33/12-4

General

Well 33/12-3 was drilled on the Statfjord structure in the Tampen Spur area. It was designed to test the erosional escarpment on the east flank of the structure for possible trapping of hydrocarbons in an area downfaulted to the Statfjord Field pay section to the west. Primary objectives of the well were the Early Jurassic Statfjord Group sands and possible Middle Jurassic Brent Formation sands. Well 33/12-3 was junked due to technical problems. The rig was moved 30 m and re-spudded as replacement well 33/12-4.

Operations and results

Appraisal well 33/12-4 was spudded with the semi-submersible installation Nordskald on 17 May and drilled to 2896 m in Late Triassic sediments in the Statfjord Group. The well was drilled with seawater down to 495 m and with water based lignosulphonate mud from 495 m to TD.

The Middle Jurassic Brent Group was encountered at 2675 m, ca 55 m high to prognosis but, as anticipated, well below the Brent oil/water contact of 2609 m (2584 m MSL) in the upthrown block of the field. Scattered poor to fair hydrocarbon indications were noted in the cores but gas readings were low. Average core porosity in the sands is 23 %, ranging from two to 29 %. Measured horizontal permeabilities average 604 mD and range between 0.01 and 2028 mD. The CPI log indicated some 40 feet of prospective net pay with 23 percent average porosity and 53 percent average water saturation.

The top of the Statfjord Group was penetrated at 2757 m, only 2 m low to prognosis. Core 4 at the top of Statfjord recovered sand, siltstones and claystones with no shows. However, poor shows were recorded above and below the cored section. Using a 65% water saturation cut-off Schlumberger's pre