Methane hydrate (MH) is one of the potential resources of natural gas in the near future, because it exists in marine sediments or in permafrost regions worldwide. Some extraction methods of MH from the reservoir have been proposed, such as depressurization, thermal stimulation and inhibitor injection. These are all based on the in-situ dissociation process of MH that is transformed into methane gas and water. However, there are some technical and economical problems for operation of these methods. Therefore, we have proposed a new enhanced gas recovery method by nitrogen injection. Nitrogen has the effect as an inhibitor as well as methanol and salts to shift an equilibrium condition of hydrate to high-temperature and low-pressure.
In this study, we constructed the numerical model for MH dissociation process in porous media by nitrogen injection on the basis of experimental observations. The component of gas phase was treated as a two components system consisting of methane and nitrogen, and an equilibrium condition of methane-nitrogen system was introduced into a numerical model. Through the history-matching of temperature change and gas production behavior in laboratory-scale experiments, we confirmed the validity of the constructed numerical model.
