NMR Relaxation Response of CO2 Hydrate Formation and Dissociation in Sand

Quantification and characterization of hydrate formation and dissociation in sediments are highly important in the study of the physical properties of hydrate-bearing sediments. In this paper, the behavior of CO2 hydrate formation and dissociation in sand is studied using the nuclear magnetic resonance (NMR) technique. The components of the pore space, including gas, liquid water, and hydrate, were quantified using a convenient method by which the hydration number was determined. No abrupt change in the relaxation behavior of the sample was found during hydrate formation and dissociation. In addition, the value of mean-log T-2 appeared to be proportional to the liquid water content of the sample with or without the pore hydrate. A straightforward explanation is that the liquid water in the pore space remains in contact with grain surfaces, and relaxation occurs mainly at the grain surface. The results suggest that, rather than coating the grains, the hydrate is pore-filling or cementing.