2/8-11

General

Well 2/8-11 was drilled as a field delineation well intended to help establish the commerciality of the southern North Sea Valhall Field, which was discovered by well 2/8-6 and confirmed by wells 2/8-8, 2/8-9 and 2/8-10. The primary objective was to test the Late Cretaceous chalk reservoirs and to estimate the presence of hydrocarbons.

Operations and results

Appraisal well 2/8-11was spudded with the semi-submersible installation Ross Rig on 10 August 1976 and drilled to TD at 2655 m in the Early Cretaceous Rødby Formation. The well was drilled in a total of 33 days without any major drilling problems. However, 13 days were spend on logging in the 12 1/4-inch hole and setting and cementing two completion strings comprising of a 7-inch liner cemented inside the 9 5/8-inch casing. The well was drilled with seawater/bentonite/caustic soda down to 381 m, with Drispac/Dextrid/lignosulphonate mud from 381 m to 1294 m, and with Drispac/Dextrid/lignosulphonate/Soltex mud from 1294 m to TD.

The well penetrated a normal Quarternary-Tertiary sequence with the top Paleocene Ash Marker at 2437 m, 51m lower than predicted. The Late Cretaceous Maastrichtian chalk (Tor Formation) was encountered at 2468 m with a total thickness of 15 m and with an oil column of the same magnitude. The porosity was 40-50% and the water saturation close to zero. The two Coniacian-Turonian reservoirs, (upper and lower Hod Formation) had porosities of 30-40% and water saturations averaging 50% with 18.5 m pay in the upper reservoir and 33.5 m pay in the lower reservoir. The Turonian shale was penetrated at 2612 m and the top of the Early Cretaceous was reached at 2624 m giving a total chalk thickness of 144 m.