Experimental Study on the Decomposition Characteristics of Methane Hydrate for the Pressure Regulation of Production Processes

Methane hydrate is a promising energy source to alleviate the tight energy demand worldwide. The pressure regulation during the production process of hydrate deposits by the economical depressurization method still lacks experimental simulations. In this study, four targeted production pressures (2.3, 2.5, 2.7, and 2.9 MPa) with three rated gas production fluxes (0.18, 0.30, and 0.58 Ls/min) were employed to investigate the methane hydrate decomposition during the pressure regulation process. The increase in gas flux is positive for both the depressurization and hydrate decomposition rates. A stationary state in non-equilibrium thermodynamics is obviously and universally observed in all cases when the deposit pressure-temperature is in a synergistic relationship and the decomposition rate of hydrates is time-invariant. Before the stationary state, a dynamic competition between pressure drop and hydrate decomposition under a rated gas flux is found. During the stationary state, the decomposition rate is linearly related to the corresponding depressurization rate under different rated gas fluxes, revealing the improvement of pressure drop (rather than pressure itself) on hydrate decomposition by enlarging the driving force. Hence, the optimal production process of hydrates should be based on dynamic depressurization considering the rated gas flux of production pipelines. The findings provide direct guidance for the pressure regulation method of hydrate production.

Automated summary

This study investigates the pressure regulation process of methane hydrate production and finds that the decomposition rate of methane hydrates is time-invariant and shows a non-equilibrium state under pressure-temperature conditions. The results demonstrate the positive effects of dynamic depressurization and gas flux on the decomposition rate of methane hydrates, and reveal that increasing the depressurization rate is more effective than increasing the pressure itself in promoting hydrate decomposition.