26/4-1

General

Well 26/4-1 was the first well drilled in the Stord Basin. The well was designed to test a Paleocene mound, and sandstones of Jurassic age within a footwall closure. The Paleocene sandstone was prognosed to come in at 2268 m. Another primary objective was to gain information on reservoir quality and hydrocarbon source. A secondary target was the Sleipner Formation prognosed at 2783 m. Prognosed TD was 3500 m MSL.

Operations and results

Wildcat well 26/4-1 was spudded with Wi1h. Wilhelmsen semi-submersible installation Treasure Scout on 8 may 1987 and completed 17 July 1987 at a depth of 3690 m in Triassic Hegre Group. Drilling proceeded without significant problems, except for several occurrences of lost circulation due to increasing formation pressure in Tertiary rocks. The well was drilled with seawater and bentonite down to 236 m, with seawater / bentonite /PAC from 236 m to 723 m, with KCl / Polymer mud from 723 m to 2680 m, and with seawater / polymer from 2680 to TD.

The Paleocene Mound (Ty Formation sand) came in at 2246 m. Pressure measurements taken 7 m into the mounds displayed normal pressure conditions, and the sandstone proved to be water bearing. The Jurassic Draupne Formation came in at 2637 m with a total thickness of 88 m. An extremely radioactive layer was found between 2688 and 2693 m. The Sleipner Formation sandstone came in at 2820 m. Top Statfjord Formation came in at 3308 m. Sands in Jurassic (Hugin and Statfjord Formations) displayed a very slow white cut fluorescence and traces of oil on cores, but were otherwise found dry. Post well geochemical analyses revealed very good source rock intervals in the Draupne Formation (oil prone) and the Statfjord Formation (oil and gas prone). Draupne shale and Sleipner coal are immature with Vitrinite reflectance around 0.5 %Ro, while the Statfjord coals may be marginally mature with Vitrinite reflectance around 0.6 %Ro and Tmax approaching 450 °C.

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