Effects of temperature holding on methane hydrate decomposition process by thermal stimulation

Abstract

Methane hydrate is an important clean energy source. In this study, the decomposition curve of methane hydrate in the thermal stimulation process with the heating rate of (0.9, 1.8, and 2.7) K·min−1 is found and summarized. When the temperature holding process occurs during the thermal stimulation process, the hydrate decomposition cannot be stopped immediately. The pressure of the reactor deviates from the thermal decomposition curve of methane hydrate without temperature holding process due to the impact of temperature fluctuation. It was found that when the holding temperature increased from 277.56 K to 281.15 K at the heating rate of 1.8 K·min−1, the maximum temperature fluctuation increased from 0.46 K to 1.25 K. Thus, the decomposition pressure of methane hydrate with a temperature holding process is higher than that of methane hydrate without a temperature holding process. After the temperature fluctuation process, the methane hydrate equilibrium curve under the equilibrium state reached by the hydrate at the holding temperature is summarized. When the temperature holding process is over, the temperature of the reactor continues to rise, leading to the decomposition of methane hydrate. The heat in the reactor is slowly transferred again. Then, the methane hydrate decomposition curve with and without temperature holding process coincide. It was found that when the holding temperature increases from 277.56 K to 281.15 K at the heating rate of 1.8 K·min−1, the percentage of pressure difference between the equilibrium curve and the decomposition curve of methane hydrate increases from 4.34% to 8.81%. The initial heating temperature and heating step have no effect on the decomposition characteristics of methane hydrate with a temperature holding process. The heating rates can affect the slope of the hydrate decomposition curve. This study is of great significance for the safe application of methane hydrate thermal stimulation process.