Nuclear magnetic resonance (NMR) relaxation experimentation is an effective technique for non-destructively probing the dynamics of proton-bearing fluids in porous media. The frequencydependent relaxation rate T −1 1 can yield a wealth of information on the fluid dynamics within the pore provided data can be fit to a suitable spin diffusion model. A spin diffusion model yields the dipolar correlation function G(t) describing the relative translational motion of pairs of 1 H spins which then can

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... be Fourier transformed to yield T −1 1 . G(t) for spins confined to a quasi-two-dimensional (Q2D) pore of thickness h is determined using theoretical and Monte Carlo techniques. G(t) shows a transition from three-to two-dimensional (2D) motion with the transition time proportional to h 2 . T −1 1 is found to be independent of frequency over the range 0.01-100 MHz provided h 5 nm and increases with decreasing frequency and decreasing h for pores of thickness h < 3 nm. T −1 1 increases linearly with the bulk water diffusion correlation time τ b allowing a simple and direct estimate of the bulk water diffusion coefficient from the high-frequency limit of T −1 1 dispersion measurements in systems where the influence of paramagnetic impurities is negligible. Monte Carlo simulations of hydrated Q2D pores are executed for a range of surfaceto-bulk desorption rates for a thin pore. G(t) is found to decorrelate when spins move from the surface to the bulk, display three-dimensional properties at intermediate times and finally show a bulk-mediated surface diffusion (Lévy) mechanism at longer times. The results may be used to interpret NMR relaxation rates in hydrated porous systems in which the paramagnetic impurity density is negligible.