35/11-6

General

Block 35/11 is located on the northwestern edge of the Horda Platform, on the Lomre and Uer Terrace. The Northern part of the Viking Graben is immediately to the Northwest. The block lies due north of the Troll Field. The well was drilled to appraise the 35/11-2 Discovery, which proved oil and gas in the Middle Jurassic and had shows in Late Jurassic Intra Heather Sandstones. The primary objective was to evaluate the Middle Jurassic sandstones of the Brent Group, and the location was chosen such that the OWC of the Tarbert Formation could be identified. The secondary objective was the Late Jurassic Intra Heather Sandstones, which were thought to be much thicker than in the 35/11-2 location.

Operations and results

Wildcat well 35/11-6 was spudded with the semi-submersible installation Sovereign Explorer on 30 January 1992 and drilled to TD at 3990 m in the Early Jurassic Statfjord Formation. The well was drilled with seawater and viscous pills to 985 m and with KCl/polymer mud from 985 m to TD. In the Late Jurassic, sandstones were found in the Upper Heather and Sognefjord Formations. In the Upper Heather Formation a very porous and permeable sandstone contained 1.2 m of oil. A core was taken at the base of this interval and an RFT sample at 3072.7 m recovered gas and heavy oil. RFT pressure and sampling data indicated that the zone had excellent permeability in places. The pressure data did not support communication with 35/11-2, and a large sampling pressure draw down indicated a limited accumulation. The sandstone in the Sognefjord Formation, although thicker, was much less porous and contained only traces of residual oil. Two cores were taken in this Formation and an RFT at 3174.5 m recovered only traces of hydrocarbons. In the Middle Jurassic Brent Group, shows were observed in cores but these were probably residual as petrophysical results showed only low oil saturations. The reservoir quality of the sandstones was generally p