Numerical investigation of the methane hydrate decomposition in the process of warm gas injection into a hydrate-saturated reservoir

Currently, natural reservoirs of the gas hydrates represent a serious alternative to the conventional sources of the natural gas due to a significant amount of hydrates and concentrated state of gas in them. The main methods for methane extraction from such reservoirs are the pressure reduction, heating hydrate-containing rocks, injecting carbon dioxide into the bed, injecting organic or saline solutions contributing to a gas hydrates' decomposition. A mathematical model in a flat-radial approximation is proposed in the paper, and the properties of warm gas (methane), whose temperature is higher than that of bed at the initial state, injecting into a natural stratum initially saturated with methane and its hydrate are investigated. The developed mathematical model considers the main physical particularities of a thermal effect on the hydrate-saturated reservoir, such as non-isothermal gas filtration, gas hydrate decomposition, real gas properties, adiabatic cooling effects, and the Joule–Thomson effect. The numerical solution to a one-dimensional problem describing distributions of the main parameters in the reservoir is obtained. An influence of the injected gas parameters and initial hydrate saturation of the bed on the intensity of methane hydrate decomposition is studied. It is shown that the gas hydrate decomposition during the process of a warm gas injection into the hydrate-saturated reservoir is characterized by a frontal mode of phase transitions.