15/12-21

General

The 15/12-21 Grevling well is located on the south-western margin of the Hidra High, approximately 18 km north of the Varg field in the southernmost part of the Viking Graben. The primary objective was to test the Middle Jurassic Hugin and Sleipner formations in a crestal position on the structure. The Triassic Skagerrak Formation was a secondary objective.

Operations and results

A 12 1/4" pilot hole was drilled to 1195 m to check for shallow gas. No shallow gas was encountered. Well 15/12-21 was spudded with the jack-up installation Mærsk Guardian on 15 March 2009 and drilled to TD at 3310 m in the Late Triassic Skagerrak Formation. The well was drilled with Seawater and sweeps down to 221 m, with a water based KCl mud from 221 m to 1193 m, and with Carbosea oil based mud from 1193 m to TD.

The top of the Hugin reservoir was encountered at 3031 m, 15m deeper than prognosis. The Sleipner Formation reservoir came in 21m shallow, at 3059 m, and top the Triassic 11 m shallow, at 3122 m. The Hugin, Sleipner and upper Skagerrak formations all proved to be oil bearing with a total pay of 67 m. No oil water contacts were encountered within the well. However, two vertical pressure barriers were interpreted; a top Sleipner coal at 3059 m (3017 m TVDSS), which separates the Hugin and Sleipner oil-bearing sandstones, and an intra-Triassic shale at 3164 m (3122 m TVDSS), which separates oil bearing Skagerrak sandstones above from water bearing Skagerrak sandstones below. No oil shows were recorded above reservoir level in the well. In the Triassic oil shows were seen down to 3179 m, 15 m below the oil-down to contact in the Skagerrak Formation.

Two cores of a total of 88.26 m were