Phase Equilibria of Methane Hydrate in Various Mineral Systems in the Haima Cold Seep Area

Methane hydrates are widely present in sediments in the Haima cold seep area, but the effect of the complex sediment components on the phase equilibrium of methane hydrates is not comprehensively understood. In this work, six minerals with high contents were selected from sediments collected from the Haima cold seep: illite, chlorite, quartz sand, calcite, potassium feldspar, and albite. The methane hydrate phase equilibria for these minerals were measured at 285–289 K. The results showed that potassium feldspar and albite had thermodynamic promoting effects on the formation of methane hydrate, which could be attributed to the participation of the feldspar surface structure in the formation of the gas hydrate lattice, promoting the establishment of hydrate cages. This is a newly discovered mineral effect that influences the phase equilibrium of methane hydrate. Compared with the pure water system at the same pressure, the phase equilibrium temperatures of methane hydrate in the K-feldspar and albite systems with 30% water saturation were 0.3 and 0.2 K higher, respectively. Both illite and chlorite inhibited the formation of methane hydrate, with the inhibitory effect of illite being stronger than that of chlorite. Quartz sand and calcite had little effect on the phase equilibria of methane hydrate. These findings provide a basis for determining the occurrence range of methane hydrates and evaluating the methane hydrate content in the Haima cold seep area.