Abstract
Depressurization is regarded as the most effective process for gas recovery method from the viewpoints of gas productivity and economical efficiency, compared with the other in-situ dissociation processes of Methane Hydrate (MH) . It is necessary to develop a numerical simulator for the prediction of the gas productivity from MH reservoirs. We are currently developing a numerical simulator in which the thermal conduction, the mechanical behavior of MH sediments and the fluid migration in porous media are analytically coupled. In this study, we conducted numerical studies on laboratory-scale experiments for MH dissociation process in porous media by depressurization using the numerical simulator. In the numerical model, the distribution model was used for the thermal conductivity of MH sediment. In order to evaluate the deformation behavior of the MH sediment, the elastic model for MH sediment, which was constructed on the basis of experimental results, was newly introduced into the numerical model. Using the modified numerical model, we carried out history matching for temperature change, deformation behavior and gas and water production during depressurization experiments. The change in the temperature in the MH sediment during dissociation was reproduced considering the hydrate-saturation distribution. The deformation behavior of the MH sediment was reproduced using a value for Poisson's ratio of MH sediment according to the kind of soil. The gas-water production behavior was reproduced, optimizing the shapes of the relative permeability curves that allowed us to reproduce the fluid migration in the MH sediment. To consider the effect of capillary pressure on gas-water multi-phase flow condition, we extended linear relative permeability model by introducing indexes. From the results of history matching, it was found that the modified numerical model could reproduce the series of behaviors during depressurization.
