35 th Gas-Lift Workshop Houston, Texas, USA February 6 10, 2012 Anomaly Marker Method for Gas-Lift Wells Carrie-Anne Taylor, Echometer Company Lynn Rowlan, Echometer Company Feb. 6-10, 2012 2012 Gas-Lift Workshop 1
Anomaly Marker Method Purpose Accurately calculate the distance to the liquid level plus other downhole reflectors such as gas lift valves, 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. 6-10, 2012 2012 Gas-Lift Workshop 2
Anomalies are Markers in the Well at Known Distances Anomaly distances are entered as Well Marker Info Initially based on an estimated acoustic velocity, tick marks along the depth axis are located at distances that would correspond to the location of the anomaly echoes. Anomalies don t match echoes, relocates each tick mark to match exactly the beginning of the echo for a specific anomaly. Anomaly echoes are fixed to known depths by starting from the first anomaly, then from the first anomaly to the second anomaly and so on until the distance to the liquid level is accurately determined. Feb. 6-10, 2012 2012 Gas-Lift Workshop 3
Computed Distance to Liquid Level Distance to the liquid level is computed: Start at distance to deepest anomaly Last interval distance to liquid level equals Acoustic Velocity * Time/2 Add anomaly distance plus interval distance to liquid level LL = DA + ((RTTT from DA to LL*AV)/2) Feb. 6-10, 2012 2012 Gas-Lift Workshop 4
Anomaly Example Noisy Initial Acoustic Trace With Anomaly Echoes Collars Anomaly Echo Feb. 6-10, 2012 2012 Gas-Lift Workshop 4
See Echoes Better by Removing Noise From Acoustic Trace Scale up trace to see better.
Identify/Select Correct Liquid Level Echo Move the LL marker to the knee of the kick.
Liquid Level Depth is Approximate
Known Depth of Anomalies
Make Depth Accurate by Identifying Each Anomaly SSSV
Next Anomaly Automatically Selected At first glance, it appears the automatic pick of marker is a little to the left of the kick.
Fine Tune Location of Selected Anomaly But we also see a kick to the left of the marker. Some quick calculations tell us that this is not a repeat. Select Interval Left to get a clear picture of the reflection located just below the 6 second mark.
Examine the Acoustic Trace and Select Correct Echo This is a much more likely position for the placement of the next marker.
Continue Down Trace Selecting Anomaly Echoes If the correct marker is not selected, then move window to see the marker echo.
Continue Down Trace Selecting Anomaly Echoes
Continue Down Trace Selecting Anomaly Echoes Scale UP if needed to verify that this is the last marker before the liquid level.
Anomaly Echoes Below the Liquid Level are Negligible Gas Lift Mandrel 8 and the Packer are below the liquid level marker so these last two markers can be skipped.
Accurate Distance to Liquid Level Using Anomaly Depths
Old Reliable Paper Strip Chart S 1 2 3 4 5 6 LL Must Analyze by Hand Calculating Depths and Acoustic Velocities
Sometimes, the liquid level is not immediately obvious. It is then necessary to identify the kicks down the shot trace. What to look for: Repeating echoes Repeating time intervals Whether kicks are going up or down Rate of reflection echoes on high liquid levels Wellbore Schematic Important!!! Feb. 6-10, 2012 2012 Gas-Lift Workshop 20
Can Be Confusing Due To Lots of Echoes and Repeats 8.340 9.100 9.860 10.620.760.760.760.760 Casing Liquid Level Feb. 6-10, 2012 11.645 12.405 11.380 12.140 13.025.760.760 2012 Gas-Lift Workshop LL 21
Analysis Considerations 1) Sound reflection hits the liquid level, indicating a decrease in cross-sectional area which will show up as a downward kick on the shot trace. 2) Make sure the marker is placed at the knee of the kick the moment the kick begins its downward movement. 3) If markers have not yet been placed, the liquid level depth may reflect an unreasonable result. Place the marker at the appropriate kick, then place the anomaly markers. Feb. 6-10, 2012 2012 Gas-Lift Workshop 22
Reflections after LL In almost every case, it is not possible to see below the liquid level. Any echoes showing up after a liquid level are repeat reflections. Always identify and eliminate echoes that are repeats. All anomalies can repeat. Example of repeats below liquid level. LL Feb. 6-10, 2012 2012 Gas-Lift Workshop 23
Conclusion New Technology Does the Calculations on the Acoustic Trace for You Identifying Anomaly Echoes is Simplified Marker Depths are Automatically Determined Manual Adjustments Required For Accuracy Data is digital and not on a Strip of Paper, so Safe Backup of Information is Done Recall of Data and Re-analysis is a Straight Forward Process Feb. 6 10, 2012 2012 Gas-Lift Workshop 24
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