It is critical to probe in situ the dynamics and wettability of oil, water, and gas trapped in the complex microstructure of oil-shale rocks. However, usual techniques cannot separate these fluids in shale rocks. Here, we use multifrequency and multidimensional nuclear magnetic relaxation (NMR) techniques for probing these dynamics. The frequency dispersion behaviors of the longitudinal relaxation rates 1/T 1 for oil and water confined in shales are interpreted through a relaxation model showing one-dimensional (oil) and two-dimensional (2D) (water) diffusing phases confined within the organic kerogen and mineral layers, respectively. We probe the average hopping and residence times of these fluids at pore surfaces and assign signals to water and oil at both organic and mineral pore surfaces for characterizing their local wettability. This allows interpreting our 2D T 1 −T 2 correlation spectra that could be made down-hole, thus giving an invaluable tool for investigating oil and gas recovery on these important porous rocks.

We propose using a set of noninvasive multiscale NMR techniques for probing the structure and dynamics of bulk and confined crude oils with and without asphaltene. High-field 1D (1)H and (13)C NMR spectroscopies evidence the proton species and the amount of asphaltene and give an average chain length for the hydrocarbon aliphatic chains. Two-dimensional (1)H diffusion-ordered NMR spectroscopy (DOSY) spectra allow us to identify two populations of hydrocarbons characterized by two distributions of translational diffusion coefficients in the presence of asphaltene and a single one without asphaltene. A detailed analysis of the distributions of longitudinal, T1, relaxation times measured at different magnetic fields is proposed in terms of highly skewed bimodal (or monomodal) log-normal distributions, confirming the two environments in the presence of asphaltene and a single one without asphaltene. We show that these distributions are similar to the gas and gel permeation chromatography distributions, thus showing a connection of the hydrocarbon dynamics with their chain lengths. The remarkable observed features of the nuclear magnetic relaxation dispersion (NMRD) profiles of <1/T1> for bulk and confined crude oils with and without asphaltene are interpreted with an original relaxation model of intermittent surface dynamics of proton species at the proximity of asphaltene nanoaggregates and bulk dynamics in between clusters of these nanoaggregates. This allows us to probe the 2D translational diffusion correlation time and the time of residence of hydrocarbons in the proximity of the asphaltene nanoaggregates. Provided that the diffusion of the hydrocarbons close to the asphaltene nanoaggregates is three times smaller than the bulk diffusion, as the DOSY experiments show, this time of residence gives an average radius of exploration for the 2D hydrocarbon diffusion, r2D ≈ 3.9 nm, of the same order of magnitude as the aggregate sizes found by J. Eyssautier with SAXS and SANS in asphaltene solutions and by O. C. Mullins with the observation of gravitational gradients of asphaltenes in oilfield reservoirs.