Surface nuclear magnetic relaxation and dynamics of water and oil in granular packings and rocks

Low field proton nuclear spin-relaxation at variable magnetic field strength and temperature provides surface dynamical parameters such as surface diffusion coefficients, activation energies, time of residence and coefficient of surface affinity. These parameters were extracted from measurements on grain packs and natural oil-bearing rocks. On grain packs, we show first that changing the amount of surface paramagnetic impurities leads to striking different relationships between the pore-size and the relaxation times T1 and T2. These relationships are well supported by fast-diffusion (surface-limited) or slow-diffusion relaxation models. Surface relaxivity parameters rho1 and rho2 are deduced from the pore size dependence in the fast-diffusion regime. Then, we evidence the frequency and temperature dependence of the surface relaxivity rho1 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 granular packings and petroleum rocks and the determination of the above mentioned surface dynamical parameters. Finally, we present the first field cycling nuclear spin relaxation experiments performed in water/oil saturated petroleum rocks. We believe that these experiments give new information about the surface localization of these two saturating liquids in pores.