25/5-1

General

Well 25/5-1 was drilled on a Jurassic structure straddling the two blocks 25/5 and 25/2. It is located near the crest of a westward tilted Jurassic fault block in the northern part of block 25/5. The northern extension of this structure was drilled in 1977 by well 25/2-6 which is located In the southern part of the neighbouring block 25/2, in a down dip position relative to well 25/5-1. Well 25/2-6 was plugged and abandoned with limited oil shows in sandstones of the Early Jurassic Statfjord Formation. The main objectives of well 25/5-1 were to test the hydrocarbon potential of the middle Jurassic Vestland Group sandstones and the Early Jurassic Statfjord Formation sandstones up dip of well 25/2-6.

Operations and results

Wildcat well 25/5-1 was spudded 12 May 1987 by Norcem semi-submersible rig Nortrym and completed 1 August 1987 at a depth of 3430 m in the Triassic Group. Drilling proceeded without significant problems. There was no sign of shallow gas. One core was cut in the Draupne Formation between 2916 and 2925 m. Top reservoir (Hugin Formation) was encountered at 2984 m. Five cores were cut between 2990 - 3081 m in the Hugin and Sleipner formations and into the Drake Formation. The logs showed that the whole reservoir section contained oil down to base Sleipner / top Drake Formation, which formed a lithological sand / shale contact at 3060 m. RFT pressure measurements indicated an oil/water contact at ca 65 m below this level, implying a vertical oil column of 166 m. Due to this the hole was decided to be sidetracked to find the oil/water contact in the Sleipner Formation. Top Statfjord came in at 3232 m, and 3 cores were cut in the interval 3235 - 3291 m. There were shows down to 3264 m; below this depth the sandstones were wate