Echometer Model-M
Digital Dual Channel Fluid Level Instrument

Introduction

This operating manual contains information about the Echometer Model M Fluid Level Instrument including operating procedures, maintenance, shooting problem wells, chart interpretation and technical papers relating to the optimization of producing wells. Please read the first 25 pages and view the example of the strip chart output forms and charts on wells before operating the instrument. Additional technical papers can be accessed from the Echometer Web page, www.echometer.com, these articles offer additional information on the use of acoustic fluid level instruments to optimize production. Please read these papers at your convenience.

Limits of Liability

Echometer Company reserves the right to revise its software and publications with no obligation of Echometer Company to notify any person or any organization of such revision. In no event shall Echometer Company be liable for any loss of profit or any commercial damage, including but not limited to special, consequential, or other damages.

Information in this document is subject to change without notice and does not represent a commitment on the part of Echometer Company. The software described in this document is furnished under a license agreement or nondisclosure agreement. It may be used or copied only in accordance with the terms of the agreement. It is against the law to copy the software or any medium except specifically allowed in the license or non-disclosure agreement.

Copyright Notice

Copyright 1997,1998,1999,2000,2001,2002,2003 Echometer Company. All rights reserved. Federal copyright law protects this manual. No part of this manual may be copied or distributed, transmitted, transcribed, stored in a retrieval system or translated into any human or computer language, in any form or by any means, electronic, mechanical, magnetic, manual, photographic, photocopy, scanning, or otherwise, or disclosed to third parties without the express written permission of Echometer Company.

Trademarks

AWP, TWM, Q-Rod, EchoPUMP, Compact Gas Gun are trademarks of Echometer Company

1 - Safety Considerations

Echometer Schools

Additional Information

2 - Principles of Acoustic Measurements

Recording and Interpretation of Signals

Depth Calculation

3 – General Description – Model M

Instrument Panel

Wellhead Attachments

Remote Fire Gas Gun

High Pressure Gas Guns

Accessories

4 - Operation

General Recording Procedure

Operation of the Model M with the Compact Gas Gun

Operation of the Model M with the Remote Fired Gas Gun

Recommendations for Optimum Performance

Automatic Gain Setting (AGS) Mode Characteristics

Manual Gain Setting (MGS) Mode Characteristics

Collar Channel Automatic Gain Control (AGC)

Liquid Level Channel Gain Control

5 - Interpretation

6 - Problem Wells

7 - Battery and External Power Information

Important Notes and Instructions for Rechargeable Batteries

8 - Testing/Troubleshooting

Amplifiers Check

Filters Check

Microphone Cable check

Microphone Check

9 - Maintenance

Compact Gas Gun Pressure Rating

Compact Gas Gun Disassembly and Assembly Special Precautions

Remote Fire Gas Gun Pressure Rating

Remote Fire Gas Gun Disassembly and Assembly Special Precautions

10 – Calculation of Bottomhole Pressures

11 – APPENDIX

Fig. 1a - Compact Gas Gun Assembly Drawing

Fig. 1b - Remote Fire Gas Gun Assembly Drawing

Fig. 2 - Echometer Panel

Fig. 3 – Initial Header and System Test (Shown ½ Scale)

Fig. 4 – Data Information Form and Time Stamp

Fig. 5 – Upper/Lower Collars Accented

Fig. 6 – Prove Liquid Level

Fig. 7 – Well With Liner

Fig. 8 – Records of Compression/Rarefaction Initial Pulse

Acoustic Responses from Downhole Anomalies

Amplifiers And Filters Test

Microphone Cable Test

Microphone Test

Rate of Fill-up Graph

Use of Rate of Fill-up Information

Carbon Dioxide Cylinder

Carbon Dioxide Information (CO2)

Nitrogen Information (N2)

Fig. 9 – CO2 Cylinder w/ Hose

Fig. 10 –Filler Connector for 7.5 OZ. CO2 Cylinder

1 - Safety Considerations

Read this manual before operating the equipment.

Please observe all safety rules in operating this equipment. The pressure ratings of the Echometer gas gun and all fittings, hoses, etc. should always exceed actual well pressure. Because the casing pressure normally increases during a build-up test, caution should be exercised that the well pressure does not exceed equipment pressure ratings.

Do not use worn or corroded parts. A used or corroded fitting may not withstand original pressure rating.

All safety precautions cannot be given herein. Please refer to all applicable safety manuals, bulletins, etc. relating to pressure, metal characteristics, temperature effects, corrosion, wear, electrical properties, gas properties, etc. before operating this equipment.

The tests should not be undertaken if the operator, the test equipment and the well are not in conditions to operate safely. This equipment should not be used if the operator is tired, ill or under the influence of alcohol, drugs or medication.

Echometer Schools

Echometer Company offers schools on the use and applications of this equipment. You are invited to attend free of charge. A list of the schools, which are taught throughout the United States and Canada, will be sent upon request or can be viewed at http://www.Echometer.com

Additional Information

Please contact Echometer Company to obtain additional information or to clarify any questions that you may have in regard to the use of this instrument. The street and mailing address, phone number, fax number and e-mail address are given on the first page.

2-Principles of Acoustic Measurements

Acoustic liquid level instruments were developed in the 1930's. An acoustic wellhead attachment is connected to an opening in the casing annulus at the surface of a well as shown in Figure 1 in the appendix. The acoustic wellhead attachment consists of an acoustic pulse generator, a microphone and optionally a pressure gage. Throughout the years, acoustic pulse generators have included a dynamite cap, 45-caliber blank, 10 gauge black powder blank, a compression gas pulse and a rarefaction gas pulse. The explosive dynamite caps and blanks are a safety hazard and have resulted in damage to wells and environment. While these explosive sources should not create a problem if the casing annulus contains only hydrocarbon gas, major explosions have occurred when oxygen was allowed to enter the casing annulus during work-overs or when special conditions resulted in a vacuum in the casing annulus

The versatility, economy and convenience of gas guns have resulted in widespread use of this type of acoustic pulse generator. The expansion of gas from a volume chamber into the well generates the acoustic pulse. In most cases, compressed CO₂ or N₂ gas is loaded into the volume chamber, which is charged to a pressure greater than the well pressure. A valve in the wellhead attachment is opened rapidly, either manually or electrically, resulting in a pressure pulse being generated in the casing annulus gas. The acoustic pulse travels through the gas in the casing annulus and is partially reflected by changes in cross sectional area such as tubing collars, tubing anchors, casing perforations, etc. The remaining pulse energy is then reflected by the gas/liquid interface at the depth of the liquid level. The reflected signals travel back to the surface of the well where they are detected by the microphone.

The microphone within the wellhead attachment converts the reflected acoustic signal into an electrical signal consisting of a series of pulses, which correspond to the sequence of reflections. The microphone must operate over a wide pressure range from a vacuum to the maximum pressure that exists in the wells being tested. The microphone should be designed to cancel the mechanical vibrations of the wellhead while remaining sensitive to the acoustic signal reflections.

Recording and Interpretation of Signals

An amplifier/recorder filters and amplifies the electrical signal from the microphone and records the enhanced signals on a strip chart. Modern instruments use analog to digital converters and microprocessors to improve the signal quality and print the chart. The frequency content of the reflected acoustic signals varies depending on the characteristics of the initial pulse, the pressure in the gas, the distance traveled and the type of cross sectional area change. In general, as the pulse travels in a gas, the amplitude of the signal decays. The high frequency energy decays more rapidly than the low frequency energy. Thus, the acoustic response from the collars at the top of the well contains high frequency energy, the response from deep collars contains medium frequency and the signal from the liquid level is mostly low frequency energy. This is especially apparent in deep wells with low casing pressure. Fluid level instruments are designed to include various filters, which can be used to accent signals that correspond to these frequency ranges. The Model M records the signal on the dual channels. One channel is tuned to higher frequencies from the collars while the second channel is tuned to low frequencies from the liquid level. Single channel instruments can be operated in any of these modes and it is possible to switch from one frequency response to another while the instrument is recording. Initially, the single channel instrument is operated in the collar mode (high or medium frequency), which is then switched to the liquid level mode (low frequency) when the collar signal fades. Switching may be manual or automatic.

Depth Calculation

In most cases, once a strip chart record has been obtained and the liquid level signal has been identified, the operator must count the number of tubing collar reflections from the surface to the liquid level in order to calculate its depth. The corresponding number of tubing joints, multiplied by the average joint length yields the distance to the liquid level.

Other techniques are available for determining the liquid level depth. When other signals are identified on the chart, such as those generated by gas lift mandrels, liner tops, tubing anchors or perforations, the known depth of these anomalies can be used to calculate the depth to the deeper liquid level by the ratio of chart distance or elapsed time. When the lengths of tubing joints vary considerably, so that an average joint length is not representative, some operators placed an over-sized tubing collar (marker) to serve as a depth reference.

When the specific gravity or the composition of the gas in the annulus is known with some accuracy, then the velocity of sound in the gas can be calculated. The acoustic wave round-trip travel time from the initial pulse to the liquid level reflection is read directly from the strip chart, which displays timing marks. The round-trip travel time is divided by two and multiplied by the acoustic velocity to calculate the depth to the liquid level.

Still another technique involves measuring the acoustic velocity of the gas by sampling the casing gun into a tube of sufficient length to measure the velocity of sound in the gas by pulse testing. This technique is applicable only if the well continuously vents gas from the annulus so that a representative sample of the gas sample obtained at the top of the well will not be representative of the gas in the well.

The most common application of an acoustic liquid level instrument is to measure the distance to the liquid level in the casing annulus of a well. However, it can also be applied to measurements inside tubing. Other applications include determination of the distance to the mud or kill liquid level during drilling and work-overs. The acoustic instruments can be used to measure the distance to any change in cross-sectional area inside pipe or in the annulus.

3 – General Description – Model M

The Echometer Model M is a dual channel, microprocessor controlled amplifier/recorder. It permits better interpretation of reflections from downhole anomalies since two different filters are used to improve the signal. Processing and simultaneously recording reflected signal using two separate amplifiers having different frequency response, improve the ability of the operator to distinguish downhole obstructions from enlargements. The response from the liquid level (orreduction in annulus area) is opposite to the response from an enlargement such as a hole in the casing. The Model M uses modern electronics, integrated circuits, chart drive system and a thermal printhead, which result in a very compact and lightweight system.

The dual channel Model M accents and records collars on one channel, and the liquid level response on a second channel. The collar channel can be set to record sharp upper collars or deep collars. Selecting the proper collar filter will result in more accurate determination of the number of tubing collar reflections from the surface to the liquid level. The lower trace accents the signals from the liquid level, tubing anchor, gas-lift mandrels, casing perforations and other major anomalies.

A microprocessor is used with an analog to digital converter, memory chip, amplifiers, clock, timing circuit and other electronic components to improve the performance and utility of the instrument. When an acoustic pulse is generated in the well, the signals reflected from the collars at the top of the well are large but rapidly attenuate. The microprocessor is programmed to evaluate the signal level and increase or decrease the collar amplifier gain as necessary to optimize the quality of the recording. The collar and other signals will be recorded at a width of approximately 0.6-inch (12-mm), which simplifies the manual counting of the collars since the amplitude of the collar signal is maintained automatically. The automatic control of the recording level is called automatic gain control.

The microprocessor is used in conjunction with a timer. Since these instruments are used throughout the world, the universal coordinated time and date are printed on the strip chart. Also, the timing capabilities of the microprocessor, clock and timing circuit are used to place labeled markers at one-second intervals beginning from the instant the acoustic pulse is generated. This allows the operator to determine the round trip travel time very accurately. The travel time and the distance to the liquid level are used to compute the acoustic velocity of the gas in the annulus. The acoustic velocity the casing pressure and average temperature can be input to the utility program AWP for Windows to compute the gas gravity and the pressure distribution in the well, including the pump intake pressure and the pressure at the perforations.

In addition to recording both collar and liquid level signals simultaneously, the digital printhead generates a header, an analysis form, and prints the values of background noise, battery voltage and special instructions on the strip chart.

The entire instrument is contained in a waterproof, dustproof plastic housing having dimensions of 11 by 10 by 5 inches and weighs 11 pounds (5 kg). The following section describes the instrument panel and the function of the various controls.

Instrument Panel

The instrument panel is shown schematically in Figure 2 in the appendix. The following controls are used for operating the instrument and for checking that it is operating correctly:

Power Switch:

Momentarily placing the switch in the ON position energizes the amplifier, activates a red light that indicates that the battery is powering the electronics and records a header on the strip chart. The microprocessor performs a system test and checks the battery voltage. If the battery voltage is low, a message is printed to charge the battery. If the system is OK, the chart drive stops after printing the battery voltage and test signals on the collar and liquid level channels, and the message " TURN ON CHART DRIVE TO TEST WELL". The power can be turned off manually, or the power will automatically turn off after approximately 15 minutes of non-use.

Upper Collars/Lower Collars Switch:

This two-position switch selects whether the collar channel is connected to the high frequency (Upper Collars) or medium frequency (Lower Collars) filter circuits.

Collars Gain

This knob controls the gain of the collar channel. The most counter-clockwise position (AUTO) activates automatic gain setting and should be used first always. In the AUTO mode, the gain is set automatically. Having the gain indicator on a value greater than 1 when the chart drive is turned on allows the operator to control the amplifier gain by setting the gain control knob as desired before the “shot” is detected. After the “shot” is detected, the instrument uses the gain setting when the shot is detected and the operator cannot adjust the gain.

Liquid Level Gain

This knob controls the gain of the liquid level channel. The most counter-clockwise position (AUTO) activates automatic gain setting and should be used first always. In the AUTO mode, the gain is set automatically. Having the gain indicator on a value greater than 1 when the chart drive is turned on allows the operator to control the amplifier gain by setting the gain control knob as desired before the “shot” is detected. After the “shot” is detected, the instrument uses the gain setting when the shot is detected and the operator cannot adjust the knob.

Chart Drive Switch

This switch is used to turn on and off the chart drive. Turning the switch to ON begins the data acquisition sequence. This consists of printing the data forms followed by the gain settings and the noise level on both channels, followed by the statement GENERATE PULSE and the recording of the two channels. The chart drive continues on until the switch is turned OFF.

Input Connector

This BNC INPUT connector is the input to the amplifiers. When acquiring data, this INPUT connector must be connected to the microphone connector on the acoustic wellhead using a good coaxial cable with clean connectors.

Remote Fire Connector

Connects the instrument to the solenoid valve of a remote fire gas gun if a remote fire gun is utilized.

Remote Fire Switch

Depressing this switch operates the solenoid valve on a remote fired gas gun by applying 12 volts to the solenoid coil. Depress the switch for 1 second to fully release gas from the chamber.

Battery Charger Connector

Attaching the 110 VAC or the 220 VAC battery charger or the 12V-car battery power cable to this connector charges the built-in battery.

Test Connector and Test Switch

This TEST connector should be attached to the INPUT connector using the coaxial cable in order to check that the instrument and the coaxial cable are operating correctly. Depressing the test switch applies a test signal to the input of the amplifier via the TEST connector and the coaxial cable.

· Chart Paper Drive

Pushing the spring-loaded aluminum plate cover towards the right and lifting it from the left side accesses the chart paper. The paper is dropped into the cavity so that it unrolls counter-clockwise. After inserting the paper roll, the aluminum cover is replaced. The printed Echometer logo on the paper should face up since only this side of the paper is heat sensitive. The heat sensitive paper supplied by Echometer Company operates over a wide temperature range and is made for the Echometer Chart drive system. The chart drive has a paper sensor to determine when paper exists in the drive. If the sensor detects that paper is not present, power is not supplied to the printhead. If paper is not present in the drive system and power is supplied to the printhead, the printhead will be damaged because the small heating elements in the printhead will be overheated. Using paper that is not of the proper width may result in printhead failure. Use only Echometer paper to insure proper operation of the printhead and chart drive system.

Wellhead Attachments

Compact Gas Gun

The Compact Gas Gun consists of a microphone and a ten cubic inch volume chamber with a ¼” outlet valve. The outlet valve will open rapidly when the trigger is pulled. This generates a pressure pulse. If the pressure is greater in the volume chamber than in the casing annulus, a compression pulse is generated. If the pressure is greater in the casing annulus than in the volume chamber, a rarefaction pulse is created. A differential pressure must exist between the volume chamber and the casing annulus for a pressure pulse to be generated. The operator has the choice of using an explosion or implosion pulse.

Compression (Explosion) Pulse

Explosion utilizes an external gas supply to generate an acoustic pulse in the well. In the explosion mode, the volume chamber is charged from an external gas supply to a pressure in excess of the well pressure. Operating in the explosion mode keeps the inside of the chamber cleaner and results in less maintenance.

Rarefaction (Implosion) Pulse

If the well’s casing pressure is greater than 200 PSI, implosion can be used. This method uses the well’s pressure to generate a pulse. Use the gas gun filler/bleed valve to release gas from the volume chamber. An external gas supply is not necessary to operate in the implosion mode. Operation in this mode forces sand, moisture and other debris into the gas gun volume chamber and thus requires more maintenance including frequent replacement of “O” rings.

Description of Compact Gas Gun Control Functions (refer to drawing)

Volume Chamber Pressure Gauge

The volume chamber pressure gauge measures the pressure in the gas gun volume chamber. During normal operation, the volume chamber is charged to 100-psi more than the casing pressure. Use additional pressure if required for satisfactory results. If the internal gas valve is open, the gauge indicates the pressure between the gas gun and the casing annulus valve. If the casing annulus valve is open, the gauge indicates the casing pressure.

Casing Pressure Gauge Quick Connector

The quick connector is located on the side of the housing. A precision pressure gage having a range close to the pressure being measured will fit into the quick connector to enable the operator to obtain the casing pressure and casing pressure change with sufficient accuracy to perform calculations of producing BHP and casing gas flow rate.

Cocking Arm

The cocking arm is lifted to depress and close the valve between the gas chamber and the casing.

Casing Pressure Bleed Valve

This valve allows bleeding the pressure between the casing valve and the compact gas gun. Turn the knob counter clockwise to release the pressure. Verify that the casing valve is closed before opening the bleed valve.

Gun Filler-Bleed Valve

The filler-bleed valve is used to pressurize the gas gun volume chamber or to remove gas from the gas gun volume chamber. Gas is added to the chamber from a pressurized external gas source by insertion of mating quick connector, into the filler & bleed valve. Gas is bled from the chamber by rotating the knob clockwise. This action depresses the internal valve core and releases the gas from the volume chamber to the atmosphere.

Trigger Pawl

The Trigger Pawl is pulled to release the gas valve between the gas gun volume chamber and the casing. If sufficient pressure exists in the volume chamber or on the end of the gas valve, the gas valve will open.

Microphone

The microphone is a twin-disc pressure sensitive device that is vibration canceling.

Remote Fire Gas Gun

The remotely fired gas gun generates an acoustic pulse and detects the downhole reflections. The gas gun contains a volume chamber, which is filled with compressed gas to deliver the acoustic pulse to the well. A microphone housed in the gas gun detects the shot, collars and other wellbore reflections, and liquid level. The standard unit has a working pressure of 1500 PSI.

Gas Valve and Solenoid

The solenoid serves as a trigger mechanism to initiate the acoustic pulse. When energized, the solenoid lifts a small plunger and allows gas pressure to bleed off the top of the gas valve. Gas pressure then forces the gas valve open, causing an acoustic pulse to be delivered to the well as the gas flows from the volume chamber into the well, (see the remote fire gun diagram.) The gas valve does not hold pressure from the well. Therefore, gas pressure must be applied to the volume chamber inlet port in order to close it. Whenever the valve is left open, well fluids will flow backwards through the gun and into the volume chamber. This flow may entrain sand and other debris. These deposits may prevent the gas gun from operating properly. To minimize this potential problem, it is advisable to charge the volume chamber with clean gas before the casing valve is opened and as soon as the strip chart from any shot has been recorded. This will prevent the well fluids and debris from entering the solenoid gas valve mechanism and causing a malfunction of the firing mechanism.

Volume Chamber Pressure Gauge

The volume chamber pressure gauge measures the pressure in the gas gun volume chamber. It should be used to determine if the chamber pressure is sufficiently high (explosion mode) to generate the acoustic pulse. The volume chamber pressure should be approximately 100-psi in excess of casing pressure unless additional pressure is required to obtain desire results.

Casing Pressure Gauge or Optional Transducer

The casing pressure and casing pressure buildup during the acoustic test must be measured with an accurate and sensitive pressure gauge or sensor. The Remote Fire Gas Gun supplied with the Echometer Model M is equipped with a quick connect gauge that covers the range 0-200 psig. The user should consider the option of obtaining several gauges covering different pressure ranges.

Charging the Gas Volume Chamber

To charge the volume chamber, first connect the filler adapter to a 7.5 oz. CO₂ bottle. Then, press the adapter against the filler fitting on the gun. When these two fittings are pressed together, a valve core in the bottle is depressed and gas will flow from the bottle into the volume chamber. Charge the chamber to at least 100 PSI above casing pressure before attaching the gas gun to the casing annulus valve to prevent debris from entering the gas gun internal valve parts. The volume chamber pressure can be read on the gun-mounted gauge. A 5-LB, CO₂ bottle and hose with connector can be used to change the gun, if desired.

High Pressure Gas Guns

The 5000-psi gas gun is normally used in the implosion mode. It has an excellent noise-canceling microphone and generates a very good pulse when the ¹/₂-inch ball valve is opened rapidly and the well pressure exceeds 200-psi. When the 5000-psi gas gun becomes dirty due to debris imploding from the wellbore, the volume chamber and the microphone assembly can be easily flushed with a solvent. The 5000-psi gas gun requires very little maintenance. It is excellent for gas lift, flowing and high-pressure shut-in wells. It can be used in the explosion mode by charging the gas gun volume chamber to a pressure in excess of the well pressure.

The 15000-psi High Pressure Gas Gun operates in the implosion mode only. Excellent results have been obtained at pressures above 1500-psi through needle valves with 1/8-inch orifices, which are standard in most high-pressure wells.

For more details please refer to the Gun-Microphone Assemblies brochure in the appendix.

Accessories

Battery Charger (110 V- AC) or (220 V - AC if requested)

Automobile Battery Cable

Automobile Cigarette Lighter Cable

Casing Pressure Gauges

Precision Test Gauge

Precision Digital Gauge

Gas Cylinders

2-1/2 LB CO₂

5 LB CO₂

Nitrogen Cylinder

4 - Operation

Operation of the instrument is simple. First the acoustic wellhead should be attached to the casing annulus valve, and the cable connected between the microphone and the instrument. The valve between the casing annulus and the flow line should be closed to prevent the casing annulus gas from venting into the flow line causing excessive noise.

General Recording Procedure

When the power switch is turned on, a red LED light indicates that the battery is powering the electronics. The chart drive turns on and a header is printed as shown in Figure 3 in the appendix. Next, a system test is performed which also displays the battery voltage. If the battery voltage is low, a message to charge the battery is displayed. Then, the message is printed to "Turn on the chart drive to test well" and the chart drive stops until the chart drive switch is turned to the ON position. At this point the operator selects the type of collar response (filter) desired. Sharp upper collars can be selected for special applications such as shallow wells, irregular tubing length, dual tubing strings and other special applications. The lower collar position is selected for most deep wells especially with low casing pressure. Normally, both gain controls are set to the AUTO position and only changes from these settings are necessary for those cases when satisfactory recordings are not obtained in the automatic position. When the chart drive is activated, the form shown in Figure 4 is printed on the strip chart. This form is designed to insure that the operator will write all the pertinent information about the well and the test. This includes the well designation, the casing pressure, the casing pressure buildup rate and the latest well production test results. The universal coordinated time stamp is beneficial for tracking the sequence of shots and calculating the exact time interval between shots. The time interval is necessary when calculating rate of change in liquid level from which can be computed the well influx (or injectivity) rates or to compute pressure buildup rates. Next, the acoustic analysis form is printed on the strip chart. During the time that the forms are being recorded on the strip chart, the instrument measures the background noise on both channels and then analyzes the noise in terms of peak to peak amplitude and records the AUTO position when the chart drive is turned on, later adjustment of the gain control does not affect amplifier gain. Then, a message to generate the pulse is printed on the strip chart. When the shot is generated, the instrument detects the large signal and prints a vertical dotted line to mark zero time on the chart. Each second thereafter another mark is recorded and labeled with the corresponding elapsed time in seconds. If the “shot” is not detected by the electronics (which is indicated by the zero time mark), a larger pulse must be generated so that the electronics will detect the initial pulse. After the zero time mark is printed on the chart, operator adjustments of the gain control do not affect amplifier gain. This prevents the operator from increasing the gain, which might result in noise being mistaken for a liquid level kick. The operator turns off the chart drive after the liquid level response and other desired information is observed on the chart. The acoustic liquid level test can be repeated by reloading the gas chamber, turning on the chart drive, and generating another acoustic pulse. If the operator desires to manually select the amplifier gain, the gain control knob must be set at a value greater than one before the chart drive is turned on. The collar channel gain should be set so that the response is approximately 1/8 inch (3 mm) before the shot. The liquid level channel gain should be set so that the response is 1/16 inch (1 mm) before the shot. Operator adjustment of the gain control after the “shot” is detected and the zero time mark is recorded does not affect amplifier gain. If the recording level is excessive from downhole anomalies such as a tubing anchor or perforations, a lower gain setting should be used. Both channels may be set in AUTO gain setting mode or both in manual gain mode or one channel may operate in manual while the other is set to AUTO. Figure 5 shows two records. The upper record is with the filter setting on upper collars and the lower record shows the response when the filter setting is lower collars.

Operation of the Model M with the Compact Gas Gun

The compact gas gun is to be operated in the COMPRESSION (Explosion) or RAREFACTION (Implosion) mode. The operator should use the Compression (explosion) technique when the casing pressure is less than approximately 100 psig. The Rarefaction (implosion) technique may be used whenever the casing pressure is sufficient to obtain a good record.

COMPRESSION (EXPLOSION) MODE

Expansion of gas from the Echometer gas gun is used to generate a pressure pulse. The pressure pulse is positive since the gas chamber is charged to a pressure that exceeds the well pressure by at least 100-psi.

1. Securely attach the Echometer Gas Gun to the Casing Valve.

2. Close the Casing Pressure Bleed Valve and Filler Bleed Chamber Valve.

3. Lift the Cocking Arm to close the internal gas valve. This prevents debris from entering the volume chamber.

4. Open the Casing Valve to the Echometer Gas Gun slowly and Close the casing valve to the flow line.

5. Measure the Casing Pressure using the precision pressure gauge.

6. Record Time and Casing pressure.

7. Fill the volume chamber with gas (CO2 or N2) to at least 100-psi in excess of the Casing Pressure.

8. Connect the coaxial cable from the microphone to the Input of the Model M.

9. Turn Power Switch to ON.

10. Select the type of collar response desired and set the gain controls to AUTO.

11. Turn chart drive ON.

12. Generate pressure pulse by pulling Trigger Ring, after “Generate Pulse” is displayed on chart.

13. Turn chart drive OFF after detecting the liquid level signal.

14. Inspect the record and repeat the shot if the signal quality is not satisfactory.

15. Turn power switch to OFF after operation.

16. Record Time and Casing Pressure.

17. Close the Casing Valve between Echometer Gas Gun and the well.

18. Open the Casing Pressure Bleed Valve and release the pressure.

19. Open the Casing Valve to the flow line.

20. Remove the Echometer Gas Gun from the casing valve.

RAREFACTION (IMPLOSION) MODE

Gas is released from the well into the gas gun volume chamber to generate the initial pulse. Debris, moisture, corrosive liquids and chemicals, and other foreign material may be imploded into the gas gun volume chamber, which will increase maintenance requirements and may cause corrosion on the inside of the volume chamber.

1. Securely attach the Echometer Gas Gun to the Casing Valve.

2. Close the Casing Pressure Bleed Valve and Filler Bleed Chamber Valve.

3. Open the Casing Valve to the Echometer Gas Gun slowly and Close the casing valve to the flow line.

4. Pull Trigger Ring.

5. Lift the Cocking Arm to close the internal gas valve.

6. Measure the Casing Pressure using the precision pressure gauge.

7. Record Time and Casing Pressure.

8. Bleed the gas chamber pressure through the Filler-Bleeder Chamber Valve by rotating the knob clockwise until the gas gun pressure has decreased to approximately 200-psi below the casing pressure reading. Use greater or less differential pressure depending on the quality of the recording.

9. Connect the coaxial cable from the microphone to the INPUT of the Model M.

10. Turn Power Switch to ON.

11. Select the type of collar response desired and set the gain controls to AUTO.

12. Turn chart drive ON.

13. Generate pressure pulse by pulling Trigger Ring, after “Generate Pulse” is displayed on chart.

14. Turn chart drive OFF after detecting the liquid level signal.

15. Inspect the record and repeat the shot if the signal quality is not satisfactory.

16. Turn power switch to OFF after operation.

17. Record Time and Casing Pressure.

18. Close the Casing Valve between Echometer Gas Gun and the well.

19. Open the Casing Pressure Bleed Valve and release the pressure.

20. Open the Casing Valve to the flow line.

21. Remove the Echometer Gas Gun from the casing valve.

Operation of the Model M with the Remote Fired Gas Gun

The main differences in operating procedure are that the Remote Fired Gas Gun initial pulse is generated by depressing the Remote Fire Button on the control panel, and that this gun can only be used in the Compression (Explosion) Mode.

1. Securely attach the Echometer Remote Fire Gas Gun to the Casing Valve.

2. Charge the gas chamber to at least 100-psi in excess of the estimated well pressure to prevent debris from entering the volume chamber and the solenoid dart valve assembly.

3. Close the gas gun's Casing Pressure Bleed Valve.

4. Open the Casing Valve to the Remote Fire Gas Gun slowly.

5. Close the casing valve to the flow line.

6. Measure the casing pressure using the precision pressure gauge.

7. Record Time and Casing Pressure

8. Verify that the volume chamber pressure is at least 100-psi in excess of the Casing Pressure.

9. Connect the coaxial cable from the microphone to the Input of the Model M.

10. Connect the remote fire cable from the gun to the REMOTE FIRE connector.

11. Turn Power Switch to ON.

12. Select the collar FILTER and set the gain controls to AUTO.

13. Turn chart drive ON.

14. Generate pressure pulse by depressing the Remote Fire button for approximately one second to insure full opening of the solenoid valve.

15. Turn chart drive OFF after detecting the liquid level signal.

16. Inspect the record and repeat the shot if the signal quality is not satisfactory

17. Turn power switch to OFF after operation.

18. Record Time and Casing Pressure.

19. Close Casing Valve to the Remote Fire Gas Gun.

20. Open the Casing Pressure Bleed Valve and release the pressure.

21. Open the Casing Valve to the flow line.

22. Disconnect cables and remove the Echometer Gas Gun from the casing valve.

NOTES

1. On deep, low pressure wells; first select the lower collar position.

2. If the initial pulse is not detected which is indicated by the zero timing mark, use a larger initial pulse.

3. If the liquid level is not detected (especially in deep wells with low casing pressure), the volume chamber pressure should be increased in increments of 300-psi up to the limit of the available gas supply.

4. Do not use a larger volume chamber pressure than needed. Operating the gas gun at 300-psi requires twice as much gas as when operating at 150-psi. Only one half as many shots will be obtained from a gas cylinder.

5. When using CO₂ gas above 300-psi (at normal temperatures), liquid may form in the gas gun, which will result in considerably more gas being used per shot.

6. When using nitrogen gas, use a regulator so that the pressure will not exceed the working pressure rating of 1500-psi.

Recommendations for Optimum Performance

The Echometer wellhead should be as near as possible to the casing annulus (or the tubing) preferably within 5 feet. Short (5-10 ft) lengths of pipe can mask the desired downhole signals. Longer (20-60 ft) lengths will generate multiple reflections, which are hard to distinguish from collar reflections. Use a minimum of 90⁰ ells and tees and direct the blast straight into the well if possible. Two-inch connections are recommended, but one inch connections are generally satisfactory if the length of 1 inch pipe is kept to a minimum.

Proper sensitivity setting is very important. Select the AUTO gain setting for the first shot. The background noise level is indicated on the chart. Surface vibrations, leaking gas connections, gas “popping” out of the gas/liquid interface and other unstable conditions, cause this noise. This background noise is not a part of the signals when the pressure wave is generated. The instrument will automatically record the background noise at a low level and larger collar and liquid level signals will be recorded at larger amplitudes, which simplifies the interpretation of the chart. When operating in the AUTO mode, adjusting the sensitivity after the chart drive is tuned ON does not change the automatic gain selection made by the electronics and software.

The pressure pulse travels down the well and is reflected by tubing collars and the liquid level. The signals from upper collar reflections are strong, but the collar response becomes weaker as the pressure pulse travels long distances to the bottom of the well so that the reflections from the lower collars may be weaker than the background noise. The liquid level reflection varies from a strong signal in a shallow high pressure well to a very weak signal in a deep low pressure well. Only signals stronger than the background noise are meaningful in the recording. It is obvious that strong background noises must be reduced if the recording of lower collars and liquid level is to be obtained.

Background noise can be classified as surface mechanical vibration noise or acoustic noise. The source of noise can be determined easily by increasing the sensitivity until signal deflection is obtained. Closing the casing valve between the microphone and the annulus will cause a reduction in the noise level if its source is acoustic noise. If the signal level remains the same, then the noise is caused either by surface vibrations or by gas leakage from extraneous lines connected on the same side of the closed casing valve as the microphone. The microphone is shock mounted, but if the wellhead attachment vibrates excessively, unwanted signals are generated. Wellhead vibration result from running gas engines, chattering check valves and other reciprocating surface equipment. It may be necessary to eliminate wellhead vibrations to obtain better quality records in deep low-pressure wells. All other lines leading to the casing annulus should be closed.

The main source of down-hole acoustic noise is gas "popping" out of a gaseous annular liquid column or liquid falling into the wellbore. Downhole noise can also result from tubing and casing leaks. Generally, the down-hole acoustic noise can be reduced in relation to the desired reflected signals by causing an increase in the casing pressure. In order to do this, continue to pump the well with the casing vent valve closed. At low pressures, an increase of 10-psi in the casing pressure almost always improves the record and it only depresses the liquid level by 30 feet.

If the signal from the liquid level is not detected due to excessive surface vibration noise or down-hole acoustic noise, a larger signal from the liquid level can be obtained by generating a larger initial pressure pulse. Also, increasing the sensitivity so that the background noise level exceeds 1/8 inch, generally will make interpretation much more difficult and is not recommended.

Automatic Gain Setting (AGS) Mode Characteristics

The Echometer Model M uses a microprocessor, which is programmed to evaluate the signal level before the shot and set the amplifier gain as necessary to optimize the quality of the recording. The