Numerical study on enhanced gas recovery from methane hydrate reservoir during in-situ heating process by acid injection

In this study, under the concept of effective utilization of heat generation resulting from mineral dissolution via acid injection for the promotion of in-situ dissociation of methane hydrate (MH) and the enhancement of gas recovery, we conducted a series of numerical analyses of the acid injection process as a secondary gas recovery from an MH reservoir after the depressurization operation. For the numerical analysis, based on the assumption that the charge balance in the injected acid solution after the contact with the solid matrix becomes neutral as a result of mineral dissolution into the water phase, two acid components before and after the contact with the solid matrix were defined. In addition, the kinetic parameters and heat of mineral dissolution during the acid injection were obtained through laboratory column tests and differential scanning calorimetry (DSC) analysis, respectively, and introduced into the developed numerical model. From the calculation results, it was found that the high-temperature zone formed because of heat generation resulting from mineral dissolution extended to the side of the production well promoting MH dissociation, and the total gas recovery through depressurization and acid injection was estimated at approximately 90%.