Abstract: A method for calibrating a direct flow simulation of a rock sample involves providing a 3D image of a rock sample and generating a segmented structural image of the rock sample from the 3D image by selecting voxels to represent either a pore space or a solid material. Fluid flow is simulated on the segmented structural image with a direct flow simulation. A 3D spatially-resolved fluid velocity map is generated for one or more fluid phases at a pore-scale resolution using pulsed field gradient nuclear magnetic resonance imaging. The simulated fluid flow and the 3D spatially-resolved fluid velocity map are compared to calibrate the direct flow simulation across the rock sample.