Experimental Analysis on Thermodynamic and Kinetic Characteristics of Water‐Saturated Natural Gas Hydrates by Depressurization Decomposition

Abstract

Natural gas hydrate has attracted worldwide attention for its abundant availability and clean and nonpolluting combustion products. The actual environment of marine methane hydrates is water‐saturated, but present researches on water‐saturated hydrates are relatively few. This study prepares water‐saturated hydrate sediment of ≈70% saturation and mainly focuses on the thermodynamic and kinetic characteristics of decomposition process using different depressurization rates. Compared with gas‐saturated hydrates, both the thermodynamic evolution and the decomposition kinetics of water‐saturated hydrates get weakened due to the inhibition of water molecules surrounding hydrate crystals on heat and mass transfer. In all experimental cases of water‐saturated hydrates, the temperature still decreases at most 0.5 °C in several minutes after the pressure has become constant, indicating the delay effect of depressurization in water phase. The results show that the increase in depressurization rate strengthens both temperature decrease and pressure delay of water‐saturated hydrate‐bearing sediment. In addition, the decomposition rate of water‐saturated hydrates in depressurization stage is constant and positive to the depressurization rate, while the decomposition rate in constant pressure stage is a function of residual hydrate amount. This study is significant for decomposition control of hydrate mining under actual marine environment.