| Summary: | Gas Hydrates (GHs) are naturally occurring solid, crystalline compounds in which natural gas is trapped inside the cage like structures formed by water molecules. Lately a novel technology has been developed for the production of methane from in-situ GHs by injection of CO2. Addition of N2 to CO2 for hydrate production has an advantage of both higher methane recovery and CO2 sequestration. Injected CO2/N2 mixture into in-situ methane hydrate replaces the CH4 molecules in the hydrate cage and form new CO2 dominated CO2 hydrate or mixed CO2-CH4 hydrate. This conversion is based on two primary mechanisms; first is through formation of new hydrate and second is direct solid state exchange. The main goal of this master thesis is to study the feasibility of CO2-N2 gas mixture injection method in methane recovery. In pursuit of this goal hydrate stability limits for different mixtures of CO2/N2 in terms of chemical potentials as function of gradual decrease in CO2 content in gas mixture have been evaluated. The CO2:N2 ratio is a sensitive balance. Nitrogen concentration applied in relevant simulations carried out in this thesis vary from 30% to 80%. Residual thermodynamics has been applied for all the components in all phases as a basis of free energy analysis of hydrate stability in order to have same reference level of chemical potentials for all components in all phases. The kinetics of hydrate phase transition in porous media is implicit function of mass-transport dynamics, heat transport dynamics and the kinetics of the phase transition itself. The work presented in this thesis is a contribution to the description of the thermodynamic forces related to the phase transition kinetics. A natural extension of this work would be the inclusion into a hydrate reservoir simulator in order to complete the couplings to mass and heat-transport. For this reason, as a service to external researchers that might want to incorporate these models into their simulator, a fairly detailed description of the thermodynamic models is ...
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