STATISTICAL ANALYSIS OF AN OUTCROPPING POINT BAR DEPOSIT INFORMS CONSTRUCTION OF GEOLOGICALLY REALISTIC 3D GEOCELLULAR MODELS

Sigmoidal surfaces and the strata they bound are widespread in the sedimentary record, formed in a variety of depositional environments over a wide range of spatial scales. Lateral accretion of a fluvial meander bend is recorded as sigmoidal surfaces and, as well as the intervening strata, provides key evidence for the evolutionary history of a point bar. Strata bounded by sigmoidal surfaces comprise a range of facies that commonly change drastically in both down-dip and along strike directions. In this study, we document detailed facies and stratigraphic relationships in an outcropping Late Cretaceous point bar deposit of the Horseshoe Canyon Formation in southeastern Alberta, Canada. We perform a series of statistical analysis and devise a comprehensive approach for incorporation of outcrop-derived data directly into stochastic facies modeling workflows.

Detailed sedimentological observations were collected in 35 measured sections in order to characterize six facies throughout the point bar deposit. Stratigraphic architecture was mapped in the field using a high-resolution dGPS unit. The model has a grid cell size of 5 m x 5 m x 0.3 m (x, y, z) to represent the fine-scale heterogeneity without compromising computational ability. The stratigraphic architecture and measured section data provide the basis for a series of statistical analyses, including net-to-gross, vertical and horizontal transition probabilities, and vertical and horizontal facies proportion curves. Results of the statistical analyses are incorporated into 3D probability models which are used to guide the distribution of facies throughout the model using a truncated Gaussian simulation. Results capture the complex facies relationships along and across sigmoidal surfaces and from older to younger deposits, toward abandonment.The approach used in this study is broadly applicable to any setting where sigmoidal clinoform architectures are characterized by varied facies distributions within and between stratigraphic surfaces. By generating quantitative results through statistical analyses, the data derived from this study can be applied to more poorly-constrained point-bar deposit reservoirs such as those in the vast Athabasca oil sands of northeastern, Alberta, Canada.