7/11-6

General

Well 7/11-6 is located approximately half way between the Mime and the Ula Fields in the North Sea. The primary objective of well 7/11-6 was to test Late Jurassic sandstones. The secondary objective of the well was to test sandstones of Triassic age. The well was planned to reach total depth at 4400 +/- 200 m, approximately 100 m in to the Triassic.

Operations and results

Wildcat well 7/11-6 was spudded with the semi-submersible installation Treasure Seeker on 9 August 1982 and drilled to TD at 4500 m in the Triassic Smith Bank Formation. The well was drilled without incident except some problems with gumbo in the 17 1/2" section. The well was drilled with seawater and high viscosity pills of pre-hydrated bentonite/lime mud down to 670 m, with KCl/Drispac mud from 670 m to 2060 m, with KCl/Drispac mud converting to gel/lignosulphonate mud in the 2060 m to 3970 m section, and with a lignosulphonate mud from 3970 m to TD.

The well encountered a Late Jurassic Ula Formation gross sand interval of 47 m between 4098 and 4145 m. Based on wire line log evaluation net sand was 21.25 m with an average porosity of 15.8%. The Ula Formation rests unconformable on the Triassic Smith Bank Formation, which consists of interbedded sandstones and shales with local siltstones and rare stringers of limestone. Both the Jurassic and Triassic sandstones proved water bearing, but with residual hydrocarbons in the Ula Formation, based on logs. Shows were reported in the interval 4007.5 m to 4038 m in the Late Jurassic hot shale unit, in the Ula Formation, and some meters into the Triassic.

Four cores were taken in the 8 3/8" section. Cores 1 to 3 were cut mainly in the Ula Formation. The lower part of core 3 and all of core 4 were cut in the Triassic Smith Bank Formation. Thirteen RFT pressure tests were attempted in the well over the interval of 4106 to 4204.5 m. From the pressure tests a water gradient of 0.44 psi/ft (1.014 gm/c