34/10-42 S

General

Block 34/10 covers a structurally complex area located in the Tampen Spur area of the Viking Graben. The Tampen Spur is characterized by a series of rotated fault blocks, where the major faults generally have throws towards the east and stratigraphic dips westwards. The Gullfaks Gamma structure sits on a fault terrace, down thrown from the Gullfaks Sør Field. This terrace also covers the Kvitebjørn area. The structure is a complex, faulted culmination, with a dip closure in all directions. The Gullfaks Gamma area straddles the 34/10 - 34/11 block boundary. The majority of the defined prospective elements, lie within block 34/10

The primary objectives for drilling well 34/10-42 S were to appraise economical Brent hydrocarbon reserves updip from well 34/10-23 and to test the Brent erosion model and thereby to enable a Gullfaks Gamma Field PDO. The hydrocarbon type was to be tested. A secondary objective was to test possible additional reserves in the Cook and Statfjord Formation if the well was extended through these formations. Finally, the well should add data to the field parameter database and provide a key velocity calibration point for time-depth conversion.

Operations and results

The appraisal well 34/10-42 S was spudded with the semi-submersible installation "Transocean Arctic" on 15 July 1999 and drilled to TD at 4520 m (4378 m TVD RKB) approximately 40 m into the Early Jurassic Cook Formation. It was drilled deviated to avoid shallow gas Class II warnings. The well was drilled with sea water and hi-vis pills down to 1133 m, with KCl / polymer / glycol mud from 1133 m to 3666 m, and with oil based mud from 3666 m to TD. The reservoir tops came in deeper than the geological prognosis indicated. The top of the Tarbert and Cook Formations were found 174 m and 112m deeper, respectively. Both the Brent group and the Cook Formation proved to be water wet, indicating a sealing fault between well 34/10-23 and 34/10