2/7-28

General

Exploration well 2/7-28 was drilled on the Eldfisk Jurassic Prospect, on the flank of the Eldfisk Field on the western side of the Feda Graben in the North Sea. The well was positioned 1.8 kilometres west of the Eldfisk Alpha Platform. The primary objective was to prove hydrocarbons in sandstones in the Late Jurassic Eldfisk Formation. The Eldfisk Formation is interpreted as high density turbidite/debris flow deposits located on the eastern side of the major northwest-southeast trending Skrubbe Fault.

Operations and results

Well 2/7-28 was spudded with the jack-up installation Mærsk Guardian on March 8, 1992 and drilled to TD at 3893 m, 54 m into the Late Permian Zechstein Group. Drilling to the Upper Palaeocene Section proceeded without major difficulty, but the 11 3/4" liner was set higher than prognosed because of a combination of lost circulation in the Lower Palaeocene Våle Formation and instability in the Tertiary section above. A prognosed depleted chalk reservoir horizon, the flank of the Eldfisk Field, necessitated setting 9 7/8" casing at top of the Ekofisk Formation. Drilling proceeded to 3050.4 m in the Lower part of the Hod Formation, the proposed setting for the 8 3/4" casing. While under-reaming before running the linear, an under-reamer arm was lost in the hole. A successfully sidetrack hole was made below the liner. Drilling continued to 3061.1 m where the bottom hole assembly twisted off. The hole was sidetracked again and drilling continued to base of the Early Cretaceous where 7" liner was set. Further drilling to final TD went without significant difficulties. The well was drilled water based with spud mud down to 745 m, polymer mud from 745 m to 8313 m, sea water/Drispac/Soltex mud from 8313 m to 9304 m, polymer mud from 9304 m to 1