Summary This paper presents field data and performance analysis for high-rate gravel-packed oil wells in the Gullfaks field. More, than 2 years' worth of production history is available for the earliest gravel-packed wells. From extensive production testing and reservoir monitoring, the initial performance and performance history before water breakthrough was evaluated. An addendum reviewing later developments (1991–1993) is also included. Introduction The Gullfaks field, operated by Statoil A/S, is in the central part of the East Shetland basin in the northern North Sea, 175 km northwest of Bergen, Norway. Developed with three Condeep(TM) platforms (Gullfaks A, B, and C) the field started production in Dec. 1986. Of a total of 102 planned wells, 56 were drilled as of June 1991; six are subsea satellite wells. Estimated production life of the field is 20 years. The main drive mechanism is water injection. Predicted ultimate oil production from the field is 230 × 10(6) Sm3. The oil is located within three major sandstone units, the Brent Group, the Cook formation, and the Statfjord formation. The lower Brent delta sequence comprises the Broom, Rannoch, Etive, and Ness formations; the Upper Brent consists of the Tarbert formation. The reservoirs are overpressured, with an initial reservoir pressure of 31 MPa at datum depth (1850 m below mean sea level], and a temperature of 70 degrees C. The shallow, highly porous sands generally are poorly consolidated. The oil is undersaturated, with a saturation pressure of approximately 24 500 kPa, depending on depth and location. The oil viscosity is between 1.0 and 1.2 mPa.s at initial pressure conditions. Average horizontal formation permeability in gravel-packed wells varies from 250 to 10 000 md on the basis of transient well-test analysis. Porosity is high, generally between 35 and 40 porosity units. The Gullfaks field is divided into a number of fault blocks and is classified as a complex North Sea reservoir. During the first years of reservoir development, wells were naturally completed and selectively perforated in the relatively strong Rannoch formation. Considerable research was conducted to avoid sand production. After 2 years, development of the overlying weaker Ness and Tarbert formations began. Concurrently, a number of Rannoch wells were constrained by sand production initiated by water breakthrough. In these wells, water breakthrough severely reduced the maximum sand-free rate. Therefore, the need for sand control has increased with time. As a result, 2 years after production started, the completion strategy was changed to gravel packing. By June 1991, 14 platform oil producers were cased-hole gravel-packed. Earlier publications on high-rate gravel-packed oil wells discuss rates of up to 750 Sm3/d. The maximum oil rate produced through a single Gullfaks gravel pack is 5000 Sm3/d, limited only by calculated erosion velocity in the tubing. Gullfaks gravel-packed wells have been production-tested extensively, and laboratory work has been performed for better understanding of gravel-pack performance. This paper presents field data and its evaluation as of June 1991.
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