34/7-23 S

General

Well 34/7-23 S is located on the Vigdis Field on Tampen Spur in the Northern North Sea. Located 5200 meters north-northwest of the H-Sentral 34/7-21 oil discovery, the well was primarily designed to test for reservoir presence and hydrocarbons in the Top Draupne Sequence of Portlandian and Ryazanian age. In the case of a discovery, pressure communication with well 34/7-21 would be tested. Secondary objectives of the well included lowermost Early Cretaceous sandstones found oil bearing in 34/7-21, and intra Oxfordian sandstones which were found to yield oil in well 34/7-21 A. Both these sandstones are thin and below seismic resolution. An additional objective was to test the presence of sandstone in Paleocene.

Operations and results

Well 34/7-23 S was spudded with the semi-submersible installation Vildkat Explorer on 22 February 1994 and drilled to TD at 3375 m (2889 m TVD) in the Middle Jurassic Tarbert Formation. The subsea Jurassic target location coincided with the pipeline which connects the Snorre TLP to the Statfjord C platform. To avoid any mechanical problems with the rigs anchors, the spud location was chosen to be located 1400 meters east of the Base Cretaceous target location and the borehole was designed as a westward deviated well. Special H2S equipment was mobilized when H2S was observed during coring in the upper part of the reservoir. For operational reasons it was decided to interrupt coring and take a FMT sample. An additional 10 meters were drilled from 3096 down to 3106 m to get a rathole for the FMT logging tool. This interval was thus not cored. The well was drilled with spud mud down to 1175 m, and with KCl mud with a polyalkyleneglycol additive (BP DCP 208) m from 1175 m to TD.

In the Nordland, Hordaland and Rogaland Groups, the well penetrated mainly clay/claystone with some beds of sand, except for the sandy Utsira Formation between 955 - 1144 m (934 - 1114 m TVD). In the Shetland Group clay stones wi