Surface nuclear magnetic relaxation and dynamics of water and oil in macroporous media.

Proton nuclear spin-relaxation studies on water- or oil-saturated granular packings and limestone rocks allow estimating surface molecular dynamical parameters. Measurements were performed at various conditions of temperature, magnetic field strengths, and pore size. We show by low field NMR relaxation that changing the amount of surface paramagnetic impurities leads to striking different pore-size dependences of the relaxation times T1 and T2 of liquids in pores. These dependences are well supported by surface-limited or diffusion-limited relaxation models. Surface relaxivity parameters rho(1) and rho(2) are deduced from the pore-size dependence in the surface-limited regime. We evidence the frequency and temperature dependence of the surface relaxivity rho(1) by field cycling NMR relaxation and relevant theoretical models. The typical frequency dependence found allows an experimental separation of the surface and bulk microdynamics in porous media. Several surface dynamical parameters, such as diffusion coefficients, activation energies, time of residence, and coefficient of surface affinity, were therefore determined. The methods presented here give a powerful analysis of the surface microdynamics of confined liquids, which can be applied to the study of oil-bearing rocks.