30/6-9

General

Well 30/6-9 was drilled on the Gamma structure on the Oseberg Field in the northern North Sea. The Gamma structure lies on the west side of the Alpha structure and is separated from it by a large northwest-southeast fault. The primary objectives of well 30/6-9 were to test hydrocarbon accumulations in the Brent Group and find additional hydrocarbon accumulations within the Early Jurassic. This was the first well located on the Gamma structure. Planned depth for the well was ca 3360 m or 75 m into the Triassic Lunde Formation.

Operations and results

Wildcat well 30/6-9 was spudded with the semi-submersible installation Nortrym on 28 August 1982 and drilled to TD at 3476 m in the Late Triassic Lunde Formation. No significant problems occurred while drilling the well. The well was drilled with seawater, bentonite and hi-vis pills down to 975 m, with KCl/polymer mud from 975 m to 2750 m, and with lignite/lignosulphonate/freshwater mud from 2750 m to TD

Weak to strong shows were reported mainly in soft limestone stringers in the lowermost part of the Lista Formation in the Late Paleocene, in the Danian, and through the Maastrichtian. Further shows above the Brent Group were reported in cuttings in limestones from 2410 to 2422.5 m, just above the Late Jurassic unconformity.

The main target, Brent Group was penetrated from 2458 to 2620 m. It was hydrocarbon bearing over the entire interval with the gas/oil contact calculated from FMT pressure recordings at ca 2520 m. This is the same, as the GOC on the Alpha structure. No oil/water contact was encountered. The net pay in the Brent Group is calculated to be 98 m giving a net/gross ratio of 0.60. The average porosity is 22.7% with