Numerical simulation of condensing gas drive
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1975
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This study describes the development and application of a two dimensional numerical model capable of simulating condensing gas drives of undersaturated oil reservoirs. The mathematical formulation is done by the finite difference method and is a modification of a conventional beta-type, fully implicit, gas-oil model with simultaneous solution of pressures and saturations by matrix inversion. Coupling of gas and oil mobilities eliminates the abrupt pressure changes that otherwise occur if fully upstream mobilities are used when the gas front breaks into a new grid block. Interphase mass transfer from the rich gas to the undersaturated oil is handled by the use of modified Buckley-Leverett theory incorporated in the model. Numerical dispersion is avoided by implicitly tracking the position of the gas front within a grid block. Phase equilibrium between gas and oil is thereby obtained in only that fraction of a grid block that has been contacted by gas. Results from the computer runs demonstrate the effects of injection rate, dip angle, and solubility on sweep efficiency and oil recovery. It is observed that the averaging of mobilities gives more correct pressure profiles than when using upstream mobilities as the front moves through the system and that the saturation profile at breakthrough in a one-dimensional system checks with the Buckley-Leverett theory.
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Major petroleum engineering