GeoVista Sonic Sonde Description

Introduction

The GeoVista sonic sonde is a modular sonde capable of recording full wave
acquisitions from two receivers simultaneously. Delta T measurements are also made
allowing a borehole compensated formation velocity curve to be displayed.

A complete sonic sonde comprises seven components, these being;

Transmitters * 2, TX1 and TX2

Receivers * 2, RX1 and RX2
Acoustic isolation sections * 3

In the event that a Cement Bond Log (CBL) sonde has been purchased, then TX2
will be absent and there will only two acoustic isolation sections.

A description of the modules that are used to assemble a sonde are shown below,
these units being receivers, transmitters and acoustic isolation sections.

Specifications.

Sonde diameter 60 mm

Receiver Length 280 mm

Transmitter length 380 mm

Isolator Length Typically 490 mm or 640 mm

Acoustic transducers 50 mm diameter * 38 mm high * 5 mm wall thickness

Resonant frequency 20 kHz

Transmitter energy 45 milli Joules per firing

Amplifier 16 levels of gain, automatic or manual control

ADC 12 bits conversion

Acquisition period 2 milli seconds

Sample period 4 micro seconds

Bayonet Sonic Sonde Receiver Module.
Connection
The receiver section as shown contains the acoustic
transducer and the complete electronics to support
acoustic data acquisition and telemetry of the data to
surface.

Each end of the unit has a 7 way Cannon connector,

RX and both ends are the same. A bayonet fitting is
Crystal included to ensure correct orientation when connecting
with the acoustic isolation sections.

‘O’ ring seals are provided which engage with the bore
of the isolation sections when assembled.

Usually two receivers are used to assemble a sonde,

and they are engraved as either RX1 or RX2. The only
difference between the RX1 and RX2 units is their
telemetry address.
Electronics
section Usually a complete sonde will have a combination of
transmitters and receivers with the same serial number,
although they could be interchanged if required.

Bayonet
Connection
 Sonde head
Sonic Sonde Transmitter Module.
connection
The transmitter module is as shown.
Again, a complete sonic sonde will have
two transmitters, TX1 and TX2.

TX Crystal There are some differences between these

units. TX1 is designed to go at the top of
the sonde, and as such has a female
connector at the top as shown. A TX2
module is designed to go on the bottom of
the sonde and has a male thread for
Electronics connection to sondes below.
Section
Both of these couplings are the same as
other GeoVista stackable sondes.

The identity of the unit is engraved onto

the body.

Both TX1 and TX2 modules have the same

bayonet fitting for connection to the
acoustic isolation units.
Locking ring

Bayonet
connection
 Upper
Coupling Acoustic Isolation Section.

Two or three acoustic isolation sections are

provided with the sonde (two for a CBL, 3
for a full sonic).

All isolation sections are identical other than

for their length. Due to the different
spacings adopted by the industry, different
Acoustic
isolator sections are available to suit the
isolation application.
Section
Each end of the isolation section has a 7 way
cannon connector and a socket arrangement
to accommodate the bayonet connection of
the acoustic transducers.

Lower
Coupling
 Full Sonic Sonde Assembly

Caution
When assembling the sonde, ensure that all couplings are tight but
Under No Circumstances
apply any torque to the transmitter or receiver crystal housings

For this assembly, two receivers, RX1 and RX2, two transmitters, TX1 and TX2,
and three acoustic isolation sections are required.

When assembled, the sequence form the uphole end of the sonde downwards will be;

TX1, acoustic isolator, RX1, acoustic isolator, RX2, acoustic isolator, TX2

With a set of isolators set for 3’ and 5’ spacings, then the short isolator will be in the
centre of the sonde. The other two isolators will be of equal length.

Note that the receivers will be assembled as the mirror image of each other, with the
end of the receiver containing the receiver crystal towards the centre of the sonde.
Similarly, the transmitters will be assembled as mirror images, but there is no option
for error here as the couplings do not permit incorrect assembly. As a final check,
after assembly measure the spacings between the crystal housings on the transducers
to ensure all is well.

To complete the assembly, observe that there are three screws at each bayonet
coupling. Also each bayonet coupling has a locking ring as identified on the
transmitter drawing above. A receiver has two such rings. These should be screwed
fully onto the bayonet thread before assembly by hand pressure alone.

Observe that the ‘O’ rings are in good condition and apply a small amount of silicon
grease if required.

Push home the bayonet connections, aligning the bayonets with the cutouts in the
acoustic isolators before doing so. If there is any undue resistance, check that there is
no debris or other problem. A large force is not required.

When safely pushed home, observe that the three holes in the isolator section align
with the threaded holes in the transducer bayonet. Apply a small amount of copper
slip grease to the screws and screw in the three screws securely.

Observe that when correctly assembled, the sections are retained by the head of the
screw, not the threaded portion. This is much stronger and more secure. Ensure that
all three screws are correctly seated.

The final stage of the bayonet assembly is positioning the locking ring. The type of
connection used is not very rigid, which is undesirable. The locking ring can be
tightened against the end of the acoustic isolator to pull the connection rigid.
Excessive torque is not required here, just hand tight then gentle pressure with the ‘C’
spanner.

Complete the assembly of all the bayonet connections in the same manner.

Disassembly is the reverse of assembly, with the feature that the locking ring can be
used to “jack out” the bayonet if required.

If a CBL sonde is being assembled, then the method is the same except that the
module layout will be;

TX1, acoustic isolator, RX1, acoustic isolator, RX2, Lower adapter.

The lower adapter has not been shown, but attaches to the lower bayonet of the RX2
module and provides a male sonde thread connection at the bottom of the CBL sonde.

The white plastic sections should not be removed. They may turn with hand pressure.
This is not a problem, they do not form part of the strength of the sonic sonde.

Other sondes, such as centralisers or natural gamma sondes may be stacked with the
sonic sonde as usual with GeoVista equipment.

Module wiring

The sonic wiring diagram is attached to the end of this document.

It can be seen that only four of the Cannon seven connections are used. This allows
some scope for field repair if a pin becomes damaged.

Document Revision.

Revision A
Sonic Sonde Software operations

This manual describes the operation of the software to run the GeoVista sonic sonde.
Operation of the sonde as a fullwave compensated sonic sonde (FWSS) and as a cement
Bond Log (CBL)

It is assumed that the user is familiar with general operations of the GeoVista platform logger
and is familiar with the assembly of the sonic sonde as described in the manual available on
request from GeoVista. Some familiarity with user functions is also required. A manual
describing these is also available from GeoVista. Normally, all required manuals will be on
the accompanying CD distributed with the system.

The user should ensure that the version of software is version 5.2 or later. Advice on the
suitability of the users software is available from GeoVista. Only USB enabled systems
support the sonic sondes.

Building the Stack.

As described in the sonic sonde hardware manual, the sonde is composed of RX1, RX2,
TX1 and TX2 modules, with the appropriate acoustic isolation modules. Different
configurations give the FWSS stack and the CBL stack.

Firstly, some points regarding the naming of the modules when building a stack. For a CBL
stack we name the modules

TX1A, RX1A, RX2A.

For a FWSS stack, we name the units

TX1B, RX1B, TX2B, RX2B.

There are two things to note here.

Firstly, in the CBL stack, we use module names with the suffix A and the suffix B when
building a FWSS stack. The physical units RX1A and RX1B are the same piece of
equipment but they are treated differently in the software. Basically, the modules have two
alternative descriptions. It is important that the correct unit name is specified or the depth
offsets applied will be wrong.

Secondly, we declare the sequence of the modules in the FWSS sonde in an order differently
from that in which we physically build the stack. The reason for this is to ensure that the
transmitters click in the correct timing sequence. If the stack is specified in the software as it
is physically assembled, then the tail end of the acoustic wiggle generated from the TX2B
firing will encroach on the start of the wiggle obtained from the TX1B click and a poor log
will result.
So, to summarize these points:

1 Use module names with a suffix A for the CBL sonde

2 Use module names with a suffix B for the FWSS sonde
3 Build the CBL stack and define the CBL stack in the software in the same way i.e.
TX1A,RX1A,RX2A.
4 Build the FWSS stack as TX1B,RX1B,RX2B,TX2B but define it in the software as
TX1B,RX1B,TX2B,RX2B.

Testing The Stack In The Diagnostic Screen.

When the required stack has been physically assembled and the stack defined in the GV
Platform logger software, select the stack and enter the diagnostic screen. At this point the
sonde should be in an environment where there is good acoustic coupling between the
receivers and transmitters.

Select the RX1B sonde (or RX1A for CBL stack) and the display should be as below.
Note that the representation of this screen shot in the PDF file is not perfect! Areas of
interest can be zoomed in for a better display. This applies to screen shots further into the
manual.

Firstly, note that we have selected a RX1A module, so this is a CBL stack. The display for
an RX1B is identical other than the module name. Similarly, an identical display would be
obtained if an RX2A or RX2B were selected.

Commands To A Receiver.

Note that there a et of commands that can be sent to the receiver module. These are;

Increase Gain: The receiver amplifier has 16 levels of gain, 0 to 15, and the currently
selected gain is displayed in channel 1 of the sonde data channels. Pressing this command
button will increase the gain by 1.

Decrease gain: Similarly, pressing this command button will decrease the gain by 1.

Neither command button will cause a rollover from 15 to 0 or 0 to 15.

Automatic Gain: Rather than selecting the gain manually, the user may select to have
automatic gain selected. The sonde will then take a measure of the amplitude of the received
signal each reception and adjust the gain accordingly so there is little or no saturation of the
signal. When automatic gain is selected, then channel 4, “AGC”, will have a value of 1,
otherwise a value of zero.

Note that sending either an Increase or Decrease gain command will automatically deselect
automatic gain control.

Increase Discriminator: The transit times are determined by detecting when the received
signal crosses the discriminator threshold. The level of the discriminator is shown as a red
horizontal line in the wiggle display window and it can be adjusted by this command and
Decrease Discriminator command. Note that the discriminator is actually downhole in the
receiver module. The current value of the discriminator is transmitted to surface and
displayed as the red line. The transit time displayed (discussed in the transmitter section) is
actually measured downhole and transmitted to surface.

Wiggle Display Area

The wiggle display area, at the bottom of the screen, shows the signal received at the
receiver transducer. This is digitized to 12 bit resolution and transmitted digitally to the
surface. Also displayed here is the threshold as a red line.

If the cursor is placed in this window, then at the top left hand side of this window, the
transit time at the point on the X axis where the cursor is placed is displayed in microseconds.
This is useful to get an indication of the transit times being measured, but it has poor
resolution as compared to the transit time measured in the sonde. The surface resolution is
dependant on screen resolution, and is typically 4 microseconds, while the downhole transit
time measure circuit has 0.2 microseconds resolution and is more accurate.

CBL Selection

There is a checkbox labeled “CBL Mode” to the right of the wiggle display window. If this
is clicked, then the CBL pipe gate will appear. This is the green coloured box and its
position and width can be adjusted using the slider controls that appear when CBL mode is
selected.

The highest amplitude of the section of the wiggle that appears in this pipe gate will be
measured and displayed in the channel #6, “AMP3” (or AMP5 for an RX2 module), and is
the basis of the CBL amplitude measurement.

Note that different predetermined sizes and positions of the pipe gate can be established and
selected from the drop down box. There are upto 4 preset sizes available, and they are
defined in the \GVSYSTEM\GV_SYS.INI file on the logging computer.

When the pipe gate positions are moved, then the position and width are stored in this file.
The names cannot be edited from here, but the GV_SYS.INI file can be edited using, for
example, Notepad editor.

A sample is shown here where n is 1 to 4. There is only a need to edit the name to suit, as
the times will automatically be updated when changed in the logging screen

[CBL Casing Size n]

Description=9 5/8 Casing
RX1A StartgateTime(usec)=380
RX1A GateWidth(usec)=50
RX2A StartgateTime(usec)=768
RX2A GateWidth(usec)=38

Receiver Channels

Several have been mentioned previously, but a summary is presented here.

Channel #1 GAIN dB

This displays the currently selected amplifier gain applied to the current wiggle acquisition.
Uncalibrated it will display the values 0 to 15, and it can be calibrated into dB if required.

Channel #2 SAMP uSEC

This is the sample rate of the wiggle, and is currently fixed at 4 microseconds.
Channel #3 OFF REC

This is the offset, in terms of downhole ADC samples, at which the digital transmission
starts. Currently this is fixed at zero.

Channel #4, AGC

When displaying 1, then the sonde will apply the automatic gain control (AGC) algorithm
and adjust the gain of the downhole amplifier to avoid saturation of the receiver amplifier.
The gain selected is transmitted and displayed in Channel #1. When AGC is off, a 0 is
displayed and the gain used is as set by the user.

Channel #5, AMP3 MV

This is the maximum amplitude obtained from the wiggle in the region of the user set pipe
gate. Note that this curve is operational in both FWSS and CBL modes, but is not reliable in
FWSS mode.

In CBL mode, this can be calibrated in the normal manner. Note that a test pipe is often
required to calibrate this correctly. Refer to local practice for the calibration method.

Channel #6 FW 3FT

The data for this channel is as displayed in the wiggle display area. The presence here of this
channel holder allows the user to change the scales for this curve.

Transit Time measurements

Apart from the full wave data that can be presented, transit time measurement is also
required. There are 4 transit times that are measured, and these are as shown on the
schematic “Sonic Sonde transit Time Definition”

Transit Time TT_A Time from TX1 to RX1

Transit Time TT_B Time from TX1 to RX2

Transit Time TT_C Time from TX2 to RX2

Transit Time TT_D Time from TX2 to RX1

The units of these measurements are all microseconds, and are a function of the borehole
size, the borehole fluid and the sonde diameter as well as the formation velocity. Clearly,
what is required is the formation acoustic propagation delay.

As the spacing between TX1 and RX1 is the same as the spacing between TX2 and RX2, the
propagation delay of the formation can be calculated as;
Propagation delay = ((TT_B + TT_D) – (T T_A + T T_C))/Spacing microseconds per foot.

The units are microseconds per foot as the spacing is often measured in feet. A common
value for Spacing is 2’.

To calculate this compensated propagation delay in real time requires the user function
facility of the GeoVista platform logger. A sample program to calculate this is attached to
this document.

The component transit times can be observed by displaying the TX1 and TX2 modules from
the sonde stack, as seen on the screen shot below.

The display shows the two transit times associated with TX1, which are TT_A and TT_B.
The transit times TT_C and TT_D are associated with TX2.
Also shown is a gain value. Referring back to the full wave display from RX1 or RX2, there
is the opportunity to both control the gain of the receiver amplifier and also to set the
threshold value that is applied in the sonde. For example, when displaying the full wave
display from RX1, the time that is measured when the first arrival crosses the discriminator
will be measured in the sonde and transmitted as TT_A in TX1 module display.

Similarly, when displaying the full wave display from RX2, the time that is measured when
the first arrival crosses the discriminator will be measured in the sonde and transmitted as
TT_D in TX1 module display.

This is as a consequence of the aspect of the sonde operation where by the wiggle waveforms
are both captured when TX1 is fired. There is no full wave acquisition from TX2 firing, jut
transit time measurements are made from TX2 firing.

To summarize what has been said in the last 3 paragraphs, the use can see the signals from
which TT_A and TT_D are measured from but the wiggles from which TT_C and TT_B are
measured are not available for display. Also, the same discriminator value will be applied to
both TT_A and TT_B measurements as specified in the RX1 display window. Similarly,
the same discriminator value will be applied to both TT_C and TT_D measurements as
specified in the RX2 display window.

The user only has the option of setting the gain independently for the acquisitions where the
full wiggle is not displayed, namely transit times TT_B and TT_C. These rae the gain values
displayed in the TX1 and TX2 module display window.

The criteria for setting the gain is basically to set the maximum value, although consideration
should be given to the possibility of road noise causing early discrimination.
 User Function To Calculate Compensated Propagation Delay

Name Function For GeoVista

Author Martin Payne
Created July 2002
Creates compensated velocity
Definition section

Create PDEL:US\F TK1 TK1 0.00 400.00 Blue 2

Code Section

PUSH RX1B:TT_A;
PUSH RX2B:TT_C;
ADD;
PUSH RX1B:TT_B;
PUSH RX2B:TT_D;
ADD;
SUBTRACT;
POP PDEL:US\F;
END;
Representation Of FWSS Sonde

TX1

TA

RX1

TB

Spacing

RX2

TD

TC

TX2

Sonic Sonde transit Time Definition

 1 2 3 4

D D

Transmitter1
Transmitter2 Receiver2 Receiver1
PL1 PL2 PL1 PL2 PL1 PL2
C C
A Red A A Red A A Red A
Sonde Bottom Line Line Line Line Line Line Line Line Line Line Sonde Head
B Black B B Black B B Black B
Gnd Ground Ground Gnd Ground Ground Gnd Ground Ground Gnd
C Pink C C Pink C C Pink C
TX1 Fire TX1 Fire TXSense TX1 Fire TX1 Fire TXFire TX1 Fire TX1 Fire Trigger
D White D D White D D White D
Trigger TX2 Fire TX2 Fire TXFire TX2 Fire TX2 Fire TXSense TX2 Fire TX2 Fire
E E E E E E
NC NC NC NC NC NC
F F F F F F
NC NC NC NC NC NC
G G G G G G
NC NC NC NC NC NC
CANNON_7 CANNON_7 CANNON_7 CANNON_7 CANNON_7 CANNON_7

Use screened wire for the C & D connections through the RX section.
Ground the screens at the electronics end via a tag to chassis.and have a single connection to the boards.

B B

GeoVista - Unit 6, Cae Ffwt Business Park,

Glan Conwy, Conwy, LL28 5SP.
Tel +44 (0)1492 573399 Fax +44 (0)1492 581177

A A
Drawn MP Issue Circuit Description Checked Date Issue Parts List Checked Date Title: Sonic Sonde Wiring
Date Jan 2000 B Added use of screened wires in RX module MP June 2000 PCB Ident: Filename Issue B
NA ISOL_1.SCH
Sheet Of 1 Of 1 Project

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