35/12-4 A

General

Well 35/12-4 A is a sidetrack to well 35/12-4 S on the Ryggsteinen Ridge/Uer Terrace structural elements in the Northern North Sea. Both well bores are appraisal wells to the 35/12-2 Grosbeak discovery, a multi-level discovery, with hydrocarbons in the Sognefjord Formation (gas), in the Fensfjord Formation (oil) and in the Ness Formation (oil). Well 35/12-4 S proved a 14 m oil column in the Fensfjord Formation and a 40 m oil column in the Ness Formation. Well bore 35/12-4 A was sidetracked to appraise the oil in the Ness Formation in a position northwards and down flanks of 35/12-2 and 35/12 -4 S.

Operations and results

Appraisal well 35/12-4 A was kicked off on 26 June 2011 from the primary well bore 35/12-4 S. The well was sidetracked at 902 m MD through a windows in the 13 3/8" casing. It was drilled with the semi-submersible installation Songa Delta to TD at 3413 m (2585 m TVD) in the Middle Jurassic Rannoch Formation. No significant problems were encountered in the operations. The well was drilled with Carbo-sea oil based mud from kick-off to TD.

While the Draupne Formation was not present in the primary well the sidetrack well penetrated a thick Draupne Formation section from 2836 m to 2967 m (2239.5 m to 2318 m). No Fensfjord Formation was encountered in the 35/12-4 A sidetrack. The Middle Jurassic Ness Formation came in at 3230 m (2475 m TVD), but was shaled out above the previous known contact from 35/12-2 and 35/12-4 S at ca 2485 m TVD. Weak hydrocarbon shows were however seen in the upper part of the Ness Fm. The underlying water wet sandstones had an average porosity of 19 % when using a 10 % cut-off.

No cores were cut in the sidetrack well. A total of 20 p