6407/6-2

General

Well 6407/6-2 was drilled on a structure in the western part of the block. The structure has two distinct highs, and the target for this well was on the northern high. The primary objective for the well was to test possible hydrocarbon accumulation in sandstones of middle Jurassic age (Fangst Group). Secondary objectives were seen in sands near base Cretaceous (Cromer Knoll Group), in Early Jurassic sandstones (Tilje Formation), in sandstones within the Åre Formation, and in the Triassic Grey- and Red Beds. The top hole and Tertiary sections of this well were expected to contain shallow gas, possibly at a depth of 570 m. Possibly, also swelling, overpressured Early Eocene Red/Brown claystone could be encountered. The prognosed depth was 4150 m, or rocks of Triassic age.

Operations and results

Wildcat well 6407/6-2 was spudded with the semi-submersible installation West Vanguard on 4 October 1985. It was abandoned at a depth of 523 m due to a blow out. The blow out probably was caused by gas from a shallow sand pocket at 505 m. Gas samples from the blow out were analysed and found to be gas generated by bacteria at shallow depths.

The 20" casing had not yet been set so the blow-out preventer (BOP) had not been installed when the incident happened. At 20:50 hours in the evening an increase in the penetration rate from 40 to 700 m/hour was observed. Drilling was immediately stopped and the bit pulled out of hole. The hole was circulated for 35 minutes. A 3-m3 mud loss was observed. After gas had been circulated out drilling of a 12 1/4" pilot commenced from 508 m to 516 m. Here background gas again increased. After again circulating out the gas drilling continued to 524 m where the drill string was pulled out 15 m for a new stand connection. The well now started flowing uncontrolled and pumping of kill mud started. This did not stop the blow out. Gas flowed onto the deck of the rig and at 23:20 hours the gas exploded.