34/7-22

General

Well 34/7-22 is located between the Gullfaks and Snorre fields on Tampen Spur in the Northern North Sea. The main objective was to prove hydrocarbons and reservoir quality of a Brent Group prospect named the STWB prospect, defined by structural closure towards east and north, dip closure towards south, combined with fault seal against the Main Tordis Fault (MTF) towards west. Sands within Paleocene, Cretaceous, and Late Jurassic were secondary objectives.

Operations and results

Wildcat well 34/7-22 was spudded with the semi-submersible installation West Delta on 15 August 1993 and drilled to TD at 2507 m in the Early Jurassic Drake Formation. Since possible shallow gas levels had been predicted, a 9 7/8" pilot hole was drilled. The Nordland Group consisted mainly of claystone except for the sandy Utsira Formation, which came in at 907 m. On the seismic, top Hordaland was interpreted to coincide with a structural high which was considered to be a clay diapir. The "clay diapir" consisted, however, almost entirely of sandstone which partly belongs to the Utsira Formation and the upper part of the Hordaland Group. The unexpected large amounts of sand caused operational problems due to instability and the drill string got stuck at 1086 m, on 17 August. The string was backed off and the well was re-spudded on 18 August. The casing program was re-designed to penetrate and stabilize the sandy Utsira Formation and Hordaland Group with a weighted mud system. After re-spud, drilling commenced as planned. The well was drilled with spud mud down to 1329 m, and with KCl mud with glycol from 1329 m to TD.

No sand or hydrocarbons were found within the Paleocene and Cretaceous (Campanian) intervals, but at 2178.5 m, a water wet Intra-Draupne Formation sand was penetrated. At 2184 m the Heather Formation was encountered with a thickness of 40 m, 31m thicker than prognosed. Top reservoir, corresponding to Top Tarbert Formation, B