| Summary: | Methane hydrates in natural geological settings are commonly distributed within sediments, with a variety of minerals (such as silica sand, talc, and montmorillonite). The mechanisms that control the influence of sediments on methane hydrate formation remain poorly understood. In this study, we performed experiments on methane hydrate formation in pure H2O with the addition of 3% sediments (montmorillonite, talc, and silica sand). A large-volume stirred reactor (80 mL) and a small-volume unstirred reactor (20 mL) were used. The results show that montmorillonite and talc severely inhibit methane hydrate formation. For experiments in the stirred reactor with pure H2O, normalized gas consumption is 30 (mmol/mol) after 1000 min. In contrast, normalized gas consumption in experiments with the addition of 3% montmorillonite and talc decreases greatly to <5 (mmol/mol) over the same period. The inhibiting effect of montmorillonite and talc is closely associated with the release of cations (Mg2+, Ca2+, K+, and Na+) into fluids, with higher concentrations of cations for slower rates of methane hydrate formation. The interaction of montmorillonite and talc with H2O consumes hydrogen ions (H+), resulting in alkaline solutions. It was found that alkaline solutions may not be favorable for methane hydrate formation. In contrast, silica sand slightly promotes methane hydrate formation in the unstirred reactor, which may be related to acidic solutions formed during the interaction of silica sand with H2O. The phase equilibrium temperatures and pressures of methane hydrate in the presence of 3% montmorillonite, talc, and silica sand are essentially the same as those in pure H2O, excluding the thermodynamic effect of minerals. The experiments of this study are important for understanding the formation of massive methane hydrates with low amounts of sediment (e.g., ≤3%). They suggest that methane hydrates may not be highly concentrated in sediments with abundant talc and montmorillonite. The experiments of this study may ...
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