1. Gas Lift Design Philosophy for Chevron’s Subsea Developments
Shauna Noonan, Completions Engineering Team
Chevron Petroleum Technology Company
Houston, Texas
Good Morning. It's nice to be back home.

2. Presentation Outline Single Point Injection (pros and cons)
Understanding the Stability Issues
Using Transient Programs
Field examples:
Kuito / Benguela-Belize-Tomboco fields, Angola
Hebron Field, East Coast Canada
Alba field, North Sea
Example of “What’s Not Recommended”
Questions
Chevron is not a huge heavy oil producer but we do have areas that we have operated in for quite some time. The three main areas are Venezuela, Indonesia and California. We do have some heavy stuff in the Brooks area but I thought you have seen past presentations on that so I threw in Hebron for a quick discussion.
In order to squeeze this presentation into 30 minutes, I will focus on operating practices and downhole equipment that is working well for us. I could talk for days on all the things we tried that did not work. If you want to know more details than what is presented here, catch me sometime during the next few days and I will be glad to discuss them with you.

3. Single Point Injection Using Orifice
Pros
higher reliability than conventional completion using live valves
meets “zero intervention” philosophy set for Chevron’s subsea developments
Cons
requires a minimum gas injection rate for well stability
requires a higher injection pressure
valve erosion becomes a serious issue

4. - general comments heard from various Chevron engineers
The Challenge...
“Size the downhole orifice as big as possible and we can just control the gas injection rates from the FPSO”
- general comments heard from various Chevron engineers
THE DOWNHOLE CHOKE (aka orifice) CONTROLS THE RATE OF GAS INJECTION INTO THE TUBING, NOT THE SURFACE CHOKE!!!!!!!!

5. Gas Lift Stability
For a single point system, there is a minimum surface injection rate required for the orifice to maintain sufficient annular backpressure (i.e. casing pressure consistently higher than the flowing tubing pressure) for continuous downhole gas injection.

6. Minimum Injection Rates
This minimum injection rate is a function of orifice size and flowing tubing pressure (aka wellhead pressure, PI, reservoir pressure, watercut, etc)
What does happen at rates lower than this minimum injection rate?

7. - general comments from various Chevron engineers
The Challenge..
“If this stability issue exists, then how come I don’t see this with my platform wells?”
- general comments from various Chevron engineers
Answer: Turns out they are not continuously injecting through the orifice. As these platform wells are completed with a conventional design (unloading valves), the well instability is dampened due to multipointing.

8. Predicting Stability Margins with Transient Programs
OLGA is the primarily tool used within the industry for transient analysis, however it does not look at transient behavior between the surface and downhole injection chokes. DynaLift addresses the gas lift transient issue, but does a poor job of the flowline assessment. Hence, Chevron has to use both programs….
Flowline/ Riser stability OLGA
Gas Lift stability DynaLift

9. Kuito and Benguela-Belize-Tomboco
OFFSHORE ANGOLA:
Kuito and Benguela-Belize-Tomboco

10. Kuito 1A

11. Objectives of Gas lift Study
Determine orifice size that will allow for stable production between MMscfd for the 10 year life of the well
Recommend injection gas rates to minimize erosion and provide approximate time / procedures to unload the well.
How will flowline slugging affect well stability?
- information first presented at the 2000 Offshore Technology Conference, paper #11874

12. Field Parameters for Simulations

13. unstable

14. unstable

15. Simulation: Injection Rate vs Watercut

16. Effect of Fluctuating Wellhead Pressure
unstable

17. U-tube effect

18. THE CHALLENGE …..
“In order to prevent erosion to the orifice, let’s run two of them. Have the upper orifice the “operating point” and then run a REALLY large unloading orifice below it!”
- comments made by the reservoir engineering staff working on the project

19. WHY THIS IDEA WILL NOT WORK ….
LOWER “UNLOADING” ORIFICE
UPPER “OPERATING” ORIFICE
WHY THIS IDEA WILL NOT WORK ….

20. Kuito Update Field start-up Jan 2000 Gas Lift injection began May 2000
Serious Problems with Flowline Stability
Engineering currently working on next 11 producers ….. Completed field testing to calibrate Olga model and the engineers using Olga and Dynalift are working as one “unit”.

23. BENGUELA-BELIZE-TOMBOCO PROPOSED DEVELOPMENT
- ONLY SUBSEA WELLS EXPECTED ARE 2 WATER SOURCE WELLS EACH SUPPLYING 40,000 BWPD

24. BBT team wanted to lift 40,000 bwpd using gas lift

25. EAST COAST CANADA: HEBRON

26. HEBRON ARTIFICIAL LIFT STUDY
DETERMINE METHOD OF LIFT (ESPs or GAS LIFT)
1870 m TVD, 21 API, 50 m3/m3
Emulsions / Hydrates serious issues
Front-End engineering only concerned with horsepower / production relationship …. not stability
Used both static (for emulsions) and transient programs for the gas lift portion.

27. SAMPLE CURVE FROM HEBRON

28. Example: Effect of Wellbore Step Out
For every set of conditions, an optimum and maximum case was done

30. SAMPLE CURVE FOR ALBA

31. EFFECT OF WATERCUT / WELLHEAD PRESSURE FOR ALBA
700 PSI
500 PSI
750 PSI
700 PSI
500 PSI
750 PSI
Pr=3200 psi
Pr=2800 psi 0%
40%
95% 0%
40%
95%

32. EXISTING SUBSEA GAS LIFT COMPLETION THAT CHEVRON DOES NOT RECOMMEND!!
“the name / location has been removed to protect the innocent”
16/64th valve
20/64th valve
28/64th valve
DUMMY VALVE !!
Available gas injection pressure = 1300 psi from 3500 m away
In addition, the “flow conduit” ID goes from 3.5” (gravel pack completion) to 9 5/8” (for 700 m / 2300 ft) to 4.5 (upper completion)

33. Thank You For Listening
Chevron’s World of Artificial Lift
North Sea
(ESP/GL)
Canada
(PCP/GL/BP/ESP)
USA
(PCP/GL/BP/ESP/JP)
Kuwait
(PCP)
China
(ESP/GL)
Thailand
(GL)
That ends my presentation. Once again, I would like to thank the organizers for letting me present today. Now, iIf there is some equipment or method that you did not see here, chances are it did not work for us or we were unable to get it into country. For those vendors in the audience who have a product that you know is applicable and we have not tried it, catch me during the next few days to talk. Now, does anyone have any questions on what was just presented?
Nigeria
(ESP/GL)
Venezuela
(BP/ESP/PCP)
Indonesia
(ESP/BP/PCP/GL)
Colombia
(PCP)
Angola
(GL/PCP/CTESP)
Australia
(GL/BP)
Argentina
(BP/ESP/ GL)