31/4-2

General

Well 31/4-2 is a replacement for junk well 31/4-1. The well is located on the Brage Horst between the Oseberg and Troll Fields in the Northern North Sea. The primary objective was Middle Jurassic sandstones of the Brent Formation. A "flat-spot" was seen on the seismic sections and tentatively interpreted to represent a gas fluid contact in these sandstones. A secondary objective was sandstones in the Early Jurassic Statfjord Formation. Sandstone intervals of upper Early Jurassic age (Dunlin Formation) and of Triassic age (Hegre Group), were also expected to be penetrated, but were not considered to be prospective. The well was planned to be drilled to a depth of 2930 m RKB (+/- 90 m), ca 100 m into the Triassic.

Operations and results

Wildcat well 31/4-2 was spudded with the semi-submersible installation Norskald on 26 September 1979 and drilled to TD at 2900 m in the Triassic Lunde Formation. There were some problems with keeping position and anchor movements in rough weather, but otherwise operations went forth without significant problems. The well was drilled with Seawater and pre-hydrated bentonite down to 990 m, with Seawater/Drispac/pre-hydrated bentonite from 990 m to 1712 m, and with seawater/prehydrated bentonite/ligcon/Unical mud from 1712 m to TD.

Good oil shows were recorded on sidewall cores from thin sandstone stringers at 2061 to 2069 m in the upper part of the Shetland Group. The well penetrated top Draupne Formation at 2146 m and top Heather Formation at 2171 m. The Heather Formation contained a 49 m thick very fine to silty water-bearing sandstone interval from 2190 to 2239 m. The well penetrated two hydrocarbon bearing sandstone intervals at 2325 to 2329 m and 2344.5 to 2354 m within a 29 m thick Mi