Study on the Dissociation Characteristics of Methane Hydrates in Porous Media above and below the Freezing Point

Natural gas hydrates are crystalline structures formed by the combination of water and natural gas under specific temperature and pressure conditions. They hold tremendous potential as a viable alternative energy source. However, the field of natural gas hydrates faces widespread challenges, including low gas production rates and uneven gas production. In order to achieve low-enthalpy and sustainable methane hydrate production, this study conducted methane hydrate sample reshaping within sediments with varying initial water saturation levels. The research investigated the gas production behavior of methane hydrates within sediments characterized by different initial water saturation under varying production temperatures. Additionally, it employed a no-solid-phase dissociation technique to study the gas production behavior of methane hydrates within sediments at temperatures below the freezing point. The results indicate that, compared to the dissociation process of hydrates above the freezing point, the gas production behavior of hydrate reservoirs at a dissociation temperature of 272.15 K exhibits a delayed response with prolonged slow dissociation times. Lower temperatures are advantageous for sustaining gas production rates. Notably, the no-solid-phase dissociation method exhibits significant superiority, particularly in high water saturation reservoirs. Within high water saturation reservoirs, methane hydrates at 272.15 K exhibit an increased dissociation rate, rising from 68% at 278.15 K to 78%. In the case of hydrates below the freezing point, the controlling step for no-solid-phase dissociation is identified as the gas diffusion process. This method effectively mitigates the hindrance imposed by the water layer on gas diffusion, ensuring enhanced mass transfer efficiency.