2/7-20

General

Well 2/7-20 was drilled on the "South Eldfisk structure", later called Embla. The 2/7-9 well, drilled in 1973, tested oil at uneconomic rates from a thick pre-Late ?Jurassic sand sequence on this structure. Well 2/7-9 established a 111 m pay section with average porosity of 13% and 55% oil saturation. A clear OWC was found at 4387 m MSL. Following a 1986 re-evaluation of the test it was concluded that the poor test results might have been due to mechanical problems. Subsequently the 2/7-20 well was spudded to test the previously encountered sandstones. The objectives of the well were to test "economic" flow rates from sands on the South Eldfisk structure below the Late Jurassic shales of the Mandal Formation. At the time of drilling the cost of a subsea completion had been estimated to be US$ 12 million which meant that flow rates in excess of 286 m3 oil/day were considered economic. Well 2/7-20 was placed on a separate and higher fault block in the structure than the one drilled by 2/7-9.

Operations and results

Wildcat well 2/7-20 was spudded with the semi-submersible installation Dyvi Stena on 15 October 1987. The well was re-spudded three times because of collapsed hole problems. After drilling riserless to 608 m the lower part of the hole collapsed after encountering a gas sand that resulted in the loss of drill pipe. The well was sidetracked at 234 m, and 13 3/8" casing was set above the Eocene at 2439 m. A drilling break was encountered at 4084 m. After drilling a further 2 m, 100% sands with good shows were circulated up. High pressures together with the long section of open hole necessitated plugging back and sidetracking immediately below the 13 3/8" casing shoe. No logs were run at TD in this hole before plugging back. Drilling the sid