25/2-12 A

General

Well 25/2-12 was designed to drill the crest of a NNE-SSW trending westward tilting Jurassic fault block. The northern extension of this structure was drilled in 1975 by well 25/2-4 in a down dip position to well 25/2-12. A 70 m hydrocarbon bearing column was encountered in the Vestland Group. The Statfjord Formation was found water bearing. The main objectives of well 25/2-12 were to appraise and test the hydrocarbon discovery of the Middle Jurassic Vestland Group and to explore the Statfjord Formation up dip from well 25/2-4. Due to an unprognosed fault top Vestland came in 112 m deeper than prognosed in 25/2-12. Hence, side track 25/2-12 A was decided. The main purpose of the sidetrack was to explore the still untested Vestland up dip to the West.

Operations

Appraisal well 25/2-12 A was sidetracked from 3099 m in well 25/12-2 on 17 November 1988 by the semi-submersible rig West Vanguard and drilled to TD at 3865 m in the Middle Jurassic Vestland Group. During drilling the string got stuck at 3692 m. Drilling was stopped at 3714 m, one metre above the Vestland reservoir. Fishing was unsuccessful, and the string was cut at 3485 m. When tripping out the well started to flow. Several days were needed to control the well and finally a cement plug was set from bottom to 3528 m. The cement was dressed to 3612 m and a 7" liner was set from 3600 m to 2927.5 m. After that the cement was drilled out to 3612 m before commencing to drill the 5 7/8" section. During drilling the 5 7/8" phase the string got stuck several times, and finally stuck at 3865 m. While jarring the well started flowing again. After controlling the well a 4 1/2" liner was set from 3863 m to 3562 m. Cement was drilled out to 3830 m before logging. Due to the problems no open hole logs were run in well 25/2-12 A; all logs were run behind casing and no fluid samples were taken. No cores were cut. The sidetracked well 25/2-12 A was completed 6 April 1989 a