6406/3-5

General

Well 6406/3-5 was designed to explore the Lambda structure and was the first well on the structure. The Lambda structure is a flat-lying horst situated in the NE corner of the block.

The primary purpose of the well was to find hydrocarbon accumulations of significant amounts in the Middle and Lower Jurassic sandstones of the Fangst Group and Tilje Formation. Secondary objectives were to verify the interpretation regarding the structural closure towards north, and to verify the geophysical and structural interpretation and improve the geological, paleontological and geochemical understanding of the area. The well was planned to TD in the Åre Formation.

Operations and results

Wildcat well 6406/3-5 was spudded with Smedvig Drilling semi-submersible rig West Delta on 3 April 1988 and drilled to a total depth of 4283 m in the Early Jurassic Tilje Formation. Shallow gas was registered at 570 m. After pulling out to cement this zone, it was impossible to get back into the hole again. After a new spud 3 May, the 30" was set at 418 m, and 20" at 538 m. A new shallow gas zone was registered at 813 m, and the mud was weighted to 1.35 g/cm. The circulation was lost at 1116 m, and the section was cemented. After this drilling progressed with a mud weight of 1.25 g/cm3. This resulted in lost circulation at 1340 m. Both times it was assumed that that the circulation was lost in the zone around 562 m. The hole was cemented back and drilled to 607 m where a new leak-off test up to 1.34 g/cm was performed. This time there were no problems with the drilling to 1749 m (setting depth of 9 5/8" casing) with mud weight of 1.25 g/CM3. Further drilling to TD proceeded without significant problems. The well was drilled with spud mud down to 545 m, with gypsum/polymer mud from 545 m to 3841 m, and with gel/lignite/lignosulphonate mud from 3841 m to TD.

Top Fangst was encountered at 3817 m. There were weak shows in the top ten