Archive | 2019
A NMR-based analysis of carbon dioxide hydrate dissociation process in silt
Abstract
It is necessary to determine the equilibrium condition and dissociation process of natural gas hydrate in porous media in the evaluation and recovery of natural gas hydrate as an energy resource. Based on the NMR technique, the liquid water content and distribution during hydrate dissociation process in the silt were detected and the hydrate saturations were calculated. The results showed that the hydrate in the small pores dissociated first as the increase of temperature, and then the hydrate in the macropores began to dissociate. Since the surface relaxivity of sample kept unchanged during the hydrate dissociation process, it was inferred that the hydrate cannot coat soil particles and hydrate grown in the middle of pore. The phase equilibrium condition of carbon dioxide hydrate in silt was a curve in P - T - S h space, which indicated the specific experimental path. Variation of T 2 distribution curves of silt before and after hydrate formation/dissociation verified the microstructure alteration during the test and small pores decreased and correspondingly large pores increased. As the temperature increased to 4°C, hydrate saturation decreased with carbon dioxide consumption, which indicated that hydrate number decreased during hydrate dissociation process.