Optimum Performance in Dual Gas-Lift Wells

1. Optimum Performance in Dual Gas-Lift Wells ASME/API/ISO Spring 2004 Gas-Lift Workshop February 10-11, 2004

2. Dual gas-lift design • Design goals - lift as deep as possible Single point injection through the bottom valve Or inject through two of the bracketing valves Multi-point injection must be at stable injection rates and at the deepest possible locations.

3. Unloading a dual • Follow the API unloading procedure. • Be patient. There are no shortcuts to the unloading procedure that will safely speed up the unloading process.

4. Unloading a dual Build the casing pressure no faster than 50 psi per 10 minutes

5. Surveillance • SCADA • 2-pen charts • Well tests • Flowing pressure surveys • Static pressure surveys • Acoustic sounding device

6. Typical dual gas-lift problems • Higher backpressure than the original designed conditions. • Lower injection pressure than the original designed conditions. • Higher injection pressure than the original designed conditions. • One string will not take injection gas or takes less than the designed rate. • One string has pressure depleted and is shut-in. • One string taking more injection gas than its designed rate. • Producing Emulsions • Tubing-casing communication

7. Proving tubing-casing communication Communication Above Tubing Fluid Level As the casing is bled down, the tubing with the communication problem will loose pressure and gradually equalize with the casing pressure.

8. Proving tubing-casing communication Communication Below Tubing Fluid Level Monitor the casing fluid level during bleeding operations As the casing pressure is bled down, the casing fluid level will rise as tubing fluid enters the casing. A formation with high feed-in ability will maintain a constant tubing fluid level as it fills the casing during the bleed-down. No change in tubing pressure will be observed.

9. Locating the communication point Slickline log – Temperature, spinner, pressure, CCL Dependable only if steady flow can be achieved Can sometimes find multiple leaks or holes. Holefinder – Use if steady flow cannot be achieved. Good for locating the top hole. Not good for multiple holes. Caliper survey – Can find multiple holes. Will not locate leaking gaslift mandrels. Ponytail – You must have a good flow rate across the hole to locate it. Not as dependable as other methods.

10. Dual gas-lift troubleshooting • Compare the initial design parameters with the actual operating parameters. • Obtain individual well tests with the other string shut-in. • Conduct tubing integrity tests while monitoring the casing fluid level. • Design and run a flowing gradient survey with a build-up. • If a gas-lift valve revision is necessary, use as many dummy valves as possible. High productivity wells with relatively high formation GLR’s will sometimes unload and transfer to a shallower point of injection as the production rates increase.

11. Wireline procedures for dual gas-lift Running valves • Keep both sides of the dual shut-in when a gas-lift mandrel has a vacant pocket. • Pulling a gas-lift valve in a dual will give the reservoir a flow path to the casing and through the gas-lift valves of the other string. Dummy valves in the other string • The wireline procedure is the same as running valves in a single completion. Live valves in the other string • Take precautions to prevent the well from flowing into the other string during the valve revision

12. Wireline procedures for dual gas-lift • Installing valves in the string with the lowest pressure Use the same wireline procedure as for single completions • Installing valves in the string with the highest pressure Prevent the high pressured zone from flowing into the low pressure zone during the valve installation • Tubing Integrity test Monitor the casing fluid level during the tubing integrity test.

13. Pulling valves in a dual The casing and tubing pressures are equalized with gas-lift pressure Pulling the bottom valves in the long string will result in the long string filling the casing with fluid. The fluid will then pass through the gaslift valves on the short string.

14. Pulling valves in a dual A standing valve is set in the lowest pressure side of the dual and the tubing is filled with water. This prevents cross-flow from occurring

15. Avoiding wireline problems • Always have a detailed wireline procedure completed before pulling valves • Minimize wireline time but don’t take short-cuts • Utilize dummy valves in valve re-designs when possible • Be aware of the size of the tool deflector in the sidepocket mandrel. • When running valves, use two brass pins in the running tool • Prevent the higher pressured zone from flowing into the low pressured zone • Catcher subs on kickover tools • Perform tubing integrity tests monitoring the casing fluid level after every valve revision

16. Dual flowing surveys Long String Short String

17. Dual flowing surveys Long String Short String

18. Flowing surveys in heading wells Maximum pressure reading Minimum pressure reading SBHP = 2040 psi x

19. Flowing surveys in heading wells

20. Slickline log – Temperature, Pressure, CCL

21. Slickline log – Temperature, Spinner, CCL