Tectonic Controls on Oil and Gas Occurrences in the North Sea Area
Published:January 01, 1989
C. Cornford, J. Brooks, 1989. "Tectonic Controls on Oil and Gas Occurrences in the North Sea Area", Extensional Tectonics and Stratigraphy of the North Atlantic Margins, A. J. Tankard, H. R. Balkwill
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From deposition of source rocks, via maturation and migration, to alteration of oil in the reservoir, tectonics exert a fundamental control in the North Sea area. The southerly development of an elongate arm of the Boreal Sea during the Late Jurassic resulted from an early rifting attempt of the northern North Atlantic. This deep-water trough favored the development of bottom-water anoxia, while rapid sédimentation also enhanced the chances of preservation of algal debris falling from an upper oxygenated photic zone.
Maturation of the Upper Jurassic-basal Cretaceous source rock was then controlled by subsidence and heat flow in what is generally described as a techtonically quiescent period of thermal subsidence. If source rock deposition occurred as a result of crustal thinning and graben formation, the consequent thermal subsidence predicts falling sédimentation rates andheat flow. The facts, however, dispute this model, with increasing rather than decreasing (decompacted) sédimentation rates. With this continued subsidence oil generation has occurred from the Cretaceous to the Holocene.
Whereas long-distance oil migration is controlled essentially by tectonic tilt, local sedimentological changes at fault scarps interbedding source rock and coarser elastics can enhance the expulsion of hydrocarbons from the source rock unit.
Bacterial alteration in the reservoir is related to heat flow as a result of a 60-80 °C cutoff for active bacterial growth, and more speculatively by the presence of late-stage transtensional (open) faults allowing oil to reach near-surface reservoirs and ground water with bacteria to be introduced into the traps.
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Extensional Tectonics and Stratigraphy of the North Atlantic Margins
Stimulated by the wealth of frontier exploration data and deep seismic surveys about the North Atlantic margins, this publication was crafted to provide a comprehensive analysis of North Atlantic extension. The 40 papers in this volume are divided into 6 sections: concepts, North Atlantic perspectives, North American margins, European-African margins, North Sea and Barents Shelf, and analogs. This book is concerned primarily with the circum-North Atlantic data base. It is largely biased toward presentation and interpretation of data rather than being model driven. The book includes comparative stratigraphic columns for basins of the North Atlantic margins.