Oseberg Field

ABSTRACT The Oseberg field is located in the Norwegian North Sea in blocks 30/6 and 30/9, approximately 140 km northwest of Bergen, Norway. The field came onstream in December 1988. The Oseberg field comprises three major eastward-tilted fault blocks called Alpha, Gamma, and Alpha North. The hydrocarbons are contained in the sandstones of the deltaic Middle Jurassic Brent Group. The Brent Group exhibits excellent reservoir properties, including porosities from 20 to 25% and permeabilities ranging up to several darcys. The gross thickness of Brent ranges mainly between 50 and 190 m (Table 1). The maximum extension of the field is 26 km, and the maximum width is about 6 km. The structural dip is normally 6 to 10° east-northeast. Gas caps are present in all structures. The Alpha structure has a vertical gas column of 380 m and an oil column of 210 m, for a total hydrocarbon column of about 600 m. Reservoir engineering studies have shown that a greater ultimate volume of oil can be recovered by gas flooding than by water-flooding. Consequently, pressure maintenance by gas injection has been chosen as the production mechanism for the Alpha and Gamma structures. An adequate supply of gas for injection can be obtained only by importation of large quantities from the huge Troll field by means of a 48-km-long pipeline. The Alpha North structure will be produced mainly by water flooding. On the Oseberg field itself, the development comprises a field center in the southern part of the field (onstream), a production platform in the northern part (in construction), and three subsea wells. The current estimates of field reserves are 231.6 million standard m 3of oil and 92 billion standard m 3of gas.