Abstract
Abstract Efficient and robust phase equilibrium computations have become a pre-requisite for successful large scale compositional reservoir simulations. When the initial estimate of equilibrium ratios is not available from previous simulation time step, the ideal strategy for the phase-split calculation is the use of stability testing. We present a general strategy for two-and three-phase split calculations based on reliable stability testing where we apply the quasi-Newton method with superlinear convergence rate. The Wilson correlation and new correlations are combined to provide the initial estimate of equilibrium ratios. In the phase-split calculation, the successive substitution iteration (SSI), General-Dominant-Eigenvalue (GDE), and Newton methods are combined. The SSI is only first-order and is generally used to provide the initial guess for the Newton method. The GDE update is adopted to accelerate the SSI. The Newton method has quadratic convergence rate and can locate the solution within a few iteration steps when the initial guess is close enough to the solution. Powerful features of the strategy are extensively tested by calculating the complicated phase envelops of four hydrocarbon fluids mixed with CO2 in single-, two-, and three-phase regions.
Published Version
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