The need to simulate advanced wells (horizontal and multilateral wells and smart's wells containing flow control devices) requires a correspondingly sophisticated type of well model to be implemented in reservoir simulators. The model must be able to determine the local flowing conditions (the flow rate of each fluid and the pressure) throughout the well, and to allow for pressure losses along the wellbore and across any flow control devices. This paper describes an advanced well model in which the wellbore is divided into an arbitrary number of segments. The well model has been implemented in a black-oil reservoir simulator, and the paper describes two case studies which assess the performance of the model and use it to examine the effects of flow control devices on two types of well. P. 171

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...