Reservoir Geology of Draugen Field, Offshore Norway

M. J. B. G. Goesten

The Draugen field in the Haltenbanken area on the mid-Norwegian shelf was discovered by Norske Shell in 1984 when the exploration well 6407/9-1 encountered oil in a previously unknown Upper Jurassic sand. Five further appraisal wells were drilled between 1984 and early 1986 and a development plan was finalized during 1987. The low-relief anticlinal structure, with a vertical closure of 45 m, has an areal extent of 20 by 6 km and contains approximately 1,000 million standard bbl of undersaturated oil.

The reservoir comprises a high-quality coarsening-upward sand sequence interpreted as a single offshore sandbar encased in marine shales. It was recognized early in the appraisal phase that the reservoir sands could be of limited lateral extent. Detailed sedimentologic studies combined with high-quality seismic data, enabled the optimization of appraisal well locations and subsequent delineation of sandbar geometry. Thus, with a limited number of relatively widely spaced wells, a reservoir geologic model was developed as a basis for numerical simulation.

The sandbar development is generally confined to within the areal closure and the reservoir is separated from the main aquifer by a 2-30 m thick shale. Fault offsets may, however, provide localized communication paths. Intraformational shales are notably absent, and vertical and lateral communication within the hydrostatically pressured reservoir are believed to be excellent. In view of the low intrinsic reservoir energy, the development will involve pressure support from water injection with oil offtake via crestal producers.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.