34/10-35

General

Well 34/10-35 was drilled on the Tjalve Terrace south-east of the Gullfaks South field in the Northern North Sea. The objective was to test the hydrocarbon potential in the Brent Group between the Gullfaks South field and the 34/10-23 Valemon Discovery.

Operations and results

Well 34/10-23 was spudded with the semi-submersible installation Ross Rig on 5 February 1992 and drilled to TD at 4310 m in the Early Jurassic Statfjord Formation. No significant problems were encountered in the operations. The well was drilled water based with sea water and hi-vis pills down to 1083 m, gypsum/polymer mud from 1091 mud from 1091 m to 3783 m, and with Thermopol mud from 3783 m to TD.

The well penetrated Tertiary, Cretaceous and Jurassic rocks. The Middle Jurassic Brent Group was encountered at 3912.5 m, unconformable below the Heather Formation. The Brent Group consisted of Ness Formation only. The underlying Dunlin Group came in with the Drake Formation at 3941.5 m, and the Cook Formation at 3964.5 m. Gas and condensate was proven in the Ness Formation and in the Cook formation down to top Burton Formation at 4048 m. Pressure data clearly indicated no pressure communication between the Ness and Cook Formation reservoirs. No gas-water contacts were established in the well. Oil shows in traces of sandstones (direct and cut fluorescence) were recorded over the interval 2030 m to 2100 m in the Lista and Våle formations and in the interval 2241 m to 2261 m in the Shetland Group. Cut fluorescence was recorded also in shales from the Draupne and Heather formation.

A total of 133.5 m core was cored in 13 cores. Cores 1 to 11 were cut from 3939 m to 4078 m with variable recovery from 33 to 100%.