25/11-5

General

Well 25/11-5 was drilled ca 4 km north west of the 25/11-1 Balder discovery well on the Utsira High in the North Sea. The well was designed to evaluate a sand build up and/or structural closure at the Middle Paleocene horizon top. The location was mapped structurally high to the adjacent wells 25/11-1, 25/11-2, 25/10-1, and 25/10-3.

Operations and results

Appraisal well 25/11-5 was spudded with the drillship Drillmaster on 3 April 1974 and drilled to TD at 2164 m in Triassic red-grey clays, and grey-green shale. Sloughing shale was the only drilling problem and this was overcome by converting the Drispac mud system to a ligno-gel seawater mud system. The well was drilled with Drispac from approximately 1000 to 1400 m, and with lignosulphonate/gel/seawater from ca 1400 m to TD.

The well penetrated the Utsira Formation and a Skade Formation sand and then entered a ca 700 m thick section of shales belonging to the lower Hordaland Group before top Balder formation was encountered at 1661 m. Significant oil bearing sands in the interval from 1714 to 1771 m were confirmed by sidewall cores and Schlumberger electric logs. The lower part of this interval tested oil at good rates. Additional shows in traces of sand in cuttings at 1838 - 1847 m were believed to be sloughings from the oil sand above.

One conventional core was cut from 1723.3 to 1725.5 m. Six attempts at FIT's were attempted with one successful at 1744.1 m. This test recovered 0.33 Sm3 gas, 4.5 l oil, 2.3 l filtrate and 0.8 l mud.

The well was permanently abandoned on 8 May1974 as an oil appraisal.

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