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Application of Forward Stratigraphic Modelling in Deep-Water Shale Basins; Insights from the Devonian Horn River Basin, BC, Canada

Abstract

The Middle-Upper Devonian Horn River group (HRG) is a major shale gas resource in British Columbia, Canada, currently undergoing for exploration and development. We have developed a detailed sequence stratigraphic framework through the application of sedimentological and geochemical analysis to an extensive set of long cores and a detailed subsurface well log correlation. We recognise multiple systems tracts, including highstand, transgressive, lowstand, and fallingstage systems tracts, and multiple major surfaces such as sequence boundary and basal surface of forced regression. This permits us to understand the fundamental architecture of the reservoir and to characterize the depositional settings. We then applied a forward stratigraphic modelling to generate a simulated 3D stratigraphic model for the HRG that we compare to the observed stratigraphic patterns, enabling us to test importance of parameters such as basin bathymetry, timing and magnitude of sea level cycles, and the volume of extra- and intra-basinal input. Forward stratigraphic modelling is a powerful tool to predict reservoir potential in sedimentary basins, although it has rarely been applied to shale basins. We applied Dionisos software from IFP (Institut Francais du Petrole). The complex nature of the basin bathymetry, derived from several core-based data set, allowed us to visualize a realistic history of the basin evolution. Results suggest that the Horn River Basin was evolved in nine 3rd order (0.5 Ma) cycles. Even though shale basins can be formed in various water depths, we successfully generated our model using a maximum depth of 300 m. Models invoking a shallower initial water depth of 150 m did not successfully recreate the stratigraphy of the entire section. For the 300 m-depth model, we used a single clastic sediment source located in the south, consistent with sedimentological and ichnological findings. The main parameters that controlled our model are (1) sediment supply, (2) sediment discharge rate and (3) eustatic sea level variation. The sediment supply and discharge rate were generally enough to generate different sequences; however, varying sea level variations were almost equally important. The results presented in this study show forward stratigraphic modelling can be applied to unravelling sequence stratigraphic units in other shale basins.