2018 Volume 83 Issue 6 Pages 461-472
In this study, for the purpose of enhanced gas recovery from an methane hydrate （MH） reservoir, we conducted experimental and numerical study for acid injection process as a secondary gas recovery after the depressurization operation. This process is based on the concept of effective utilization of heat generation resulting from mineral dissolution via acid injection for the promotion of in-situ dissociation of MH. For the numerical analysis for the acid injection process, based on the assumption that the charge balance in the injected acidic solution after the contact with the solid matrix becomes neutral due to mineral dissolution into the water phase, we defined two acid components before/after the contact with the solid matrix. In addition, the kinetic parameters and heat of mineral dissolution during the acid injection were obtained through laboratory column tests and DSC analysis, respectively, and introduced into the developed numerical model. Using this numerical model, we conducted a series of numerical analyses for the acid injection process after the depressurization operation. From the calculation results, it was found that a high-temperature zone formed by in-situ heat generation resulting from mineral dissolution extended to the side of the production well to promote MH dissociation. Based on the total amount of methane gas trapped in MH at the initial stage, total gas recovery using depressurization and acid injection was estimated to be approximately 90% and we confirmed that the acid injection process is very effective as a secondary gas recovery targeting the MH reservoir under low-temperature and low-pressure condition after the depressurization operation.
