Formation of methane hydrate from water sorbed by anthracite: An investgation by low-field NMR relaxation

Typical T2 spectra and their changes with time for the wet coal sample in which methane hydrate was obtained. [Display omitted] •T2 spectra were studied for the coal samples in which methane hydrate was obtained.•Partial replacement of water from coal mesopores into larger pores occurred.•Previously proposed multistage model of hydrate formation in coal was confirmed. Transverse relaxation time spectra T2 were studied for the samples (a) of wet coal in which methane hydrate was obtained, (b) wet coal exposed under the pressure of methane without the formation of the hydrate, and (c) initial wet coal. In all these cases, the samples of wet coal contained only water adsorbed in the fine pores of the coal substance. It was demonstrated that hydrate formation and the competitive sorption of methane at the positions previously occupied by water causes replacement of a part of water from coal mesopores into larger pores. The data obtained confirm a previously proposed multistage model (Smirnov et al., 2018) of hydrate formation in natural coal, which includes the stages of replacement of a part of sorbed water from coal pores by gas, the formation of microscopic water fragments in larger coal pores, and the formation of hydrate from this water.