35/10-4 S

General

Well 35/10-4 S was drilled to test the Stålull prospect on the Marflo Spur in the North Sea. The primary objective was to prove petroleum in Middle and Early Jurassic reservoir rocks (the Brent group and the Cook formation). The secondary objectives were to prove hydrocarbons in Late Jurassic reservoir rocks (Intra Viking Group sands), and to test the reservoir potential in the Paleocene (Intra Balder sands/Sele formation).

Operations and results

Wildcat well 35/10-4 S was spudded with the semi-submersible installation Deepsea Bergen on 14 August 2018 and drilled to TD at 4010 m (3810 m TVD) m in the Early Jurassic Cook Formation. Operations proceeded without significant problems. The well was drilled with seawater and hi-vis pills down to 772 m, with KCl/GEM/polymer mud from 772 m to 1406 m, with XP-07 oil based mud from 1406 m to 3456 m, and with HT XP-07 and BaraECD oil-based mud from m and with MUD from 3456 m to TD.

In the Paleocene, the well encountered a 17-metre thick water-bearing sand package with good reservoir properties. The Heather Formation came in at 3353 m and consisted of claystone with numerous interlayered sandstones. A total of 10 metres of the top 50 meters was sandstones with poor reservoir quality, and in this interval, there was an oil show (direct and cut fluorescence) at 3370 m, while live oil was sampled at 3358.3 m. A second sand-rich Intra-Heather interval was penetrated from 3513 to 3556 m, but without any hydrocarbon indications. The Brent group was encountered at 3625 m (3425 m TVD), about 210 metres thick, of which 40 metres are effective reservoir sandstone, mainly with poor to moderate reservoir properties. Top Cook Formation was encountered at 3845 m (3645 m TVD). About 75 metres of the gross