| Summary: | Dissertation (Ph.D.) University of Alaska Fairbanks, 2013 I interpret sedimentary facies and depositional environments from the Albian-Cenomanian Nanushuk Formation of Alaska's North Slope from sedimentary structures observed in core samples and in outcrop in the National Petroleum Reserve - Alaska (NPRA) and surrounding areas, and support these interpretations with supplemental analyses of geophysical well logs and ������Ar/�_��_Ar dating of volcanogenic deposits. The results have implications for the reservoir characterization of a shallow, frozen oil field at Umiat, Alaska, and for interpretations of the Colville foreland basin. In the central Brooks Range foothills the Nanushuk Formation comprises shallow marine and non-marine fades associations that can be grouped into marine-distributive and river-distributive systems. In wells at Umiat, Alaska, shoreface and wave-influenced deltaic sandstones (marine-distributive systems) occur at the base of the Nanushuk Formation, followed by a marine transgression and subsequent progradation of a delta complex (river-distributive system). The shift from marine-distributive to river-distributive systems is related to shelf building processes during the Albian-Cenomanian. Marine-distributive systems occurred at or near the shelf edge in a high-energy coastal environment, whereas river-distributive systems rapidly prograded over the shallow Nanushuk shelf following transgression. Marine-distributive conditions resumed when rapidly progradational river-distributive systems reached the shelf edge. This pattern occurs in the Umiat, Wolf Creek, and Grandstand No. 1 subsurface wells. The reservoir quality of the Nanushuk Formation varies strongly with facies. Well-sorted sandstones at the top of upward-coarsening successions in both marine- and river-distributive units have the highest permeabilities within the Nanushuk Formation. Marine-distributive units have low permeability anisotropy in contrast to river-distributive units due to better sorting in wave-influenced ...
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