Successful Time Lapse Studies on the Gullfaks Field, North Sea—Statoil
Gullfaks is a large tilted fault-block reservoir on the western margin of the North Viking Graben in the Norwegian North Sea, discovered in 1979, and with remaining reserves of some 120million cm. of oil. The recovery factor is around 53%. Production is from Brent, Cook, and Statfjord Jurassic sandstone units, with the top at about 1800m depth. The major fault throws are up to 300m in the north-south direction, and there are smaller east-west faults which could further compartmentalise the reservoir.
It has been surveyed by four 3-D seismic surveys, in 1979, 1985, 1995, and 1996. Platforms were moved into place shortly after the 1985 survey, and production commenced in December 1986. The oil-water contact has moved upwards by about 50m since start of production, and is rising at about 13m per year.
Gullfaks supplies some 20% of Norway's production, delivering 585,000 bbl/day. Production peaked in 1994. There are 102 production wells, and 127 water injection wells.
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“This book, prepared for use with the first SEG / EAGE Distinguished Instructor Short Course, discusses Â"time-lapse seismicÂ" and enables geoscientists to assess the value and risk of this new technology. It covers the rationale and driving forces behind time-lapse seismic by examining the limitations of existing methods of tracking fluid flow between wells. It examines those reservoir properties that change with time and what can be observed on seismic data over elapsed time. The repeatability of seismic data and the use of Â"legacyÂ" data sets are discussed, along with a review of the seismic data acquisition schemes and data processing requirements for time-lapse analysis. The rock-physics foundation for data analysis and interpretation options also are described. A selection of industry case histories illustrates many of these points. The reader will gain an understanding of key success factors, key calibration requirements, and key uncertainties of time-lapse seismic in reservoir management.”