35/12-4 S

General

Well 35/12-4 S was drilled on the Ryggsteinen Ridge/Uer Terrace structural elements in the Northern North Sea. The objective was to appraise 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). The gas discovered in the Sognefjord Formation is deemed unproducible due to low permeabilities. Only the Fensfjord Formation and the Brent Group are appraisal targets. The majority of the volumes are expected to be located in the Brent Group. The Statfjord Formation was a tertiary objective.

Operations and results

Appraisal well 35/12-4 S was spudded with the semi-submersible installation Songa Delta on 23 April 2011 and drilled to TD at 3585 m (2766 m TVD) in the Early Jurassic Statfjord Formation. No significant problem was encountered in the operations. The well was drilled with sea water and hi-vis sweeps down to 501 m, with Aquadril mud from 501 m to 1315 m, and with Carbosea oil based mud from 1315 m to TD.

Base Cretaceous unconformity/top Heather Formation was penetrated at 2503.5 m (2080 m TVD). A sharp increase in the NearBit Resistivity LWD tool and increased gas values were seen on penetrating the Fensfjord Formation at 2526.5 m (2095 m TVD). The sandstones had an average porosity of 24 % when using a 10 % porosity cut-off. A gross oil column of approximately 14 m TVD was found in the Fensfjord Formation with an OWC at 2552 m (2112 m TVD) based on the pressure gradients. On penetrating the top of the Ness Formation at 3070.5 m (2441 m TVD), an increase in background gas was noticed. The Ness sandstones had an average porosity of 21.7 %, when using a 10% porosity cut-off. A gross oil column of approxim