NMR Relaxation Modelling in Porous Media with Dual-Scale-Resolved Internal Magnetic Fields

Abstract A pore-scale forward modelling approach for NMR relaxation responses of sandstones incorporating their dual-scale nature is presented. The utilises X-ray micro-CT images to capture inter-granular porosity and scanning electron microscopy reconstruct clay regions via a resolved micro-structure model. key calculating the response with development internal magnetic field calculation. This achieved by separation near- far-field effects in dipole approximation periodic micro-structures, latter which take local pocket into account. Tri-linear interpolation image before calculation further reduces errors transition between coarse- fine-scale structure, final discretisation level matching model across whole domain. method validated against direct calculations media at full resolution applied Bentheimer sandstone. Measured simulated $$T_2$$ T 2 responses, including time distribution shape, are excellent agreement distributions gradients highest spatial as well diffusion-averaged effective reported.