6506/12-1

General

Well 6506/12-1 was drilled on the Alpha structure in the northwest part of the block. The main objective was middle Jurassic sandstones in an anti form structure. The secondary and tertiary objectives were Early Jurassic and Triassic sandstones on the same structure. Late and Early Cretaceous were also considered possible zones of hydrocarbon accumulations. Further objectives, of a more general exploratory nature, included the sampling of potential source rocks. Total depth was to be in rocks of Triassic age, or 4000 m in order to satisfy the licence commitment.

The well is Type Well for the Tofte, Lange, and Lyr Formation. It is Reference Well for the Cromer Knoll Group and for the Springar, Nise, and Kvitnos Formations.

Operations and results

Wildcat well 6506/12-1 was spudded with the semi-submersible installation Ross Isle on 16 August 1985 and drilled to TD at 4924 m in the Early Jurassic sediments of the Åre Formation. Drilling down to, and cementing the 20" casing, went without problems. While testing the casing a leak was discovered. No influx or loss of fluid was observed. Setting a cement plug in the interval 540-590 m solved the problem. A leak-off test equal to 1.34 g/cm3 below the 20" casing shoe was considered to low, and a cement squeeze was performed, after which a formation integrity test gave 1.64 g/cm3 without leak off. A cement squeeze also had to be performed to obtain a satisfactory leak-off test below the 13 3/8" casing shoe. Pore pressures were considerably below prognosed down to this depth. While preparing to run the 9 5/8" casing a sealing ring was dislodged and had to be milled. Down to 4317 m maximum deviation was 3.7 ° and difference between measured and true vertical depth was not more than 1 m. The last part of the well was however more problematic in this respect. At 4925 m it was decided to stop the drilling as the angle had built up too much, and an RFT-tool was stuck i