Numerical study for production performances of a methane hydrate reservoir stimulated by inhibitor injection

Abstract

This study presents a numerical model for simultaneous flow of gas, water including methanol, and hydrate through methane hydrate reservoirs. The model has been developed to specially investigate the production behavior during injection of methanol with the combination of a depressurization mechanism. The model evaluates the local gas dissociation rate with methanol concentration using the kinetic theory proposed by Kim-Bishinoi and thermodynamics. This kinetic dissociation rate is computed with the aid of the empirical dissociation rate as a function of specific surface area and pressure difference. A number of simulations have been conducted to examine the effect of parameters related to methanol injection on the production behaviors of gas and water, that is, injection rate, time of injection, and methanol content. From the results of numerical studies, it is noted that the effect of methanol injection only appears near the well, rather than whole reservoir since hydrate reservoirs are extremely low in permeability before dissociation occurs. Front the parametric study, it is seen that methanol content is the most sensitive parameter in a sense of time being taken for a well block to be completely dissociated. We also investigated the strategy of injecting methanol in the middle of production. It was found that this strategy is not much expected in the aspect of areal sweeping trend, The results obtained from this model can be used to acquire the relevant reservoir data, to interpret the observed producing behavior; and to design the production scenarios for economical evaluation.