2/4-16

General

Well 2/4-16 was drilled on the eastern margin of the Feda Graben North of the Albuskjell and Ekofisk Fields in the North Sea. Geologically the area consists of three sub-platforms. These are separated by large NW-SE striking normal faults down-faulted to the southwest and stepping down to the Feda Graben in the southern part of the block. The 2/4-16 well is located in the centre of the licence area on the same down faulted segment as the blowout wells 2/4-13, -14 and -15. Shallow gas was predicted from seismic anomalies at 10 different levels, and several precautions and actions were carried out to be able to handle potential gas-charged shallow gas.

The main objective for the well was to test the Late Jurassic, expected to contain a thick sand resting unconformable on the Middle Jurassic. This objective was the basis also for the 2/4-14 well. A secondary objective for the well was to penetrate the Middle Jurassic and 150 m into the Triassic sequence to test for possible hydrocarbon bearing sandstones sequences.

Operations and results

Wildcat well was spudded with the semi-submersible installation Treasure Saga on 7 May 1991 and drilled to TD at 4996 m in the Middle Jurassic Bryne Formation. Shallow gas was detected at 522, 606, 628 and 675 m during drilling of 9 7/8" pilot hole. While drilling through very hard chalk rocks in the 12,6" section severe problems with the drilling equipment was experienced. The hard rocks also caused 8.5 days of delay due to ten washouts and fishing jobs. In addition the vibration together with high temperature caused twelve failures to the MWD tools, and also problems related to equipment deliveries. When drilling down to 4996 m the top drive saver sub had to be changed out due to a washout. During change of saver sub, the well started flowing uncontrolled up through the drill string, and the drill pipe was cut with the shear ram. Fifty-eight days were spent from shearing the pi