Quantification of Reservoir Geometries and Facies Proportions in Wave-Dominated, Shallow Marine Sandstones: ABSTRACT

Abstract

To reliably appraise shallow marine hydrocarbon reservoirs, it is important to have a quantitative understanding of the geometries of parasequences, and the spatial distribution of facies within them. This study discusses the quantification of parasequence geometries and intraparasequence facies proportions in wave-dominated, shallow marine strata exposed in large scale outcrops in the Book Cliffs, Utah. The Grassy Member of the Blackhawk Formation consists of two, wave-dominated shallow marine sequences. Sequence 1 of the Grassy Member comprises two parasequences. Analysis of the depositional architecture of Parasequence 1 and Parasequence 2 shows they have very different geometries. Parasequence 1 is an aggradational-progradational parasequence which thickens gradually basinward. In contrast, Parasequence 2 is strongly progradational and shows and abrupt thickening in a basinward direction. Although Parasequence 1 and 2 have different dipsection geometries, analysis of changes in shoreface facies proportions in both, shows they have similar trends in the overall distribution of facies from proximal to distal positions. The Book Cliffs outcrops enable a complimentary analysis of strike geometries and facies proportions to also be undertaken. This study shows that within two progradational parasequences which have different geometries, there is a degree of predictability in the overall distribution of the wave-dominated shallow marinemore » shoreface facies. This suggests that, with an understanding of the large-scale depositional architecture of wave-dominated sandstones in the subsurface, the overall changes in the proportion of shoreface facies within that system can be predicted.« less