Enhance Recovery of Methane from Gas Hydrate Reservoirs with CO2 sequestration

Abstract

Abstract Gas hydrates are an energy resource composed of natural gas in a solid state, in which water molecules, are in a relatively stable composition, surround the gas molecules. One volume of gas hydrates is equivalent to about 164 volumes of methane. Gas hydrates may represent more than twice the energy content of all other hydrocarbon resources. Gas hydrates are in equilibrium under conditions of high pressures and low temperatures; they occur in arctic regions (permafrost) and on the continental shelf - in marine surface and subsurface deposits. The importance of gas hydrates is related to their potential for exploration and production as a source of natural gas; to the known problems they cause in drilling and production systems; to their climate change effects - negative (GHG) and positive (CO2 sequestration). Presently, depressurization, thermal stimulation, inhibitor injection, or a combination of these methods have been considered as possible means of producing gas hydrate. Another method for gas hydrate production involves the injection of CO2. The idea of swapping CO2 for CH4 in gas hydrates was first advanced by Ohgaki et al. (1996) and then for ethane hydrate by Nakano et al. (1998). Their concept involves injecting CO2 gas, which is then allowed to equilibrate with methane hydrate along the three-phase equilibrium boundary. Because of the difference in chemical affinity for CO2 versus methane in the sI hydrate structure, the mole fraction of methane would be reduced to approximately 0.48 in the hydrate and rise to a value of 0.7 in the gas phase at equilibrium. The concept for enhanced gas hydrate recovery (EGHR) discussed in this paper takes advantage of the physical and thermodynamic properties of CO2 combined with control of multiphase flow, heat, and transport processes hydrate mass in porous media carriers.