Painting the pores

1. Painting the pores Gullfaks Diverging Pilot Well A-35 Author: Rune Instefjord,

2. Outline • Introduction to the Chemicals. • How does the chemicals work. • Planning of pilot on Gullfaks • Selection of pilot area • Simulation • Implementation • Summing up

3. Abiogel coat Introduction to Abio gel • Abio gel is compound, consisting primarily of Sodium silicate. When Abio gel is brought into contact with divalent cations (i.e. Ca and Mg) in formation- or seawater it reacts to form a microcrystalline suspension which may become a stiff gel if concentration of divalent cations exceeds about 1 %. Otherwise it behaves as a cement paint coating the rock matrix. The following text and illustration is provided by CNPC • narrow the flow channels gradually • keep certain permeability • in favor of indepth fluid diversion Abiogel is actually a gel used in chromatography and is also a brand name for cement paint

4. Gullfaks flow diversion project • 1000 ton chemicals (silica based) injected into the injector A-35. • The chemicals is environmental classified as yellow. It is environmentally acceptable and unproblematic to use. • The chemicals shall move into the reservoir and form micro gel particles, which will stick to the surface of the pores and thereby reducing the permeability in invaded zones. • The water will be forced to find new paths and invade less water flooded areas. • Hit bypassed oil and increase the oil recovery. Bypassed oil

5. 5 Illustration of water diverging • Important issues: • Improve the volumetric sweep efficiency. • Reduce permeability and reduce flow of water in existing water channels. Divert water into unswept areas. • Alternative to drilling of new wells into areas with very uncertain flooding pattern.

6. Illustration of water diverging 6

7. layer42 layer36 layer38 layer40 layer44 layer46 layer48 layer49 Remaining Oil Distribution • Plane remaining oil mainly distributes out of the main water streamline region and in the bottom low permeability formations

8. Russia Iceland Finland Gullfaks Norway Sweden North Sea Denmark UK Ireland Germany Introduction to Gullfaks • Discovered: 1978 • Start production: 1986 • STOOIP: 599 MSm³ • Base oil reserves: 365 MSm3 • Produced to date: 351 MSm3 • Recovery of base reserve: 96% • Overall expected recovery: 61% • Overall recovery pr. 2011: 59% • Current daily production: 14 kSm3 • Current average water cut: 84 % • Initial pressure/temperature: 310-320 bar/ 71 oC at 1850m TVD MSL • Bubble point pressure: ~200-240 bar at 1850m TVD MSL • GOR: ~ 100 Sm³/Sm³ • Oil viscosity: ~ 0.5 – 1 cp

9. Segment selected for a water based chemical method. STOOIP in lower Brent is 20,3 MSm³ oil. Lower Brent in H1 has ”only” 57 % recovery factor. Potential 2 - 5 MSm³ mobile oil left. Relatively isolated segment. A lot of data is collected in this area. It was the first production area and therefore a lot of good, initial data. 2 active wells in lower Brent, A-35 (injector) and A-39A (producer). 2 active producers in upper Brent, B-37 and A-38A. Pressure communication between B-37 and lower Brent. No communication with A-38A? Problem with H2S in A-39A. B-37 may also give a H2S problem. 9 Pilot area: Lower Brent, segment H1

10. Simulation • Establish a History Matched (HM) simulation model for the H1-segment • Understand the mechanism of the chemicals and find the relevant parameters • Make predictions using the optimal simulation tool and – method using restart from the HM model One-dimensional model to simulate sand pack experiment Parameter adjustment

11. Operation, offshore setup Scandi Flora at the North Shaft (NS) Hose hanger @ BOP deck NS Connection to Chicksan 2” line KillWing Valve @ WellHead

12. Events each batch Mixing chemicals at CCB, Ågotnes outside Bergen. 15-20 % wt. solution mixed in Fresh Water. Mixed max 800 m³ of solution due to regulations by the government. Scandi Flora transported and pumped the chemicals into A-35. Start injection 17.09. 100 m³ KCl preflush and postflush, rate: 1 000 m³/d in the 2 first batches. Injected 150 - 800 m³ solution with chemicals at rate: 1 000 - 2000 m³/d. Density of the liquid was 1.23. Viscosity around 3.5 cP. PH around 13. End injection 06.11. Restrictions on wave height. Maximum 3 m due to hook up between vessel and platform.

13. Batch 1 Before 1st Batch treatment DHP for inj. rate 2000 sm3/d was 296bara, after treatment DHP stabilized around 280bara. This effect was interpreted as stimulation of the well.

14. Pressure details batch 1 Start SW injection Start chemical injection End chemical injection Start KCl postflush Stop KCl preflush Start KCl preflush

15. Pressure 4th batch (part 1) Well shut in Increase due to density Drop due to density Start SW injection Start chemical injection

16. SW inj. pressure after each batch

17. Summary • Successful operation but used some more time than planned due to weather conditions. • It is to early to see any IOR in the producers, so we do not know the answer on the questions! • We expect increased oil production in the producers after around 1 year. • Have technical problems in one of the wells per today and the well are therefore shut in. This may worsen the interpretation of the pilot. • First multi well diverging project in the North Sea. If success it may give a lot of increased oil for more fields than only Gullfaks.

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