeperiodically terminated.
water injected into the upper portion of the reservoir is
O

15

20

25

30

35

45

50

55

60

65