Completion and Workover of Horizontal and Extended-Reach Wells in the Statfjord Field
- Kostøl Petter (Statoil A/S) | Knut Østvang (Statoil A/S)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 1995
- Document Type
- Journal Paper
- 211 - 218
- 1995. Society of Petroleum Engineers
- 3.3 Well & Reservoir Surveillance and Monitoring, 5.7.2 Recovery Factors, 2 Well completion, 4.3.4 Scale, 2.4.3 Sand/Solids Control, 2.2.2 Perforating, 2.2.3 Fluid Loss Control, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.11 Drilling Fluids and Materials, 3 Production and Well Operations, 1.6 Drilling Operations, 5.6.1 Open hole/cased hole log analysis, 1.14 Casing and Cementing, 1.2.7 Geosteering / reservoir navigation, 1.6.1 Drilling Operation Management, 5.6.4 Drillstem/Well Testing, 1.10 Drilling Equipment, 1.6.9 Coring, Fishing, 1.12.2 Logging While Drilling, 2.4.5 Gravel pack design & evaluation, 3.3.1 Production Logging, 1.8 Formation Damage
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This paper gives a short introduction to the Statfjord field and background for extended-reach-drilled (ERD) and horizontal wells. We reviewed experiences with completion and workovers of horizontal and ERD wells on Statfjord. Ten horizontal wells with horizontal sections of up to 2150 m and four ERD wells with a horizontal reach of up to 7290 m were completed. Several wells were recompleted, and we performed interventions for logging purposes. We describe the development of the completion and workover techniques since the first horizontal well was drilled in 1990 to April 1994.
The Statfjord field is in the North Sea 200 km northwest of Bergen straddling the Norwegian/U.K. boundary. The field was discovered in 1974 and was put on production in 1979. Statfjord was developed with three large integrated condeep platforms: Statfjord A, B, and C. A plateau production of around 110 to 120 000 std m3/d was reached in 1986 and remained at this level until 1993. The field is currently on declining production. Ultimate recovery is estimated at 585×106 std m3 of oil, which represents a recovery factor of 55%. By April 1994, around 76% of the estimated recoverable reserves was produced.
A total of 113 wells have been drilled; 78 wells are oil producers, 27 are water injectors, and 8 are gas injectors. Five wells are redrills. Production from each well varies from 500 to 7000 std m3/d.
The first ERD well was completed in Jan. 1990, and the first horizontal well was completed in July the same year. A total of four ERD wells were drilled with a maximum horizontal reach of 7290 m (Fig. 1).1 A total of 10 horizontal (>80°) wells were drilled with a maximum horizontal section of around 2150 m (Fig. 2).
The purpose of the ERD wells was to drain the distant reserves in the northern part of the field at minimum cost. The horizontal wells were drilled to drain wedge zones, fault blocks, and low-productivity zones with a minimum number of wells.
We improved the horizontal and ERD completion techniques from drillpipe-conveyed overbalanced tubing-conveyed perforating (TCP) and unloading with coiled tubing (CT) in 1990 to the current techniques with underbalanced CT-conveyed perforating. We optimized the horizontal well profiles for maximum CT reach, and the monobore completion allowed for low-cost, reliable through-tubing recompletions. We achieved significant cost reductions both in completion and workover of these wells since the first completion. The horizontal and ERD wells contributed a daily production of around 16 000 to 17 000 std m3/d and represented a cumulative production volume of around 15×106 std m3.
The Statfjord field consists of three main oil-producing reservoirs (Fig. 3 ) with the Statfjord on the bottom and the lower and upper Brent on top. The Dunlin reservoir in between has not been developed and represents only a small percentage of the recoverable reserves. The field is around 24 km long and 4 km wide and is dipping at an angle of 6 to 8° toward the west.
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