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The Southern Norwegian Shelf (56°-58°30^primeN) has proved to be one of the most prolific hydrocarbon provinces in Europe. Recoverable reserves of about 2 billion bbl of oil are found predominantly in Upper Cretaceous-Danian age chalk and Jurassic sandstones. The excellent quality of seismic data, moderate-dense well control, and the detailed geochemical evaluations of the Kimmeridge Clay, the principal source rock, make the Southern Norwegian Shelf an ideal area for hydrocarbon generation studies.
A geochemical analysis of the area contained 4 basic steps: (1) construction of a 9-layered 3-dimensional grid summarizing the burial history of the sediments, using well control and seismic data, (2) calculation of geothermal gradients, (3) source rock analysis to investigate variations in thickness and richness throughout the study area of the Kimmeridge Clay, and (4) maturation study based on the results of the 3 initial steps.
Major factors affecting hydrocarbon accumulations in the structural and stratigraphic closures of the study area include the amount of oil generated within the catchment areas of the various closures, and particularly in the case of the chalk fields, the level of hydrocarbon generation of the Kimmeridge Clay directly under the crest of the structure and the presence of faults to act as conduits for vertical migration of hydrocarbons from the Upper Jurassic Kimmeridge Clay to the Upper Cretaceous-Danian chalk. The expulsion and migration efficiency (hydrocarbons in place/hydrocarbons generated within the catchment area of individual closures) for tested closures averages approximately 8% for the study area, with individual culminations having values as high as 40% or as low as 0% based in part on the previously mentioned factors.
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