Date of Graduation

2013

Document Type

Dissertation/Thesis

Abstract

Natural gas hydrate reservoirs are likely to contain more carbon than in all other fossil fuel reserves combined. Different techniques currently being proposed for production of CH4 from hydrate deposits include depressurization, thermal stimulation and inhibitor injection. These processes involve the dissociation of hydrate and the release of significant volumes of water, which may cause geomechanical stress on the reservoir leading to subsidence. A series of experimental studies over the decade reviewed the feasibility of using CO2/CO2+N2 gas mixtures to recover CH4 gas from the hydrates, which serves the dual purpose of CO2 sequestration and production of CH4 while maintaining the geomechanical stability of the reservoir. The current state-of-the-art in reservoir simulators only accounts for pure CH4 hydrates, but in order to analyze a CH4 production process by injection of CO2/CO2+N2 gas mixture in gas hydrate reservoirs, a new simulation tool has to be developed to account for multi-component hydrates. In this work HydrateResSim, an open-source code available to the public through the National Energy Technology Laboratories (NETL), is modified for binary and ternary hydrates. A major component to the new code is the implementation of equilibrium surface. The equilibrium surface obtained using a cell-potential method is incorporated in to the code in tabular form and is used to interpolate data at specific conditions. Along with phase equilibrium data new primary variables are added for each phase state along with extra governing equations for newly added components. Simulations were performed to analyze the behavior of the hydrate reservoir during injection of CO2 and N2. During injection of CO2, it is found that CO2 hydrate was formed due to the available free water phase which caused a dramatic reduction in permeability of the reservoir to the injection of fluid. Therefore it is necessary to remove the free water within the vicinity of the injection well in a reservoir so as to avoid the excessive hydrate formation and blockage close to the well. In order to remove the free water before injection of CO2, the reservoir can be flooded with N2 gas. The reservoir behavior with injection of N2 is also studied and it is observed that there is ice formation near the injection well which can block the well. The solution would be to inject N2+CO2 mixture and to study the exchange process in the reservoir by injection of the mixed gas. CH4 production from a hydrate reservoir by injecting N2+CO2 (77%+23%) for 17 days, followed by depressurization is studied. It is found that during the injection period, CH4 gas is released from the hydrate while CO2/N2 gases form hydrate and during depressurization the released CH4 gas reforms hydrate while some of the CO 2/N2 gases absorbed are released. History matching for the Ignik Sikumi, first field test for gas hydrate exchange trial is conducted.

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