35/11-1

General

Wildcat well 35/11-1 was drilled on the "A" structure close to the border between Block 35/11 and Block 35/12, and ca 25 km north of the Troll Field. Its primary objective was to assess the hydrocarbon potential in Middle to Upper Jurassic strata on the "A" structure that straddles the border between Block 35/11 and the unlicensed Block 35/12. Sands of Lower Jurassic age were regarded as secondary objectives. Planned TD was into the Triassic.

Operations and results

A total of 317 pockmarks were identified in the area from the site survey. The average density was estimated to 20 per square kilometre. The average depth of these was 1-2 m, though some were of greater depth. None of the pockmarks were seen to be active.

Wildcat well 35/11-1 was spudded with the semi-submersible installation on 23 May 1984 and drilled to TD at 3361 m, approximately 100 meters into in the Triassic Hegre Group. The 36" hole section was drilled through boulder beds causing the bit to build angle. Because of high deviation the well was re-spudded. After drilling the 26" hole, the well flowed several times. Although the well would not stay static, it was decided to run the 20" casing in an attempt to seal off the water flow. This resulted in the 20" casing parting at the wellhead, but was successfully recovered. After reaming some tight spots the 20" casing was set and cement was squeezed to seabed to stop the water flow in annulus. Some tight spots were experienced in the 17 1/2" and 12 1/4" hole sections. Lost circulation occurred at 2439 m, due to this the 9 5/8" casing was run. The well was drilled with gelled seawater spotted with hi-vis pills down to 1015 m and with KCl/polymer mud fr