Minimising the impact of sub-resolution features on fluid flow simulation in porous media

Abstract

Resolution of micro-computed tomography (micro-CT) images of rocks affects flow simulation results, especially on low resolution images where the pore-grain boundary is not well resolved. However, there are two occasions where conducting flow simulations on low resolution images may be beneficial. The first case is when computation costs need to be reduced, and second is when high-resolution scanned images are unavailable and segmentation on available low-resolution images is difficult due to uncertainty at the pore boundary. A novel analytical formulation, the concentric pipes method, is introduced in this paper to include the effect of sub-resolution features in flow simulation. For the first case, we compare porosity, permeability, pore connectivity, and the velocity field obtained from applying different approaches to solve for flow on images with sub-resolution features. We find that the permeabilities obtained from downsampled images using the concentric pipes method have 13.2% errors on average compared to results from high-resolution images, while computation time decreases by at least 80%. For the second case, three phase segmentation can be applied to low resolution images and the concentric pipes method can be applied to the uncertain region which allows flow in the system to be solved. Permeability estimations in this case are within 0.5% error for a sandstone image and 11% error for carbonate images. We also simulate transport of particles on downsampled images and compare the transport properties with the high-resolution images.