Two methods are presented for predicting critical oil rate for bottomwater coning in anisotropic, homogeneous formations with the well completed from the top of the formation. The first method is based on an analytical solution where Muskat's assumption of uniform flux at the wellbore has been replaced by 'that of an infinitely conductive wellbore. The potential distribution in the oil zone, however, is assumed unperturbed by the water cone. The method is derived from a general solution of the time-dependent diffusivity equation for compressible, single-phase flow in the steady-state limit. We show that very little difference exists between our solution and Muskat's. The deviation from simulation results is caused by the cone influence on potential distribution.The second method is based on a large number of simulation runs with a general numerical reservoir model, with more than 50 critical rates determined. The results are combined in an equation for the isotropic case and in a single diagram for the anisotropic case. The correlation is valid for dimensionless radii between 0.5 and 50 and shows a rapid change in critical rate for values below five. Within the accuracy of numerical modeling results, Wheatley's theory is shown to predict the correct critical rates closely for all well penetrations in the dimensionless radius range from 2 to 50.

This paper reviews reservoir performance and management of the Statfjord field after 8 years of production. The reasons behind the reservoir development strategies and field experiences are presented. The field comprises three reservoirs produced simultaneously with designated wells for each reservoir: the Upper and Lower Brent and the Statfjord. The two Brent reservoirs are produced with a waterflood, while the Statfjord reservoir is produced with a high-pressure miscible gasflood.The original development plans have been refined on the basis of field performance through an extensive monitoring program and use of reservoir simulation. The induced gamma ray spectra (IGRS) log is used to monitor water movement in the Brent reservoirs, while the compensated neutron tool (CNT) is the main tool used to monitor the gas flood in the Statfjord reservoir. The acquired data have improved the geologic model and the knowledge of fluid movements in all three reservoirs. This resulted in a large and complex reservoir simulation model with more than 20,000 gridblocks. Geology and Reservoir DescriptionThe two main Statfjord field oil-producing reservoirs are the deltaic sandstones of the Middle Jurassic Brent group and fluvial sandstones of the Lower Jurassic/Upper Triassic Statfjord formation.The oil accumulations are trapped along the crest of a large tilted fault block. The reservoirs are dipping at angles of 6 to 8° [0.1 to 0.14 rad] in a westerly direction, and the field is bounded on the east by a mitior boundary fault system. Between the structural crest and the boundary fault, the reservoirs are cut by rotational Journal of Petroleum Technology, July 1988 faulting and truncated by erosional events. The accumulations are sealed by Upper Jurassic and Cretaceous shales. Brent Group. The Brent group is subdivided into five formations and is divided into the Upper and Lower Brent reservoirs for reservoir management purposes. Average gross thickness for the Brent is 510 ft [155 m]. From the top, the Upper Brent consists of the Tarbert and Ness formations. The Lower Brent consists of the Etive, Rannoch, and Broom formations (Fig. 2).The Tarbert is a sandstone unit with minor siltstones, shales, coals, and occasional calcareous bands. Vertical communication is good and horizontal permeability is 2 to 3 darcies. The Ness formation is an interbedded sequence of sandstones, shales, and coals. There is restricted communication between the single sand bodies, but generally good permeability (around 1 darcy) within each sand body. The lower shale in the Ness is a fieldwide pressure barrier separating the Upper and Lower Brent reservoirs. The shale is less defined in the north, where it is interbedded with thick sand bodies. The Etive is a generally clean sand with excellent reservoir properties (5 to 6 darcies). Initial oil saturations are in excess of 90 % . The Rannoch formation has abundant mica, calcite-cemented sandstones, and siltstones at its base and grades into cleaner fine-grained sandstones at the top. Reservoir characteris...

COPyrlSIM 1999, OFFSHORE TECHNOLOGY CONFERENCE TM papw was pmpamd for wmontaticm mlrho 0ff8ftoro T9chnciogy Confam$ct hold in Houston. T*1-. 9-9 May. 1999 W-*r w-sakctd for pmccatatlon by tfw OTC~Comrr4ti-folk.uAng rwiaw of htfomdon comtdned In an Awtrad qhmltmd by* author(s). COnt*IIm of ttw p9mr -Pm~I hm* not k.n 19vimmd by the OfMom Tochnok.gy qnd qrc qubjoct 10 cormctlon by m-u*Or10 l%-matmtsl, u pmmtod, doos not rwccssarlly mtkt q y pwitlon C4 rho CJWKWC Tochnofogy COrtf9r9tICa w IKs 0Mc91's. PCIT?IISSiOIIto cow it r98bfcbd to q sbsmct cf not mom mm S00 tmds. Illuotmttons may not b9 copbd. ma *=1 should contain COIWCUWS dmtvlcdg-t of wham qnd by wlmm rhc papw was pr9sal-k9d. AbstractGeological, reservoir and well-technology related challenges have been overcome in the planning and pre-drilling phases of Heidrun and, although additional challenges remain in the future, the field has come rapidly to plateau production, mainly through high-rate gravel packed oil producers from the highest quality and most homogeneous reservoir, the Fangst, An extensive data acquisition program in the pre-drilling phase has laid the groundwork for improved reservoir description of the complex Tilje and Are Formations, which are heterogeneous reservoirs containing barriers to fluid flow and having complex fluid systems. These formations have the potential of contributing large reserves from this giant oil field. Plans are in place for a pilot water flood in these reservoirs and strategies are being evaluated to realize the value of the undeveloped gas reserves and/or use the gas in secondary recovery of oil from Tllje and Are.