Numerical study of NMR relaxation responses in synthetic clayey sandstone by dual-scale modeling

Nuclear Magnetic Resonance (NMR) relaxometry is a common technique for petrophysical characterization of sedimentary rocks. The standard interpretation NMR relaxation response assumes that the fast diffusion limit valid whole pore space, allowing to translate transverse components into apertures. However, porous media naturally exhibit multiple length scales. between different sized pores may modify rate, weakening relationship with corresponding size populations. Focusing on sandstones, we investigate impact coupling depending kaolinite amount, spatial distribution and temperature. A series synthetic clayey sandstone models clay amounts morphological distributions (pore-lining, pore-filling laminated) are generated based micro-CT image an actual Bentheimer sandstone. dual-scale random walk simulation resolved multi-porosity utilized avoid problems in near interface exchange regions typical effective medium representations. Simulations provide spatially dynamics magnetization porosity results indicate increased temperature amount lower micro-porosity allows higher micro- macro- regions. Pore-lining demonstrates stronger diffusional effects, leading overestimation micro-porosity. We further discuss NMR-estimated permeability via SDR Coates models.