Subsea Smart Multilateral Wells Increases Reserves at Gullfaks South Statfjord
- Vibeke Eilen Jensen Haugen (Statoil) | Ann-Kristin Fagerbakke (Statoil ASA) | Bianc Samsonsen (Statoil) | Per Kr. Krogh (Statoil)
- Document ID
- Society of Petroleum Engineers
- SPE/DOE Symposium on Improved Oil Recovery, 22-26 April, Tulsa, Oklahoma, USA
- Publication Date
- Document Type
- Conference Paper
- 2006. Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 2.2.2 Perforating, 5.1.5 Geologic Modeling, 2 Well Completion, 1.10 Drilling Equipment, 2.4.3 Sand/Solids Control, 2.3 Completion Monitoring Systems/Intelligent Wells, 1.14 Casing and Cementing, 5.7 Reserves Evaluation, 4.1.2 Separation and Treating, 5.7.2 Recovery Factors, 5.1.2 Faults and Fracture Characterisation, 1.6.2 Technical Limit Drilling, 3.3.1 Production Logging, 2.3.3 Flow Control Equipment, 4.1.5 Processing Equipment, 1.6 Drilling Operations
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The Statfjord Formation in Gullfaks South was discovered in 1978, and came on production in 1999 as part of the Gullfaks Satellite Development.
In the Plan for Development and Operations (PDO) The STOOIP was estimated at 35 million Sm3, with estimated recoverable reserves of 12.6 million Sm3. Start up of the first two wells in 1999 showed that the production rate was lower than expected, most likely as a result of poor reservoir communication. A third well was drilled in 2001 and experienced gas breakthrough shortly after startup. Based on these observations booked reserves were reduced to 2.4 million Sm3 in the reservoir management plan for 2002.
Production has been limited by low connectivity, reservoir heterogeneity and gas breakthrough. Surface operated downhole inflow control and multilateral wells have been identified as solutions to these limitations, which has lead to an increase in expected oil recovery.
This paper describes the process of implementing Downhole Instrumentation and Control System (DIACS) and Multilateral Technology (MLT) in three horizontal subsea wells drilled in 2003 and 2004. This has led to a twofold increase in the reserve estimate to 5.4 million Sm3 in the reservoir management plan for 2005.
Gullfaks South (GFS), operated by Statoil ASA, is located in Block 34/10 of the Norwegian sector of the North Sea, approximately 150 kilometers North-West of Bergen. The field is a subsea satellite tied back to the Gullfaks A and C platforms and consists of two reservoirs units, the Brent and Statfjord Formations, which are independently developed. Production from the Statfjord Formation (Figure 1), which started in 1999, is routed to Gullfaks A.
The Statfjord Formation in GFS is structurally complex with numerous fault segments and indications of locally varying fluid contacts (Figure 2). The formation is approximately 300 meters thick and exhibits a transition from continental, lower alluvial plain and fluvial deposits, with estimated high connectivity, to shallow marine sediments. Production experience has, however, shown that there is less connectivity than expected. The initial reservoir pressure, at 3300 m TVD MSL, was 476 bars and the temperature 128°C.
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