6507/12-1

General

Wildcat well 6507/12-1 was the first well to be drilled offshore Mid-Norway. It was drilled to test the stratigraphic sequence between seabed and at least 500 m below "reflector E" as defined in the licence agreement. The primary target was a mapped Intra Jurassic seismic reflector at a depth of approximately 2575 m. This reflector was interpreted to be associated with a Middle to Early Jurassic sandstone sequence. The secondary target was represented by possible sandstone sequences between the mapped Base Cretaceous reflector and the Intra Jurassic reflector. Thirdly there was a small vertical closure in the basal part of the Tertiary sequence that could have prospective interest.

The well is Type Well for the Båt Group, the Tare Formation and the Naust Formation. It is Reference Well for the Fangst Group.

Operations and results

The well was spudded with the semi-submersible installation Byford Dolphin on 1 July 1980 in a water depth of 225 m, and drilled to a total depth of 3713 m in Late Triassic Red Beds. The well was drilled with spud mud down to 778 m, with Gypsum PAC mud from 778 m to 1448 m, and with Lignosulfonate/PAC mud from 1448 m to TD.

The well penetrated a section of 1105 m below reflector E and thus meets the requirement set in the work programme for licence 059.

The well encountered a Cenozoic sequence of 1679 m and the Tertiary succession was, at the time the well was drilled, subdivided into lithostratigraphic units according to Deegan & Scull's nomenclature for the northern North Sea. The well proved a slightly thicker Tertiary sequence than expected. The seismic leg interpreted to represent Base Tertiary proved to be related to a tuff sequence (Tare Formation).

The Top Cretaceous reflector was easily determined from acoustic and density logs. The base of the Cretaceous was encountered in the well at 2032 m. The prognosed depth was 1975 m. The Cretaceous seque