35/12-1

General

The well 35/12-1 was drilled on the eastern border of the block 35/12 against a north-south oriented main fault, which is the eastern limit of the Uer Terrace. The primary purpose of the well was to test the hydrocarbon potential in sandstones of the Late Jurassic Sognefjord Formation. A secondary objective was to test the reservoirs of the Brent and Dunlin Groups.

Operations and results

Well 35/12-1 was spudded with the semi submersible rig Treasure saga on the 27 February 1992 and was drilled to TD at 3020 m in Early Jurassic (Early Pliensbachian - ?Sinemurian) rocks. The well was drilled with spud mud down to486m,with gel mud from 486 m to 1020 m,and with KCL mud from 1020 m to TD.

The well penetrated mainly claystones with minor sandstone intervals in the Nordland and Rogaland Groups. Shetland and Cromer Knoll Groups consisted mainly of claystones with limestones and marls. The well encountered 37 m of Draupne. Top Heather Formation was penetrated at 2398 m. The reservoir quality in the Heather Formation was poor. The formation consists of siltstone and some thin beds of fine sandstones with low porosity.

The sandstones in the Sognefjord Formation and the Fensfjord Formation sandstone had better reservoir quality with porosities around 20% in the Fensfjord Formation. Sandstones were also present in the Brent and Dunlin Groups. Some weak traces of hydrocarbons were observed in sandstone lamina on cores from the Upper parts of the Heather Formation. Weak traces of shows were recorded also in the Fensfjord Formation and into the Brent Group. Petrophysical evaluation showed that the sandstones of Jurassic age were water filled. The well was terminated 17 m into what was initially believed to be basement rocks, but which was shown by post-well analyses to be undifferentiated Early Jurassic sediments about 120 meters shallower than prognosis. Three cores were cut in the Heather Formation from 2415 m to 2458.5 m.