Development and application of gas hydrate reservoir simulator based on depressurizing mechanism

Abstract

Natural gas hydrates are known to occur in vast quantities at the ocean floor or in permafrost regions. In-situ hydrate contains great volumes of methane gas, which indicates a potential future energy resource. In this study, we have developed a three-dimensional, multi-phase (gas, water, and hydrate) flow finite-difference model by using implicit pressure explicit saturation technique in order to investigate simultaneous flow through ice-liked hydrate reservoir. The developed model is based on the depressurizing method as producing mechanism. The model evaluates local gas generation dissociated from the hydrate with the aid of kinetic dissociation theory proposed by Kim-Bishnoi. The computation of kinetic dissociation uses the empirical dissociation rate as a function of specific surface area between phases and pressure difference. With the developed model, a one-dimensional system has been simulated for analyzing the production performance of a hydrate reservoir and for investigating the effect of hydrate saturation on absolute permeability and relative permeability characteristics. Also, for the three-dimensional field-scaled reservoir system, a number of numerical exercises have been conducted to understand the effect of mass transfer and to characterize the flowing mechanism under the conditions of increased permeability resulting from the dissociation hydrate.