FEATURES OF DECOMPOSITION OF GAS HYDRATE IN NONEQUILIBRIUM MODE IN A POROUS MEDIUM

Abstract

The paper presents a mathematical model of the nonequilibrium decomposition of a gas hydrate contained in a porous reservoir of finite extent. The system of basic equations, which includes the law of conservation of mass, the heat inflow equation and Darcy’s law, also contains an equation describing the kinetics of nonequilibrium hydrate decomposition, which is determined by pressure, temperature and surface area of particles. On the basis of the numerical solution of the problem, dependences are obtained that allow us to identify the regularities of the process of nonequilibrium decomposition of gas hydrate in a natural reservoir when warm gas is injected into a porous reservoir. It is shown that at the initial moments of time after the start of injection, the extent of the region saturated with gas, hydrate and water is very small compared to the extent of the formation, which corresponds to the mode of hydrate decomposition on the frontal surface. At long injection times, the nonequilibrium hydrate decomposition process is characterized by the formation of three characteristic zones: the near one, where the pores are saturated with gas and water, the far one, saturated with methane and its gas hydrate, and the intermediate one, where gas, hydrate and water are located. It is established that the pressure and temperature in the extended region are connected by the condition of phase equilibrium. The influence of the main parameters of the system on the distributions of pressure, temperature, water saturation and hydrate saturation, as well as on the dynamics of their changes over time, is analyzed. It is shown that injection pressure, as well as reservoir permeability and porosity have a significant effect on the decomposition rate of gas hydrate. An increase in the values of these parameters contributes to an increase in the rate of nonequilibrium hydrate decomposition. An increase in the injection temperature leads only to an increase in the extent of the area containing methane and water.