Gas Lift Redesign in Dual Strings Completion

1. Gas Lift Redesign in Dual Strings Completion Wahyu Jatmiko ( BP-Indonesia ) Herry Subekti ( BP-Indonesia ) Gatut Widianoko ( Weatherford ) Presented by Henry Nickens, BP-America, Houston

2. Gas Lift Redesign : To change setting pressure and port size of gas lift valves, unloading and operating valves, at existing mandrels.

3. BP West Java Well Work Perforation Sand Clean Out Matrix Stim Scale Clean Out WSO Gas Lift Choke Opt Zone Change

4. West Java Field Overview • West Java Reservoir Overview • West Java Dual Completion • Why redesign gas lift • Process flow to redesign gas lift valves • Summary

5. West Java Overview • BP-West Java area is located offshore of the north of Java Island in Indonesia. • Initial oil production was in 1971. • West Java field covers an area of some 18,000 square-kilometers with total wells • around 700. • 75% of total wells are producing under gas lift system. • Current production rate of 40,000 BOPD and 300 MMscfd of gas • (~ 75 bopd/600 Mscfd per well)

6. Cisubuh shales -1,000 ft shallow gas Parigi Limestone -2,000 ft Pre-Parigi LL- 32 LL- 33/35 LL- 37 LL- 39 LL- 40 LL- 41 LL- 44 -3,000 ft Main -4,000 ft Massive Batu Raja Limestone -5,000 ft Talang-Akar LL- 57 to LL- 64 -6,000 ft Basement West Java Reservoir Overview • West Java reservoir is multi stacked sandstone and carbonate reservoir. • Mostly oil was producing from main, massive, baturaja and talang akar formation. The rest of formation are gas producing. • Liquid productivity index is 1-5 bbl/day/psia, average TGOR of 500-1000 scf/stb and current liquid production about 500-1000 BLPD. • No reservoir pressure maintenance

7. West Java Dual Completion • optimise oil production • avoid cross flow • be able to allocate production data • perform well work • do reservoir monitoring Dual completion was selected to :

8. Why redesign gas lift valves Periodically gas lift valve design is needed to : • maintain liquid production due to declining reservoir pressure. • response to the change of gas lift source pressure. • increase gas injection rate due to increasing water cut. • solve gas lift robbing problem Liquid production keep declining GLV redesign was done

9. Process flow to redesign • Survey current gas lift performance • Obtain field and reservoir data • Matching well test to estimate - gas oil ratio - productivity index • Redesign for best point of injection, setting valve pressure • Optimize injection rate on short and long string

10. Process flow to redesign Survey current gas lift performance Gas lift gradient survey should be done prior to redesign gas lift to make sure there is no leaking in the tubing and to check gas lift performance. Dummy valves are leaking (~ 20% of wells)

11. Process flow to redesign • To redesign gas lift, the following data is required : • Current reservoir pressure data • Flowing gradient survey • Well test data • Latest gas lift valves report • Setting pressure report • Productivity Index • Latest gas oil ratio Field and Reservoir Data

12. Process flow to redesign Matching well test • Stable well test is selected for well test matching. • For the dual completion, well test data does not give gas lift injection rate data.

13. Process flow to redesign To estimate productivity index, well modeling is built using nodal analysis with the input : total liquid water cut flowing tubing pressure total GLR reservoir pressure Injection rate estimated from Qgas,inj = Qgas,total – GORform x Qoil Sensitivity on productivity index is performed to match liquid rate with well test. Matching well test

14. Process flow to redesign Productivity index from well test matching is used to estimate gas oil ratio. If GORform not available, then sensitivity on GLR until no intersection between IPR and tubing hydraulic was reached. Then, current gas oil ratio could be calculated based on the result of the GLR sensitivity. Matching well test Gas liquid ratio with no intersection, GOR = GLR*Liquid/oil

15. Process flow to redesign Design best point injection and setting pressure Optimum injection rate Short Long Once productivity index and gas oil ratio could be estimated, the gas lift curve is generated to determine optimum gas injection rate.

16. Process flow to redesign Design best point injection and setting pressure

17. Process flow to redesign Design best point injection and setting pressure

18. Process flow to redesign Spreadsheet to check valve performance after new design is installed. Dual strings gas lift injection rate optimisation

19. Process flow to redesign Gas robbing potentially occur Case I (operating valve depth and flowing tubing pressure are similar ) To avoid gas robbing use similar port size

20. Process flow to redesign Gas robbing potentially occur Case II (operating valve depth and flowing tubing pressure are not similar ) Use different port size to avoid gas robbing

21. Process flow to redesign Example Redesign Result

22. Process flow to redesign Well Test after and before gas lift redesign Example Target: 6 redesigns/month Production ~ 80 bopd increase Injection Gas ~ 200 mscf/d decrease

23. Summary • Uncertainty on gas lift injection rate each string, current gas oil ratio and productivity index in dual strings completion could be estimated using nodal analysis. • It is difficult to reach optimum gas lift injection rate in both string as gas injection rate in both string should be balance. • Gas lift robbing is the main problem in dual completion but it could be avoided by: • using similar port size in both string when flowing tubing pressure and operating injection point depth are similar. • using different port size between short and long strings when flowing tubing pressure is different. • Ideally, gas lift gradient survey is performed regularly to prevent gas lift robbing.

24. Contact for further information: Wahyu Jatmiko wahyuj@bp.com