A Digital Rock Physics Approach to Modeling Permeability Changes with Solid Phase Formation in Reservoir Porous Media

Abstract This paper illustrates the application of pore-scale numerical simulation to evaluate permeability changes due to solids precipitation with Digital Rock Physics (DRP). A DRP modeling workflow is used to quantify permeability changes due to solid phase formation (precipitation of gas hydrates) based on their deposition morphology on the pore scale. Virtual representations of a sandstone sample from the Bentheimer outcrop are created using micro-computer-tomography (micro-CT) scanning images and state-of-the-art segmentation algorithms. The binarized images (pores and grains) are systematically altered with morphological operations, i.e., erosion and dilation, to represent precipitation of solids in a pore filling and a grain/pore coating morphology, respectively. The Lattice Boltzmann Method (LBM) for single-phase fluid flow simulations is used to calculate the absolute permeability of the original and the altered 3D rock models directly on the pore structure. The changes of permeability are plotted against the solid saturation to compare to empirically derived and idealistic, mathematical descriptions. We verify the suitability of the high-resolution micro-CT images for fluid flow simulations using guidelines from the technical literature. Due to the high permeability and porosity of the sample, a threshold algorithm for image binarization based on the Otsu criterion is used and yields a sample porosity of 0.28 and permeability of 4.77 Darcy in z-direction. These values for porosity and permeability are validated from measurements using a CMS-300 apparatus on the actual rock sample. Erosion is applied to the segmented pore space to represent the pore filling deposition morphology and dilation is applied to the segmented grains to represent the grain/pore coating deposition morphology of methane hydrates. A third-degree polynomial trend relating the permeability reduction with the hydrate saturation is established for the first time using the actual pore structure rather than idealized and empirically derived laws, which are non-unique, depending on which theoretical method is chosen. The presented methodology could be used to evaluate the effect of solids precipitation on scenarios like the productivity of petroleum reservoirs, and injectivity in carbon sequestration or gas storage projects.