2/1-6

General

Well 2/1-6 is located on the northern side of the Gyda structure on the Cod Terrace in the North Sea. The main target was the Late Jurassic Sandstone, informally called the Gyda sandstone member. The well was located such that it should prove the oil water contact of the 2/1-3 oil discovery, and by this establish whether 2/1-3, 2/1-4 and 1/3-3 all have encountered the same oil accumulation on the two sides of the saddle point. It should also test further the extent and the quality of this Upper Jurassic reservoir.

Operations and results

Appraisal well 2/1-6 was spudded with the semi-submersible installation Dyvi Alpha on 30 April 1984 and drilled to TD at 4583 m (4588 m loggers depth), one metre into Late Triassic sediments of the Skagerrak Formation. The well was drilled with seawater and pre-hydrated bentonite spud mud down to 635 m, with KCl/polymer mud from 635 m to 3424 m, with lignosulfonate mud from 3424 m to 4124 m, and with high temperature polymer mud from 4124 m to TD.

The Gyda sandstone member was penetrated at 4173 m logger's depth. The reservoir is 205 metres thick, generally very fine to fine grained sandstone, but with a 28 metre thick siltstone incorporated in the uppermost part. Reservoir properties were very variable. Reasonable reservoir properties were found near the top of the reservoir. They were poor in an upper siltstone zone, in an intermediate 77 metre thick quartz overgrowth zone and at the base of the 2/1-3 sand where it shaled out into the Farsund Formation. Shows were recorded from 4174 to 4178 m in a sandstone that had very low permeability, and could not be tested. Minor patchily developed shows were observed from 4178 down to 4203 m, all within