30/9-1

General

Well 30/9-1 was drilled on the southeast part of the Oseberg fault block (Alpha structure) in the North Sea. The Alpha structure is an eastward tilted fault block that contains proven reserves of oil and gas in the Middle Jurassic Brent Group sandstone reservoir. The primary objective of the well was to establish the oil/water contact in this part of the structure. The well was planned to be drilled to a total depth of 2850 m, approximately 100 m into the Dunlin Group.

Operations and results

Appraisal well 30/9-1 was spudded with the semi-submersible installation Treasure Seeker on 24 October 1982 and drilled to TD at 2895 m in the Early Jurassic Drake Formation. No significant problem was encountered in the operations. The well was drilled with seawater/hi-vis pills and pre-hydrated bentonite down to 969 m, with KCl/Drispac mud from 969 m to 2515 m, and with KCl/polysal mud from 2515 m to TD.

The Brent Group was found hydrocarbon bearing from 2685 m down to 2738 m where the free water level was established. This interval comprises the whole of the Ness Formation and the uppermost 3 m of the Etive Formation. Net pay in the interval was 10.5 m. Poor oil shows were recorded on limestone cuttings in the interval 2281 to 2232 m in the uppermost Shetland Group. Good oil shows were recorded through the oil column of the reservoir. Below the contact at 2738 m, shows became weaker and patchy down to 2778 m. Below this depth only some weak shows on claystone from three sidewall cores in the interval 2872 m to 2895 m were reported.

Seven conventional cores were cut from 2682 m at the top of the Ness formation to 2784.9 m, into the Dunlin Group shales. RFT fluid samples were ta