33/12-5

General

Well 33/12-5 was drilled on the Tampen Spur in the northern North Sea. It was drilled on the southeast, downfaulted flank of the Statfjord structure, but on the upthrown block of the major, east-bounding Statfjord fault. The well was programmed to test in a higher structural position, a Triassic sand, found water bearing in the 33/12-2 well, and to evaluate older, untested section beneath the sand. The Triassic sand in 33/12-2, defined seismically by the "R2" horizon, had been tentatively identified as Early Triassic. Secondary objectives were possible Jurassic reservoirs preserved within this downfaulted area east of the Statfjord Field. The 33/12-4 well was a similar test on the east flank of the Statfjord feature. This well found a thin Jurassic/Upper Triassic? sand with good porosity, which tested saltwater with minor amounts of oil.

The well is type well for the Lomvi and Teist formations.

Operations and results

Appraisal well 33/12-5 was spudded with the semi-submersible installation Norskald on 9 October 1975 and drilled to TD at 4574 m in the Triassic Lomvi Formation. The well was drilled water based with a lignosulphonate mud from 485 m to TD.

The Tertiary and Late Cretaceous sections were similar to other wells in the area, consisting predominantly of claystones and siltstones with minor sands. Along the southeast flank of the Statfjord feature, erosion appears to have removed Jurassic sediments and a portion of the Upper Triassic prior to draping of an indeterminate Jurassic sand, interpreted as reworked Statfjord Formation sand, on the eroded Triassic surface. Only minor shows were encountered in the reworked Jurassic sand, which tested saltwater on DS