7/9-1

General

Well 7/9-1 is located on the Reke Fault Zone between the Jæren High and the Sørvestlandet High. The objective of the well was to test for hydrocarbons in Tertiary, Cretaceous, Jurassic, and Triassic reservoirs over a Zechstein salt well which showed 1300 feet of vertical closure over an area of about 65 square km at the base Tertiary level.

The well is Reference Well for the Gassum and Fjerritslev formations.

Operations and results

Wildcat well 7/9-1 was spudded with the jack-up installation Mærsk Explorer on 22 April 1970 and drilled to TD at 2931 m in Zechstein salt. The well was spudded using a high viscosity gel-seawater mud. After drilling out of the 20" casing, which stuck at 242 m, the mud was converted to a lignosulphonate-seawater. The 213 m of 26" rat hole left below the 20" casing gave considerable trouble by acting as a build up area for large balls of gumbo, which collected there as 17 1/2" hole was being made. An attempt to run electric logs at the 13 3/8" casing point failed because of the fill at 442 m. Drilling detergent was used to reduce torque and drag and was successful in the upper part of the hole. The diesel oil content of the mud was maintained between 4% and 7%. A deviation problem arose in the 8 1/2" hole, starting around 2255 m where the angle was 4.5°. It increased steadily and at 2723 m the last survey point was 5.5°. Light bit weight, high rotary speeds, and a bottom hole assembly usually successful in dropping angle had no effect.

The Tertiary Paleocene Sands were not developed over the structure. The other objectives, the Tertiary Danian calceranites, the late Cretaceous Maastrichtian chalk, and the Middle Jurassic to Triassic sandstones, were confirmed, but were water bearing. During the drilling of the Tertiary section to a depth of 1676 m shale gas from the sometimes richly organic shales maintained a high background between 0.5% and 1% methane in