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Petroleum Systems of the Northern Williston Basin: A Quantitative Basin Modelling Assessment


1D, 2D and 3D modelling of petroleum systems of the northern Williston Basin was conducted to identify, analyse and characterize fundamental geological processes involved in the generation, migration and entrapment of hydrocarbon within Phanerozoic strata. The 3D Basin Model consists 8 2D transects with 38 control wells, each with a unique 1D model. The assessment takes into account. Paleo-erosion magnitudes for the Tertiary, Sub-cretaceous, Sub-Jurassic, Sub-Triassic, Sub-Devonian and Mid-Ordovician erosional events were derived using the McKenzies lithospheric stretching methodology augmented by traditional methods. Paleobathymetry data was also calculated using the McKenzie methodology and calibrated using reported biostratigraphic data. Measured bottom hole geothermal data, calculated present day heat flow, simulated paleo-heat flow solutions and full geochemical analyses (i.e. RockEval, organofacies, kinetics) were applied to the maturation solutions of each source rock unit. There are a number of significant results. Firstly, modelled crustal stretch factors (ßcrust) agree with the CONCRUST refraction seismic data, that indicates 3km to 4km of crustal thinning. Secondly, McKenzie's derived paleobathymetry data concur with biostratigraphic data, permitting the creation of palobathymetry maps for the Early Turonian Upper Colorado Second White Specks formation and the Upper Devonian/Lower Mississipian Lower and Upper Bakken Shale members (150m, 250m and 250m max paleobathymetry respectively). Thirdly, exhumation maps reveal trends in erosional magnitude such as the Mid-Ordovician and the Sub-Devonian NW-SE trend, whereas a NE-SW trend characterizes the Sub-Jurassic, the Sub-Cretaceous and the Tertiary erosion maps. Lastly, source rock and hydrocarbon generation models show that the Lower Paleozoic source rock units within the southern Saskatchewan (i.e. Upper Cambrian to Ordovician) reach maturity by the late Paleozoic. In contrast, other Paleozoic sources (e.g. Bakken) enter the main generation stage in the Late Cretaceous to the Paleogene time using standard kinetic parameters. Using formation specific kinetics (e.g. Ea, A, w-factor, Sorg) with organofacies, identifies ‘micro kitchens’ of early generation. Not only does this 3D basin model of the northern portion of the Williston Basin identify and replicate existing oil/gas pools, but identifies ‘micro kitchens’ of probable generation for stratigraphic units of the mid to late Paleozoic.