Acoustic Techniques to Monitor and Troubleshoot Gas-lift Wells

Transcription

1 37 th Gas-Lift Workshop Houston, Texas, USA February 3 7, 2014 Acoustic Techniques to Monitor and Troubleshoot Gas-lift Wells Carrie-Anne Taylor, Engineer Lynn Rowlan, Engineer Echometer Company Feb. 3-7, Gas-Lift Workshop 1

2 Introduction The distance to the fluid level provides beneficial information throughout the life of a gas-lift well. Fluid level depths with respect to valves Depth to the deepest mandrel uncovered Verify Unloading process is proceeding properly Find holes, restrictions Wellbore problem or equipment malfunction? How can acoustics aid in Troubleshooting? Feb. 3 7, Gas-Lift Workshop 2

3 Determine Fluid Level Depths with Respect to Valves **BP Homa A-1 Casing IMP (08:04:01) Wellbore Overlay The fluid level is quickly and easily identifiable between the 9 th and 10 th Gas-lift Valves. Liquid Level

4 Acoustic pulses reflect off gaslift valves and other anomalies. GLV 1 GLV 2 GLV 3 GLV 4 GLV 5 GLV 6 GLV 7 GLV 8 GLV 9 LL Not all markers exactly line up with their respective reflections. Acoustic Velocity changes with respect to pressure and temperature as the depth of the wellbore increases. Gas-lift Valve Depths from Wellbore Schematic: GLM GLM GLM GLM GLM GLM GLM GLM GLM GLM Gas-Lift Workshop 4

5 Acoustic Velocity Between Downhole Markers Feb Gas-Lift Workshop 5

6 Acoustic Velocity Profiles in Gas-lift Wells Depends on: 1. Gas gravity / composition 2. Temperature along wellbore 3. Pressure profile in well 4. Can be determined from counting collar echoes or identifying downhole markers detected during a shot 5. Uniform Gas Composition when Gas is Flowing 6. Acoustic Velocity Usually Increases with Depth Due to Higher Temperature 6

7 Gas-lift Mandrels are Excellent Downhole Markers Purpose Accurately calculate the distance to the liquid level plus other downhole reflectors such as gas lift valves and mandrels, tubing collars, subsurface safety valves and possible holes or other problems. Distances Determined using echoes from gas-lift valves at known distances from the wellhead. Accounts for Variations of acoustic velocity commonly observed in most wellbores due to variations of temperature, pressure and gas composition as a function of depth. Feb. 3 7, Gas-Lift Workshop 7

8 Downhole Markers for Accurate Acoustic Velocity and Fluid Level Analysis Apply Low Pass Filter to reduce high frequency noise and see detail. Feb. 3 7,

9 Wellbore Schematics Provide Downhole Markers 9

10 Acoustic Velocity is Calculated Between Markers Along the Shot Trace S

11 If the Acoustic Velocity is out of Range, THERE IS A PROBLEM Awareness of the calculated Acoustic Velocity is important: Quality check for correct marker selection. Accurate fluid level calculations. Verify gas gravity and uniform gas composition in the well. Acoustic Velocity typically displays an increasing trend in producing gas-lift wells. Feb. 3 7, Gas-Lift Workshop 11

12 Direction of Kick Across Mandrels Feb Gas-Lift Workshop 12

13 Shape and Direction of Echoes from Valves and Mandrels Two factors determine the direction of kick of Gas-lift Mandrels on the acoustic trace: 1) Physical characteristics of the mandrels 2) Is the operator shooting down the tubing or the casing? On the casing side, the mandrels take up space within the annulus, resulting in a downward reflection kick. On the tubing side, the recess within the mandrel where the valve is located results in an upward reflection kick. Feb. 3 7, 2014 Photo: courtesy of Lufkin Industries Tubing and Casing acoustic traces can be overlaid for comparison and troubleshooting Gas-Lift Workshop 13

14 Mandrel Design Determines Direction of Kick Shot Down Tubing Displays Upkick at Mandrel Increase in area = Upkick Shot Down Casing Displays Downkick at Mandrel Decrease in area = Downkick

15 mv Overlay Casing and Tubing Shots for Troubleshooting Sec Tubing Shot Casing Shot Ft Can help identify problems by answering questions: Do the mandrel reflections line up? Are there additional upkicks or downkicks indicating possible holes, restrictions or other problems? Feb. 3 7, Gas-Lift Workshop 15

16 Problems in the Tubing String Feb Gas-Lift Workshop 16

17 Upkick Identifies Hole in Tubing Fluid Level

18 Compare Shots Down Tubing & Casing Hole in 6868 Tubing Shot Casing Shot

19 Compare Shots Down Tubing & Casing LL Tubing LL GLV9 Casing 19

20 Compare Shots Down Tubing & Casing Overlaying the Tubing and Casing shots based on time verifies an upkick at the hole in the tubing in both shots. The Depth Reference line gives an accurate depth to the hole of 1083ft. Feb. 3 7, Gas-Lift Workshop 20

21 Fluid Levels During Unloading Sequence Feb Gas-Lift Workshop 21

22 Acoustics Provide Valuable Details During Unloading Sequence Shots down the Casing Annulus provide a quick look at uncovered mandrels as the annular fluid level drops during the Unloading process. The operating valve is quickly and easily identified. Or the depth to the deepest valve above the annular fluid level, when checks valves are present. GLM 1 GLM 2 GLM 3 GLM 4 LL

23 Troubleshooting a Problem Well Feb Gas-Lift Workshop 23

24 9:53am LL 174.7psi 162.8psi 144.8psi 89.8psi 169psi 155psi 10:00am GLV1 LL 10:05am GLV1 GLV2 LL 10:18am GLV1 GLV2 GLV3 LL 10:44am GLV1 GLV2 GLV3 GLV4 LL 11:12am GLV1 GLV2 GLV3 GLV4 EOT LL

25 Fluid Levels fluctuate with an increase or decrease in tubing pressure Fluid Level Depth Tubing Pressure

26 Horizontal Gas-Lifted/Plunger Lifted Well Feb Gas-Lift Workshop 26

27 Stratified Gas Flow Regimes Exist in Horizontal Gas Wells 1. The ability to see past the end of the tubing is unusual in a vertical plunger lift well, because the liquid level is normally at the end of the tubing. 2. In horizontal wells, stratified flow exists; it is not uncommon to see features in the wellbore in the horizontal section past the end of the tubing. 3. Horizontal section appears to be relatively dry (no liquid level); but a significant amount of liquid enters the tubing. Feb. 3 7, Gas-Lift Workshop 27

28 Overlay Wellbore Profile Quick placement and verification of: Gas-lift valves and mandrels End of the Tubing Perforation Intervals Feb. 3 7, Gas-Lift Workshop 28

29 Horizontal Plunger Lifted Well GLV 1712' GLV 3014' GLV 4092' GLV 4797' GLV 5256' GLV 5716' GLV 6176' GLV 6570' GLV 7031 The fluid level is at a measured depth of 9118ft. Gas-lift Valves can be used to confirm the end of the tubing and the top of the perforations. 29

30 Reflections can be identified to the Toe Due to Stratified Gas Flow in the Horizontal section of the well. Perf LL EOT The top perforation upkick used to determine the depths in the well.

31 Conclusion Beneficial information is obtained throughout the life of a gas-lift well by determining the distance to the fluid level. Knowing the Acoustic Velocity profile of a well provides critical information for verifying gas composition and fluid level accuracy. Identifying reflection kicks across valves and mandrels result in more accurate depth analysis. Operating valves are identified quickly and easily. Troubleshooting techniques aid in identifying downhole problems. Feb. 3 7, Gas-Lift Workshop 31

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