7/12-5

General

Well 7/12-5 was drilled ca 4 km northwest of the Ula Field in the North Sea. The objective was to test the hydrocarbon potential in Late Jurassic Sandstones. Secondary objectives were Early Jurassic and Triassic sandstones.

Operations and results

Wildcat well 7/12-5 was spudded with the semi-submersible installation Borgsten Dolphin 6 February 1981 and drilled to TD at 4440 m in the Late Permian Zechstein Group. There were some problems with drilling the section from 2851 to 3741 m due to junk in hole, otherwise operations proceeded without significant problems. The well was drilled with sea water and hi-vis pills and gel down to 467 m and with gypsum/lignosulphonate/CMC mud from 467 m to TD.

The Mandal Formation was penetrated at 3731 m, while the Farsund Formation was penetrated at 3763 m. The Ula Formation was penetrated at 3831 m and consisted of a 69.5 m thick homogenous sandstone, very fine to fine grained with poor reservoir characteristics (porosities from 7 to 14 % and permeabilities from 0.3 to 3 mD). All attempts to obtain reservoir pressures and fluid samples failed due to tight formation. Oil shows were recorded in the upper half of the reservoir and an oil water contact was established at 3872. Log analysis indicated that no significant hydrocarbons were present below the Ula formation where all porous zones calculated high water saturations. Weak shows were recorded in sandstone in the interval 3940 to 3960 m in the Skagerrak Formation. Weak shows were recorded also in siltstone in an isolated sample from 2235 m in the Hordaland Group.

Four cores were cut from 3844.5 to 3912.15 m in the Ula, Fjerritslev, and Skagerrak formations. Core depths are 4.8 m deeper