34/7-12

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Well 34/7-12 is a replacement well for well 34/7-11, which was junked for technical reasons. It is located in the Tampen Spur area in the Northern North Sea. Its overall purpose was to assess the hydrocarbon potential in the "B"-structure in the southern part of the block. The primary objectives were to establish the thickness and reservoir quality of the prospective Brent the Brent Group in Group, and to determine the OWC. The secondary objectives were to assess the potential of the Dunlin Cook Formation reservoir, the Statfjord Formation and the upper part of the Triassic Lunde unit B/C reservoir section. TD was prognosed to 2900 m.

Operations and results

Wildcat well 34/7-12 was spudded 20 m north of the 34/7-11 location. It was drilled with the semi-submersible installation Treasure Saga on 11 October 1987 and drilled to TD at 2784 m in the Late Triassic Lunde Formation. The well was drilled without significant technical problems. The well was drilled with spud mud down to 852 m and with KCl mud from 852 m to TD.

The Brent Group came in at 2169 m, and Statfjord Formation at 2606 m. Lunde Formation was encountered at 2763 m. Oil/water contact was defined in the Ness Formation at 2250 m.

The Brent Group, from 2169 to 2340.5 m (171.5 m thick) comprised the sandy Tarbert Formation,the interbedded shaly and sandy Ness Formation, the sandy Etive and Rannoch Formations and at the base the conglomeratic Broom Formation. The Dunlin Group was penetrated from 2340.5 to 2606 m (265.5 m thick), comprising the shaly Drake Formation at the top, the Cook Formation with interbedded sandstone and claystone, the Burton Formation with claystone and minor sandstone and the Amundsen and Calcareous Amundsen Formations having clay stones with minor limestone. The Statfjord Formation, 157 m thick from 2606 to 2763 m, was dominated by sandstones with minor to interbedded claystone. The Late Triassic upper Lunde Formation was encountered at 2763