34/11-4

General

Block 34/11 is geographically located in the eastern part of the Tampen Spur, adjacent to the western controlling fault of the North Viking Graben. Structurally 34/11 is situated over a large, complex fault terrace down thrown to the south east of the Tampen Spur. The Mats Segment, which was tested with this well, is situated in the southwest part of block 34/11, and represents an easterly extension of the Gullfaks Gamma discovery in block 34/10. The Brent Group reservoir within the Gullfaks Gamma structure is within a high pressure, high temperature geological environment being at over 4000 m depth, with temperatures of 150 deg C. The main objective of the appraisal well 34/11-4 was to appraise additional hydrocarbon reserves in the Brent Group. Secondary objectives were to improve the geological / geophysical engineering parameter database, provide a key velocity calibration point to aid depth conversion, and to give a better understanding of the hydrocarbon characteristics, fluid contacts and distribution within the southern part of the 34/11 block.

Operations and results

Appraisal well 34/11-4 was spudded on 9 December 1998 with the semi-submersible installation "Transocean Arctic" and drilled to 3938 m. An unsuccessful cement job on the 9 7/8" casing resulted in backing off several joints of the casing. The casing was cut and retrieved from below the 13 3/8" shoe. The well was then sidetracked (34/11-4 T2) from 3580 m on 7 February 1999 and the 9 7/8" casing was successfully run and cemented at 3939 m. The T2 track was drilled to TD at 4438 m in the Early Jurassic Cook Formation, then logged and sampled (water and hydrocarbon samples). The initial well track was drilled with water based "Quadrill" mud containing 2 & 5 % polyols, a glycol-additive. The T2 track was drilled oil-based. Finally, an 8 1/2" sidetrack, 34/11-4 T3, was kicked-off at 4098 m on 31 March 1999 and drilled to 4210 m. T