Simulations of Underground Storage of Natural Gas
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The purpose of this thesis is to simulate fluid flows in aquifers used for natural gas storage. An introduction is given to aquifer flow modelling, and two models are developed that describe two-phase flow in porous media. The first model is constructed using the standard equations for Darcy flow and conservation of mass. The second model is then developed by integrating these equations in the vertical direction, and using the assumption of a sharp-interface and vertical equilibrium to evaluate the integrals. These two models were tested by running simulations on the aquifer model of Stenlille, a major gas storage facility in Denmark. The specifics of the aquifer model, such as the grid, fluid properties and so on, were based upon an existing ECLIPSE model. The goal was to improve the capability the simulations had in predicting pressures and water production rates for the wells in the aquifer. To this end, the ECLIPSE model of the aquifer was transferred into the MRST framework, where it was easier to experiment with the models themselves. The simulations run in MRST, using both the black-oil model and the VE model, were found to give successful predictions of the well pressures. As the VE model is two-dimensional, run-times were significantly lowered when this model was utilized. Neither the simulations run in MRST nor ECLIPSE were found to give successful predictions of water production rates.