6507/7-4

Wellbore history

General

Appraisal well 6507/7-4 was drilled in the northern part of the Haltenbanken area, some 190 km west of the Norwegian coast. It was drilled to evaluate the "B" prospect in the intensely faulted zone that lies at the intersection of the Nordland Ridge in the northeast and the Halten Terrace in the south. The prospect was in a southward plunging horst block formed by a Late Jurassic tensional fault system. Well 6507/7-4 was drilled in a down dip position relative to discovery well 6507/7-2 and the prime objective was to establish the oil/water contact in sandstones of the Middle Jurassic Tomma Formation.

Operations and results

Well 6507/7-4 was spudded with the semi-submersible installation Nortrym on 6 November 1985 and drilled to TD at 2850 m in the Early Jurassic Tilje Formation. Due to adverse weather conditions in the first week of operations spudding of the well was made difficult, and 4.5 days were lost as WOW in this phase. Swelling clays (gumbo) caused some problems in the 17 1/2" section. The upper part of the core barrel in core no 3 ruptured, unfortunately exactly in the section around OWC. Otherwise operations proceeded without significant problems. The well was drilled with sea water and gel sweeps down to 1021 m and with gypsum/polymer mud from 1021 m to TD.

The Tomma Formation sandstones (Garn Formation) was prognosed at 2455 m, and encountered at 2449 m. The Garn Formation was found oil bearing. Oil shows were observed on core no 1 from 2444.5 m (driller's depth) down to 2490.7 m. It was described as a uniform strong yellow show with even white cut down to 2463 m when the show became m