2/1-7

General

Wildcat well 2/1-7 was drilled on a structure in the centre of the block. The primary target was Rothliegendes sandstone in a large fault bounded structure mapped at base Zechstein Group level. A secondary objective was Late Jurassic Ula Formation sandstone in an extension of the 2/1-3 Gyda discovery. In the 2/1-3 well two sequences of Ula Formation sandstone had been encountered, and the upper of the two had been oil-bearing

Operations and results

Wildcat well 2/1-7 was spudded with the 3-leg jack installation Glomar Moray Firth 1 on 6 September 1984 and drilled to TD at 5464 m in the Permian Rotliegendes Group. Pumping lost circulation material, without changing the mud weight, stopped loss of mud at 1710 m. Top chalk came in at 3190 m. This whole sequence was drilled with turbine. At 3746 m the drill string got stuck, and the tight interval was located between 2600-2900 m. The string was freed by circulating acidic mud. Full circulation was maintained during this whole operation. While pulling out to change bit at 5077 m the drill string was lost in the hole. At the same time 170 bbls of mud was lost. One reason for this mud loss could be the "piston effect" caused by the drill string falling down the hole. The pipe was fished out piece by piece, and the stabilisers above the bit were milled out. At 5081 m the drill string was screwed off 300 m above the bit. Fishing was successful and drilling continued. Drilling was stopped at 5113 a to perform pressure test. During this operation, before reliable results were obtained, the RFT-tool got stuck in the hole. After extensive fishing the operator decided to plug back and sidetrack the hole. The technical sidetrack was kicked off at 5092 m, and drilled to 5119 m. Problems at this depth made another sidetrack necessary, and the hole was plugged back to 4747 m. The new sidetrack was kicked off from 5080 m and dri1led to a TD of 5464 m, which made this hole 4 m short of being th