Realistic permeability distributions in faults and sediments: The key to predicting fluid flow in sedimentary basins

The permeability of faults and their sedimentary host rocks is a critical input for models of fluid flow in sedimentary basins. Permeability of sedimentary rocks can vary by orders of magnitude over short distances due to variations in sedimentary facies, as well as being strongly anisotropic. Structural features also affect permeability, with faults acting as fluid conduits or barriers depending on the nature of the sedimentary host rock. Constraining these variations in permeability is challenging where outcrops are lacking and drillhole data are sparse. This study describes a workflow using stratigraphic forward modelling to estimate the permeability distribution (both magnitude and anisotropy) in sedimentary rocks and associated faults, which is then used in fluid flow simulations. Permeability is represented as a tensor in the global coordinate system, enabling the use of an unstructured mesh that is independent of stratigraphic layering. The workflow is demonstrated in a sub-basin of the Proterozoic McArthur Basin of northern Australia. A range of fault permeability scenarios are explored, where fault permeability is a function of host rock properties. The simulation results demonstrate the importance of capturing the direction of permeability anisotropy in dipping strata, as well as highlighting the effect of different fault permeability scenarios. The workflow is particularly well-suited to scenarios where there are sufficient boreholes to constrain a stratigraphic forward model, but insufficient to determine the permeability distribution by interpolation. Potential applications include mineral and hydrocarbon exploration, groundwater studies, contaminant dispersal modelling, and CO2 sequestration.