2/7-21 S

General

Well 2/7-21 S was drilled to appraise the "South Eldfisk structure", now known as the Embla Field, located in the Central Graben of the North Sea. It was the third well drilled on the structure, a pre-Cretaceous fault block forming the boundary between the Grensen Nose to the west and the Feda Graben to the east. The primary objective was to test the sandstones that tested oil in the 2/7-9 and 2/7-20 wells. It was anticipated that the proposed location would encounter reservoir quality sands similar in nature, thickness, and depth as in the 2/7-20 well. Closure of the structure is provided by normal down faulting to the North, South and West. Closure to the east is by the Lindesnes Ridge reverse fault. Vertical sealing is provided by the Early Cretaceous Shales. No shallow gas was expected in this area, and no major obstacles other than high formation pressure in the reservoir. If successful, the well was planned to constitute a second drainage point for future field development.

Operations and results

Appraisal well 2/7-21 S was drilled deviated from a three-slot template located at the 2/7-20 well to a location 1020 m to the southeast. The well was spudded on the 21st June 1989 and drilled using the semi-submersible installation Ross Isle to a Total Depth of 5039 m (4706 m TVD RKB) in rhyolitic igneous rocks of probable Early Devonian age. The well was drilled without significant problems, except for MWD failures. Shallow gas was encountered at 586.7 m but caused no problems. The well was drilled without problem using SOLTEX Actaflow water based mud down to 4232 m at the base of the Cretaceous section, where 9 5/8" casing was set. The remaining 8 1/2" and 5 7/8" hole sections in the well were drilled using Invermul oil based mud.

Oil-bearing reservoir quality sands were encountered at 4313 m. No definitive oil-water contact could be seen. The section consisted of undefined lithostratigraphy of pr