2/7-26 S

General

Well 2/7 26 S is located on the Embla Field in the Central Graben of the North Sea. It was designed to test the pre-Jurassic sandstones, which had shown commercial quantities of hydrocarbons in the 2/7-20, 2/7-21 S, and 2/7-23 S wells. The objective of the well was to confirm the presence of hydrocarbon bearing sandstones in the western fault block of the structure and to establish the productivity of this reservoir section through a program of well testing and coring. Well location and TD was chosen so that both the upper and lower sandstone members of the pre-Jurassic sequence would be penetrated. The target location was 300 m to the south of the 2/7-9 well at Base Cretaceous level. The reservoir section was expected to be highly fractured and over-pressured. Shallow gas was expected since gas had been encountered in all wells drilled from the template location over the 2/7-20 well.

Operations and results

Appraisal well 2/7 26 S was spudded with the semi-submersible installation West Delta on 20 March 1991 and drilled to TD at 4848 in Devonian rocks. The well was drilled deviated from a template located over the 2/7-20 well to penetrate the target reservoir section in the western fault block of the Embla structure. Minor shallow gas was detected in sandy zones with an increase in background gas from 4 to 64 units. Apart from some failures when logging and some stuck pipe experiences, drilling proceeded without significant problems. The well was drilled with seawater and hi-vis sweeps down to 575 m, with KCl/PAC mud from 575 m to 4125.5 m, and with Enviromul oil based mud from 4125.5 m to TD.

The 9 5/8" casing was set in claystones of the Lower Cretaceous, Rødby Formation. The remaining Lower Cretaceous section including Sola, Tuxen and Åsgård Formations was penetrated, followed by a Late Jurassic sequence consisting of 3 m Mandal Formation and 82 m Farsund Formation. The top of the reservoir sands were encountere