30/9-4 S

General

Well 30/9-4 S was drilled on the B-structure on the southeast flank of the Oseberg Field in the North Sea. The structure is an elongated rotated fault block bounded by faults in all directions. The Brent Group is truncated by the Base Cretaceous unconformity, and this well was expected to go directly from Cretaceous to the Ness formation. The objectives of the well were to find hydrocarbon accumulations in the Brent Group, secondary in the Statfjord Group. The well was designed to penetrate the Brent Group in a position where the sand in the Ness Formation is preserved. The well was deviated westwards at an angle of approxi­mately 40°.

Operations and results

Wildcat well 30/9-4 S was spudded with the semi-submersible installation Treasure Seeker on 22 November 1984 and drilled to TD at 4303 m (3577 m TVD) in the Early Jurassic Eiriksson Formation. No significant problems were encountered during operations. The well was drilled with spud mud down to 222 m, with seawater/gel from 222 m to 630 m, with oil based Safemul mud from 630 m to 3297 m, with NaCl/polymer mud from 3297 m to 3680 m, and with oil based Safemul mud from 3680 m to TD.

The well 30/9-4 encountered two separate hydrocarbon reservoirs in the Middle Jurassic Brent Group. Pressure data indicated no communication between the two hydrocarbon columns. The Tarbert Formation and uppermost Ness Formation (3295-3379 m, 2773-2841 m TVD) sandstones were found to be gas bearing, but no definite gas/fluid contacts were evident. Net pay in the gas zone was calculated to be 27.6 m (22.1 m TVD), average porosity 18.6%, and the average water saturation 20.9%. The Ness Formation (3379-3551 m, 2841-2979 m TVD) proved to be oil bearing, but again no OWC could be discerned. Net pay