17/4-1

General

Well 17/4-1 was drilled on a NNE-SSW trending monocline in the Ling Depression between the Sele High and the Utsira High /Patch Bank ridge. The objective was to investigate the sedimentary section down to the pre-Permian, and particularly to test the hydrocarbon potential of the Mesozoic sands and Zechstein dolomites. Furthermore, Early Permian and/or pre-Permian reservoirs were to be evaluated if present.

Operations and results

Wildcat well 17/4-1 was spudded with the semi-submersible installation Ocean Viking on 15 June 1968 and drilled to TD at 3997 m in conglomerate in the Early Permian Rotliegend Group. Initial drilling to 444 m was with seawater, and the returns were to the sea floor. The 17 1/2" hole was drilled out using an LFC-LC/sea water type mud, and the 13 3/8" casing shoe was set at 1803 m. From this depth the mud system was salt saturated. The 12 1/4" hole was drilled down to 3942 m from where the hole diameter was reduced to 8 1/2". An inverted oil-base mud was used from 2900 m to TD.

Sandstones were encountered in the Jurassic and Triassic. They had medium to good porosities, but generally poor permeabilities due to calcite cement. The pre-Zechstein conglomerate was very tight with no porosity. On top of this there were nearly 1200 m of evaporites, apparently undisturbed by halokinesis. The evaporites were overlain by around 300 m of continental Triassic deposits. The Jurassic consisted of fluvial sandstones overlain by carbonaceous dark shales belonging to the Late Jurassic "hot" shale (Draupne Formation). This shale was penetrated at 2122 m and is 95 m thick in the well position. No samples of any kind was recovered from this interval, but analysis of caved cuttings believed to originate from Draupne indicated TOC in the range 2 % to 7 % with potential for oil and gas. The Draupne formation is immature in the well. The Early Cretaceous marine, low energy shales range in age