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Architectural Modeling of an Outcropping Tidally Influenced Point Bar Deposit: Sedimentologic and Stratigraphic Impacts on Connectivity


Three-dimensional modeling of point bar deposits, specifically inclined heterolithic strata (IHS), has been a recent focus of numerous studies due to the challenges faced during development of the Athabasca Oil Sands in Alberta, Canada. Dense well data, 3-D seismic volumes, and outcrops of the bitumen-bearing McMurray Formation, indicate that IHS is locally prevalent. Production and reservoir modeling results indicate that IHS impacts development of the resource. In order to constrain reservoir-scale architecture of IHS and deduce their impact on connectivity, outcropping point bar deposits of the Horseshoe Canyon Formation (Campanian-Maastrichtian) at Willow Creek, Alberta are being investigated. The objectives of this study are to: (1) create a 3-D geocellular model that includes facies distribution and internal stratigraphic architecture information of an outcrop-constrained, tidally influenced point bar deposit; and (2) investigate the impact of variably continuous inclined siltstone beds on connectivity. A 3 km-long transect through a single point bar deposit is exposed along a series of tributaries to the Red Deer River valley in the central Alberta study area. Detailed sedimentologic characteristics were compiled from 32 measured sections and are used to populate lithologic parameters within the 3-D model. Individual intra-point bar lateral accretion and erosional surfaces were surveyed using a high resolution (10 cm) differential GPS unit. Outcrop data was then imported into Petrel and individual surfaces projected in 3-D; surface data were used to extend the architecture and facies distribution into areas of limited outcrop coverage. Widely applied point bar depositional models describe relatively simple processes of lateral accretion on the inner bend of channel meanders and erosion on the outer cut-bank, with little consideration of intra-point bar erosion and re-orientation. However, the point bar deposit of this study is characterized by intra-point bar erosion surfaces which bound distinct lateral accretion packages that are each characterized by unique orientations of point bar migration. These surfaces play a key role in the continuity of siltstone layers which may act as baffles or barriers to fluid flow. The reservoir model suggests discontinuous siltstone beds that result from intra point bar erosion increase connectivity substantially, with a positive effect on reservoir performance.