Onshore and Irish Sea
Published:January 01, 2019
All of the components of an exhumed Devonian petroleum system occur in Orkney. These include a good quality mature source rock to bitumen-bearing sandstone reservoirs, with several separate accumulations that could have held about 1.88 billion barrels of oil. The exhumed system presents an excellent analogue for deeply buried petroleum systems offshore. Whilst lighter oils are now absent, reported oil shows occur, commonly associated with faults cutting the Eday Group. On Orkney, Middle Devonian source rocks (750 m thick) were thick lacustrine laminites (fish beds) representing some 30% of the sequence. RockEval and vitrinite analyses show the organic matter is good quality Type I and II and within the early oil window. These source rocks underwent burial until Permian inversion. Several exhumed reservoirs occur on Orkney in aeolian and fluvial sandstones with porosities from 15 to 25%. These reservoirs have been ‘breached’, losing the light-end hydrocarbons, leaving pore space oil stain and bitumen residues. Thin fluvial and sheet-floods sands found within the lake cycles have bitumen residues and provided connectivity between the thicker reservoir units. All types of trap are found including a major, broad anticline running north–south on Mainland Orkney and an unconformity with fault traps and pinchouts.
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Paleozoic Plays of NW Europe
CONTAINS OPEN ACCESS
Despite successful production from Carboniferous and Permian reservoirs in the southern North Sea and onshore Netherlands and Germany, Paleozoic hydrocarbon plays across parts of NW Europe remain relatively under-explored both onshore and offshore. This volume brings together new and previously unpublished knowledge about the Paleozoic plays of NW Europe to describe significant additional exploration opportunities outside and below existing plays.
The volume contains papers on Paleozoic plays in the North Sea, Irish Sea, onshore UK, France and Switzerland. They highlight how improvements in seismic data quality and the availability of previously unpublished well datasets form the basis for improved understanding of local to regional interpretations that move forward from generalized basin development models. The improved structural trap and source rock basin definition feeds to better constrained, locally variable burial, uplift, maturation and migration models. Particularly notable are the significant mapped extents and thickness of Paleozoic source, reservoir and seal rocks in areas previously dismissed as regional highs and platforms.