Известия Томского политехнического университета: Инжиниринг георесурсов (Feb 2018)
Injection of carbon dioxide in gas hydrate porous reservoir
Abstract
The relevance of the research is associated with a new approach to natural gas extraction from the gas hydrate reservoir, which has a number of advantages over the previous methods. In the previously described methods, warm water was injected or pressure was lowered. This leads to high energy costs, the release of associated products (water and sand) and destruction bottom of the sea. The methane carbon dioxide substitution method considered in this paper does not have these drawbacks and can be considered as a method for conservation of carbon dioxide. The main aim is to study the features of methane replacement by carbon dioxide in gas hydrate formation during carbon dioxide injection in a porous reservoir; to carry out a numerical experiment for determining the influence of the system main parameters on pressure and temperature of the reservoir. Objects: gas hydrate reservoir of finite length, pressure and temperature of which at the initial moment of time correspond to the conditions for the stable existence of the gas hydrate. Methods. The authors have constructed a mathematical model for methane replacement by carbon dioxide in gas hydrate, taking into account the finite extent of the formation. To describe the processes of heat and mass transfer in a porous medium, a system of equations is used, including the laws of conservation of masses, energy, Darcy's law, the equation of state. Research results. The authors have constructed the mathematical model for injecting carbon dioxide into the reservoir saturated with methane and its hydrate. The numerical experiment showed that in a certain range of parameters characterizing the injected gas and the initial state of the formation, the obtained reservoir temperature in the region saturated with methane gas hydrate is below the equilibrium decomposition temperature of methane gas hydrate, which corresponds to the calculated pressure distribution. When the pressure of the injected carbon dioxide decreases or the formation pressure increases, the formation temperature rises above the equilibrium decomposition temperature of the methane hydrate. Therefore, it is necessary to introduce a second boundary of phase transitions and, accordingly, an intermediate region saturated with methane and water.
