2/11-4

General

Well 2/11-4 was drilled on the Lindesnes Ridge in the Southern North Sea. The objective was to delineate the Valhall discovery made by well 2/8-6 in 1975. The target was the Late Cretaceous chalks in the Tor and Hod formations.

Operations and results

Appraisal well 2/11-4 was spudded with the jack-up installation Dyvi Beta on 20 March 1978 and drilled to TD at 2858 m in the Late Cretaceous Rødby Formation. No significant problems were encountered in the operations. The well was drilled with sea water and hi-vis pills down to 390 m, with sea water/gypsum mud from 390 m to 2559 m, and with Magcobar oil based "Oilfaze" mud from 2559 m to TD.

The well penetrated a normal Quaternary and Tertiary sequence. Good oil shows with free oil present in the mud was observed in siltstone and claystone from 1400 to 1800 m in the upper part of the Hordaland Group. Occasional spotty oil shows in claystones and limestones (direct and cut fluorescence) were recorded from 1800 to 2250 m. The Cretaceous Chalk was penetrated at a depth of 2587 meters some 23 meters higher than prognosed. The objective Tor Formation reservoir proved to be hydrocarbon bearing with a gross pay section of 18 meters and oil saturations up to 62%. Hydrocarbon saturation in the Hod Formation was insignificant due to low elevation on the structure. Fair to excellent oil shows were seen in the reservoir section down to 2607 m. Below 2607 m scattered poor shows were seen down to 2619 m.

Coring commenced at 2582.5 meters, 4.5 meters above top Chalk, to ensure recovery from the uppermost part of the pay section. A total of 5 conventional cores were attempted over the interval 2582.5 m to 2619 m. Cores no 1 and 2 ha