1. Gaslift Management in PDO Northern Directorate
By Walrick van Zandvoord

2. Gaslift Management in PDO Agenda
Introduction
Designs, Improvements, Opportunities and challenges
Gaslift management and processes
Automatic Validation Tester (AVT) and Wireless gaslift trial
Overview per area and examples
Conclusion

3. Location Country size similar to Kansas Population 2.5 million
Accelerated development
75 % income depends on hydrocarbon

4. People

5. People

6. Beaches & Wadis

7. PDO (since ‘66) is a JV between 60 % Government of Oman 34 % Shell
MUSCAT
Sur
Sohar
Salalah
ARABIAN SEA
GULF OF OMAN
100 km
PDO (since ‘66) is a JV between
60 % Government of Oman
34 % Shell
4 % TotalFina
2 % Partex
Shell is technical advisor
Production 700 kb/d (90% of Oman’s
Oil production)
66 producing stations
117 oil producing fields
Over 3000 active wells
620 gaslift strings. 28% of production, ,000 bbl/d
85% of gaslift production from North
Majority of fields under water flood

8. Gaslift wells in the Northern Directorate
The North of PDO has primarily carbonate reservoirs with depths varying from as shallow as 800m to 2700m deep.
Now there are approximately 500 Gaslift wells constituting 50% of the oil producers.
In the North, Gaslift wells produce 45% of the oil and 42% of the gross.

9. Design
Design in most wells has 2 to 5 mandrels, depending on well depth and expected deepest operating point
IPO valves are run in >95% of the wells
Mostly unloading valve sizes are the same as operating valve size to allow the operating point to be the orifice or unloading valve.
Redesigns are done where well behaviour becomes too unstable

10. Operating @ mandrel 2 (through unloading valve)
Initial Performance
mandrel 2 (through unloading valve)
Future Performance after on-stream of Water Injector
mandrel 3 (through unloading valve)
Later Performance
mandrel 4

11. Optimisation and Challenges
Well by Well
Unstable wells
Leaking valves or tubing
Well integrity (e.g. liftgas injected in shallow aquifers)
Possibility to lift deeper
Scale clean outs
Group optimisation
Surface controlled gaslift rates through SCADA / DCS
Set-points based on optimal distribution of liftgas using WinGLUE
Tables are created for different compressor availabilities for optimal distribution.

12. Optimisation and Challenges
Group optimisation - Continued
Optimally distribute
Minimise deferment when compressors are down
Challenges
Gas measurements are of insufficient quality. Flowing surveys are therefore essential
Well integrity problems are experienced in some areas, e.g. tubing leaks, mandrel leaks, casing leaks

13. Optimisation and Challenges
Challenges - Continued
Long integrity repair jobs
Well integrity problems has Impact on well models
Continuous changes in the reservoir pressure, PI, water cut etc.
The dynamics of reservoir not captured in well models.
Young & bright, but in-experienced production engineers.
Solutions
Dedicated production engineers on well integrity
Surveillance engineers responsible for only wells in total
Intensive training and bringing in coaches

14. Process Dedicated gaslift process
Monitor and trouble shoot using SCADA and test data
Understand the problem and correct
Further investigation
Analyse results of investigation
Determine improvement potential, costs and justify activity.
Design new gaslift string and schedule activity
Set valves, check valves with AVT tester, test old valves and feedback
Kick off the well and evaluate the results
Review and file report

15. PDO Gaslift Management Set-up

16. Process Improvements
WinGLUE gaslift QC database set up
Automated links
Central storage of gaslift analyses
Most wells available in the SCADA system (RTAP / SOFS or the latest PC based FIELDWARE).
AVT tester is used for QC valves before running and recently also pulled valves

17. Decker’s Automatic Validation Tester (AVT )
Implemented in the well services workshop
TROP, stem travel, R ratio etc.
Rejected at agreed tolerances, e.g. TROP difference < 15 PSI
>25% of the valves were rejected on TROP.
Visible improvements

18. Decker’s Automatic Validation Tester (AVT )
Testing of pulled valves just started. >60% fail on leaking bellows.
Keep track of a “problem log” to increase understanding
Network connection is essential
Staff in the well services more conscious

19. Specific Overview per Area Area L
Constrained due to flaring restriction (no compressor ullage)
Workshop was organised
Deliverables of the workshop:
Coaching / training
Saving of 3.6 million scf/d of liftgas
Well integrity problems found and repaired
Detailed gaslift surveillance was carried out and many wells were stabilised
Many gaslift measurements wrong and corrected
For 2003 the estimated impact on production is approximately around 1200 bbl/d.

20. Specific Overview per Area Area Q
In Area Q, test data quality is an issue
Some wells were found quit based on flowing surveys
Some wells found with scale obstruction. Cleaned out and restored.
Total increase in the Area Q was 600 bbl/d or 10% of the total gaslift production. 3% 2002 year average impact.

21. well 110 Well was tested at 2000 bbl/d net oil, low BSW through 3 1/2”
200 bbl/d gain from switching on gaslift
Theoretical pressures
Tubing upsize was expected to double production
Flowing survey could only be matched with 800 bbl/d less and tubing upsize was canceled
Actual pressures

22. Specific Overview per Area Area F
Area F consists of two large fields
Field N has mostly natural producers.
Flow limited by Gas Oil Gravity Drainage (GOGD)
N compressors are full. Cutting back liftgas looked at.
Field F is partly water-flood and partly GOGD
Workshop held. Opportunities found:
Reduce liftgas consumption to free up compressor space (cutting back lift-gas, running velocity strings, 3 1/2” to 2 7/8” tubing)
Many wells without RTU’s

23. Area F Wireless Gaslift Valves Trial
Wireless gaslift valves (2) were installed in a well in Field F in 2002.
Communication through a modem with PC in CCR and Main Office
Down-hole pressures and temperatures displayed
Full control from the desktop was achieved
Live optimisation
Modem on bottom valve broke down, but still operating.
Confirmed bad batch of modems (50%)

24. Area F Wireless Gaslift Valves Trial
Business case for large scale implementation being made, but
times higher costs than conventional gaslift
Even with one third of costs, large scale implementation means 12,000,000 bbl or 16,000 bbl/d extra production is required or 8% of production.
Most promising to replace PPO valves

25. Specific Overview per Area Area Y
Advanced automation; Gaslift control valves linked to the DCS & SCADA. Full control and optimisation.
Main challenge is well integrity and continuously changing well performance.
Additional people have been put on the job in Area Y (surveillance engineers). They complement the work of the other production engineers.
Coaches brought in

26. Specific Overview per Area Area Y - Well Examples

27. Specific Overview per Area Area Y - Well Examples

28. Benefits Reduction in Liftgas usage (~2.5 mln m3/d)
Cost savings on Gaslift compressor requirements.
Enabled production of high GOR wells
Create compressor capacity to handle new oil producers.
Stabilising wells
In some cases lifting deeper
Sum of the measurable initial production increases after activities in 2003 is around 4500 bbl/d (2% of total North) with. Year average value is 0.7%.

29. What is happening next …..?
Further enhance staff competence and skills
Complete implementation of the AVT tester
Trial new technology such as Bubble breaker, Bubble gaslift and surface controlled gaslift valves
Bringing in a dedicated production engineer for gaslift
Continue with the efforts, because it pays back.