NUMERICAL STUDY OF THE STEAM INJECTION PROCESS INTO A FORMATION CONTAINING METHANE GAS HYDRATE

In this paper, a mathematical model of superheated steam injection into a porous reservoir initially saturated with methane and its hydrate is presented in a plane-dimensional approximation. The model is based on the assumption that four regions are formed in the formation, saturated with superheated steam, methane and its hydrate, as well as containing products of steam condensation (water) and hydrate decomposition (methane and water). At the same time, the model also takes into account the formation of three movable boundaries separating the above-mentioned areas and on which the laws of conservation of mass and energy are fulfilled. The system of basic equations describing steam injection into a methane hydrate reservoir consists of mass conservation equations (for methane and steam), heat inflow and Darcy's law. It should be noted that methane and steam are considered as calorically perfect gases, and water is stationary, which is explained by the small value of the initial hydrate saturation. Based on the results of numerical experiments, pressure and temperature distributions are constructed, which are realized during the injection of steam into a porous formation. It is shown that the main pressure and temperature drop in a porous reservoir is realized in the areas of steam and condensed water filtration. The laws of motion of the movable boundaries of phase transitions for different values of the parameters of the porous skeleton and the injected steam are established. It is shown that the parameters of steam injection and a porous medium significantly affect only the extent of the region containing condensed water in the pores, as well as the coordinate of the contact boundary and its temperature. It is shown that with an increase in the values of injection pressure and reservoir permeability, as well as a decrease in the initial pressure of the system, the extent of the region containing condensed water increases, and the region containing decomposition products of gas hydrate, on the contrary, decreases. It has been established that the temperature at the contact boundary at high permeability values is close to the hydrate decomposition temperature, and at low values – to the vapor condensation temperature.