33/6-1

General

Well 33/6-1 is located in the Marulk Basin northwest of the Snorre Field in the southeastern sector of block 33/6. The location was selected on the crestal area of the most attractive feature in the licence: a fault bounded, tilted block. The closure was considered dependent upon the sealing properties of the NE-SW fault to the south of the prospect. The primary objective of the well was to test the Middle-Early Jurassic Brent-Statfjord reservoirs. Planned TD was in the Late Triassic Hegre Group

Operations and results

Exploration well 33/6-1 was spudded on April 9, 1979 in 306 m water depth, the deepest drilling location to that date. Semi-submersible installation Fernstar was used to drill the well. Due to soft bottom conditions and problems with stabilizing the temporary guide base on the sea floor the well was re-spudded twice, the last and successful attempt on April 15. The well reached TD at 3900 m in the Early Jurassic Statfjord Formation. The well was drilled with seawater and pre-hydrated bentonite down 434 m, with seawater/HPD polymer/bentonite from 434 m to 695 m, with KCl/Dextrid/seawater from 695 m to 1690 m, and with lignosulphonate/fresh water from 1690 m to TD.

The most significant horizons, the top of the Paleocene Seismic Marker and top Cretaceous, came in 13 meters lower and 37,5 meters higher than expected, respectively. The pre-Cretaceous section deviated significantly from prognosis. This was caused by a very crude depth conversion model due to lack of well control in the area and a much thinner Brent thickness than prognosed. All pre-Cretaceous targets were found however. The Late Kimmerian unconformity was encountered 133.5 m high to prognosis. The Late Jurassic shale was 65.5 m thick, 35 meters thicker than prognosed and consisted of 30 m of Draupne Formation plus 35.5 m of Heather Formation.

The primary target Brent Group was penetrated at 3603 m, 97 meters higher than prognosed, and on