Study on the mechanism of decomposition of methane hydrate by the compound inhibitor

Gas hydrate plugs, slow dissociation rates, and low production have long posed significant challenges to the commercial viability of gas hydrate extraction. This study investigated the inhibitory effects of ethylene glycol (EG), EG + polyvinyl pyrrolidone (PVP), and EG + PVP + sodium chloride (NaCl) on the dissociation characteristics of methane hydrate through molecular dynamics simulations and experiment. Simulation results indicate that the hydroxyl groups in ethylene glycol (EG) molecules and chloride ions of sodium chloride (NaCl) can effectively form hydrogen bonds with the water molecules in the hydrate and disrupt the cage structure of the methane hydrate, accelerating the dissociation of the hydrate. Meanwhile, the hydrocarbon chains in polyvinylpyrrolidone (PVP) molecules adsorb methane molecules, occupying the active space and significantly inhibiting the hydrate dissociation. The EG + NaCl exhibits a significantly higher dissociation efficiency compared to other inhibitor combinations, because of the highest first peak of the C-C radial distribution function and the lowest first peak of the C-O radial distribution function. Additionally, both the MSD slope and the diffusion coefficient are greatly increased, indicating enhanced dissociation and diffusion behaviors. Experimental results indicate that with 20% EG + 10wt% NaCl solution, hydrate sample will be completely dissociated within 300 min. The dissociation efficiency is significantly better than that of other combinations. The reagent combination of 20% EG + 10wt % NaCl is recommended to effectively improve the efficiency of natural gas pipeline cleaning and hydrate resource development.