Explicit calculation of nuclear magnetic resonance relaxation rates in small pores to elucidate molecular scale fluid dynamics

Nuclear magnetic resonance (NMR) spin-lattice (T−1 1 ) and spin-spin (T−1 2 ) relaxation rate mea- surements can act as e ective non-destructive probes of the nano-scale dynamics of 1H spins in porous media. In particular, fast- eld-cycling T−1 1 dispersion measurements contain information on the dynamics of di using spins over time scales spanning many orders of magnitude. Previously- published experimental T−1 1 dispersions from a plaster paste, synthetic saponite, mortar and oil- bearing shale are re-analysed using a model and associated theory which describe the relaxation rate contributions due to the interaction between spins ensembles in quasi-two-dimensional (Q2D) pores. Application of the model yields physically-meaningful di usion correlation times for all systems. In particular, the surface di usion correlation time and the surface desorption time take similar values for each system suggesting that surface mobility and desorption are linked processes. The bulk uid di usion correlation time is found to be 2-5 times the value for the pure liquid at room temperature for each system. Re-analysis of the oil-bearing shale yields di usion time constants for both the oil and water constituents. The shale is found to be oil-wetting and the water T−1 1 dispersion is found to be associated with aqueous Mn2+ paramagnetic impurites in the bulk water. These results escalate the NMR T−1 1 dispersion measurement technique as the primary probe of molecular-scale dynamics in porous media yielding di usion parameters and a wealth of information on pore morphology