18/10-1

General

Well 18/10-1 is located in the Egersund Basin in the North Sea, ca 16 km southeast of the 17/12-1R Bream Discovery. It was designed to test a seismic structure on the same trend as the Bream discovery. The primary target was to test possible hydrocarbon accumulation in Jurassic sandstones on. Planned TD is about 150 to 200 m below Jurassic sandstone in a shaly-sandy sequence of Early Jurassic or top of Triassic.

Operations and results

Well 18/10-1 was spudded with the semi-submersible installation Dyvi Alpha on 19 October 1979 and drilled to TD at 2800 m in the Triassic Skagerrak Formation.

A thick Late Jurassic shale sequence with limestone stringers was penetrated before reaching the target Middle Jurassic sands. The sands (Sandnes and Bryne Formations) were encountered at 2405 m, close to prognosis. The reservoir consisted of two zones separated by a thin shale barrier between 2427 and 2433 m. Based on FMT and DST pressure measurements the upper zone appeared slightly overpressured relative to the lower, suggesting a compartmentalized reservoir. The reservoirs were found hydrocarbon bearing and an OWC was found at 2437 m in the lower zone. The lithology below the target reservoir section, from 2483 m to TD, was predominantly sandstone, fine in the upper part, becoming medium to coarse downwards. Frequent thin interbeds of shale and marl, occasionally also thin stringers of limestone were encountered. The sequence was entirely water bearing. Weak direct fluorescence and cut appears at 2420 m, becoming very good in the intervals 2423 m to 2430 m and 2433 m to 2440 m, then the shows get weaker and disappear below 2444 m.

Organic geochemical analyses showed an immature well all through (%Ro = 0.5 at TD). TOC in the Late Jurassic shale increased gradually from ca 0.8% at top Jurassic to ca 1 % at 2200 m. A peak TOC is reached in the Tau Formation with 4.5 % TOC in cuttings and 6.9 % in a sidewall core. The hydroge