Simulation Study on Injection of CO₂-Microemulsion for Methane Recovery From Gas-Hydrate Reservoirs

Gas-hydrates are crystalline substances composed of water and gas, mainly methane, in which a solid water lattice accommodates gas molecules in a cage like structure. Large methane-gas hydrate reservoirs have been found on the North Slope of Alaska that can be exploited as a future energy source. Depressurization, thermal stimulation, and inhibitor injection are the methods being evaluated for commercial production of natural gas from hydrate-bearing geologic formations.

An alternative method of gas hydrate production using CO₂ is under investigation. This process conducts injection of CO₂ in the form of microemulsion. This concept has several attractive features: 1) CO₂ is thermodynamically favored over CH₄ in hydrate, 2) the heat released by formation of CO₂ hydrate is 20% greater than the heat needed for dissociation of CH₄ hydrate, 3) refilling pore space with CO₂ hydrate is expected to maintain mechanical stability of the hydrate-bearing formations during production, and 4) the process is environmental friendly, removing CO₂ from the atmosphere while simultaneously producing clean-burning natural gas. This study focuses on the evaluation of a set of optimum parameters for methane recovery with simultaneous CO₂ sequestration using the STOMP-HYD simulator. Series of simulations are being carried out to verify the effect of pressure, temperature, CO₂-microemulsion injection rate, and the concentration of injected CO₂-microemulsion on methane hydrate dissociation. Preliminary, 1-D simulations show that injection of CO₂-microemulsion produces considerably more amount of methane than warm water injection alone. These results have also demonstrated that injection of liquid CO₂-microemulsion helps in early and significant methane production as compared to the injection of vapor CO₂-microemulsion. Initial modeling work supports the novel idea of using CO₂-microemulsion for Enhanced Gas Hydrate Recovery.