Theoretical studies of Methane Hydrate Dissociation in porous media using RetrasoCodeBright simulator

Abstract

Methane hydrates in reservoir are generally not in chemical equilibrium, there may be several competing hydrate phase transitions like for instance hydrate dissociation due to pressure or temperature changes, hydrate reformation, hydrate dissociation due to contact with under saturated fluids and mineral surfaces. The limited numbers of reservoir simulators, which have incorporated hydrate, are normally simplified by considering only pressure and temperature as criteria for hydrate stability region. If kinetic description is used it is very oversimplified and usually extracted from models derived from experiments in pressure, temperature volume controlled laboratory cells. Reservoir scale simulation of hydrate dynamics are important investigations, which enable engineers to predict the production potential of a methane hydrate reservoir and propose efficient production scenarios. Several research groups have been recently working on this subject but there seems to be significant differences in their approaches and results. In this work a reactive transport reservoir simulator, namely Retraso CodeBright (RCB), has been modified to account for hydrate kinetic phase transitions in the reservoir. For this purpose, hydrate has been added as a pseudo-mineral component and advanced kinetic models of hydrate phase transitions have been developed. The main tools for generating these models have been phase field theory simulations, with thermodynamic properties derived from molecular modelling. The detailed results from these types of simulations provides information on the relative impact of mass transport, heat transport and thermodynamics of the phase transition which enable qualified simplifications for implementation into RCB. The primary step was to study dissociation of methane hydrate under depressurization condition with a certain kinetic rate on a model inspired based on real methane reservoir. Messoyakha methane hydrate reservoir from East Siberia was chosen for constructing model for this theoretical study. Details of the simulator, and numerical algorithms, are discussed in detail and some relevant examples are shown.