Effects of Image Resolution on Sandstone Porosity and Permeability as Obtained from X-Ray Microscopy

Estimating porosity and permeability for porous rock is a vital component of reservoir engineering, and imaging techniques have to date focused on methodologies to match image-derived flow parameters with experimentally identified values. Less emphasis has been placed on the trade-off between imaging complexity, computational time, and error in identifying porosity and permeability. Here, the effect of image resolution on the permeability derived from micro-X-ray microscopy (micro-XRM) is discussed. A minicore plug of Bentheimer sandstone is imaged at a resolution of 1024x1024x1024 voxels, with a voxel size of 1.53m, and progressively rebinned to as low as 32 voxels per side (voxel size 48.96m). Pore-scale flow is modeled using the finite volume method in the open-source program OpenFOAM((R)). A sharp drop in permeability between images with a voxel size of 24 and 12m suggests that an optimal speed/resolution trade-off may be found. The primary source of error is due to reassignment of voxels along the pore-solid interface and the subsequent change in pore connectivity. We observe the error in permeability and porosity due to both image resolution and thresholding values in order to find a method that balances an acceptable error range with reasonable computation time.