Mathematical model of injection of liquid carbon dioxide in a reservoir saturated with methane and its hydrate

Abstract

Based on the equations of mechanics of multiphase media, a mathematical model of the injection of liquid carbon dioxide into a natural reservoir saturated with methane and its gas hydrate is constructed. Numerical solutions for two different flow regimes are obtained and investigated. In the first regime, methane is replaced by carbon dioxide in the gas hydrate without the release of free water. In the second mode, gas hydrate decomposes into methane and water, and further formation of CO2 gas hydrate from water and carbon dioxide occurs. Numerical calculations show that the first mode is realized at low values of permeability and injection pressure, as well as high values of the temperatures of injected carbon dioxide, initial temperature of the reservoir and pressure at the right boundary of the reservoir. For each regime, the conditions under which the pressure in the liquid carbon dioxide filtration region can drop below the equilibrium boiling point of CO2 are investigated. Numerical calculations show that this is possible at low injection pressures and pressures at the right boundary of the reservoir. Critical diagrams were constructed that determine the “injection pressure-pressure on the right-hand boundary of the reservoir”, “injection pressure-permeability”, “injection pressure-injection temperature” and “injection pressure-initial temperature of the reservoir” in the region of existence of four qualitatively different flow regimes.