6507/8-4

General

Well 6507/8-4 was designed to drill the Heidrun North Structure, a horst block northeast of the Heidrun Field situated in the transition zone between the Nordland Ridge to the north and the Halten Terrace to the southwest. The primary objective of the well was to test sandstones of Early Jurassic age. The well would also test the geophysical and structural interpretation and improve the paleontological, geological and geochemical understanding of the area.

Shallow gas warning was given at 608 m, 745 m and 686 m, the last one classified as a medium/ high risk anomaly. Problems with gumbo clay and sloughing shale had been experienced in the Eocene / Paleocene sections in the Haltenbanken area.

Operations and results

Wildcat well 6507/8-4 was spudded with the semi-submersible installation Deepsea Bergen on 14 June 1990 and drilled to TD at 2560 m in the Triassic Grey Beds. Apart from some tight hole spots, drilling proceeded without significant problems. The well was drilled with seawater and hi-vis sweeps down to 654 m, with seawater and CMC EHV mud from 654 m to 1555 m, with gypsum/polymer mud from 1555 m to 2100 m, and with gel/ligno mud from 2100 m to TD. Shallow gas was encountered at 596 m and at 686 m.

The only shows reported above the target reservoir were on claystones at 2102 m and at 2104 m. Top reservoir (Åre Formation) was encountered directly underlying Late Cretaceous sediments at 2124 m. The hiatus was from the Early Jurassic, Sinemurian to the Late Cretaceous, Santonian. The well proved gas and oil in the Åre formation. The GOC was set at 2142 m and the OWC at 2251.5 m. Shows continued down to 2290 m.

A total of 170.25 m core was recovered in eleven cores, all from the Åre Formation in the interval 2128 to 2318 m. Twenty-five sidewall cores were attempted and 22 were recovered. An FMT fluid sample was taken at 2158.5 m. It contained only 500 cc mud filtrate due to plugging. Another sample wa