35/11-4

General

Well 35/11-4 was designed to drill at a site located in block 35/11 which is situated on the eastern flank of the Viking Graben and northwest of the Horda Platform. The regional structural generally trends north-south, with some north-northeast components. Planned TD was 3317 m, which was prognosed to be near top Triassic. The primary objective for 35/11-4 was the Middle Jurassic Brent Group. Reservoirs were expected in the Tarbert, Ness, Etive and Oseberg formations. Secondary targets were possible sand development of Sognefjord Formation sand in the Late Jurassic as well as Paleocene sand mounds.

Operations and results

Wildcat well 35/11-4 was spudded with the dynamically positioned semi-submersible installation Yatzy on 18 August 1990 and drilled to TD at 3127 m in the Early Jurassic Statfjord Formation. Yatzy was the first dynamically positioned drilling unit used offshore Norway and 35/11-4 was the rig's first well. This implied significant rig time spent on testing and down time due to failure of first-time equipment. At a depth of 2072 m one decided to sidetrack the well from 1700 m in order obtain cores from the hydrocarbon bearing zones of the Sognefjord formation. This led to a maximum deviation of 5.7 deg at 1765 m. The well was drilled with seawater and viscous pills down to 1009 m and with KCl/polymer mud from 1009 m to TD.

The Lower Eocene consisted of a continuous argillaceous sequence and no reservoir rocks were penetrated. At 1647 m good reservoir quality sandstones were found in the Paleocene Lista Formation but they were not hydrocarbon bearing. Poor shows were observed in limestones of the Cretaceous Shetland Group. A total of four hydrocarbon-bearing zones were discovered in the Jurassic: in the Sognefjord Formation in the original hole and in the Sognefjord, Fensfjord Formations and Brent Group in the sidetrack hole. Mud log shows were recorded in most of the sandstone intervals from 1984 meters to