Compositional reservoir simulations require a huge number of flash calculations. The problem dimensionality (and thus the computational effort) is usually reduced by lumping several (often many) individual components into pseudo-components. Typically, less than 10 pseudo-components are used for full-scale field simulations. However, the detailed fluid phase split is important for surface process simulations. The detailed phase compositions resulting

A possibility for reducing the dimensionality of the phase equilibrium problem is given by the reduction method. The number of independent variables for reduced phase equilibrium calculations is independent of the number of components in the mixture. For two-phase flash calculations, the number of independent variables is m + 2, where m is the number of non-zero (or non-negligible) eigenvalues of the matrix with (1 - kij) elements (kij denotes the

In this work we propose a new reduction method for phase equilibrium calculations using a general form of cubic equations of state (CEOS). The energy term in the CEOS is a quadratic form, which is diagonalized by applying a linear transformation. The number of the reduction parameters is related to the rank of the matrix C with elements (1-Cij), where Cij denotes the binary interaction parameters (BIPs). The dimensionality of the problem depends

Simulation of improved recovery processes from gas condensate and volatile oil reservoirs is significantly affected by the match of experimental PVT data. Therefore, a proper characterization of the mixture composition and tuning of the equation of state used are crucial for the accuracy of the reservoir model. This paper presents an efficient method for phase behaviour matching by non-linear regression. The constraints introduced by the boundaries

A simple method is proposed for the calculation of any type of P-T curve for the most general case of two-parameter equations of state in the single-phase area. For each component parameter, temperature dependency can be expressed on the basis of any analytical function; for the mixture, any mixing rule can be considered for any parameter. For the construction of these curves, the numerical algorithm is completely described. This method is illustrated

A new and efficient method for phase equilibrium calculations using cubic equations of state (EOS) has been developed. The reduced flash technique presented here takes into account non-zero binary interaction coefficients (BIC's), and requires the iterative correction of a reduced number of independent variables (2m+3, where m is the number of components with non-zero BIC's), irrespective of the number of components in the mixture. A new extrapolation

In this paper, we propose a new method for phase stability analysis with cubic equations of state by minimization of the tangent plane distance (TPD) function. A global optimization method called tunneling, able to escape from local minima and saddle points is used here. The tunneling method has two phases. In phase one, a local bounded optimization method is used to minimize the TPD function. In phase two (tunneling), either global optimality is

This paper presents a new method for multiphase equilibria calculation by direct minimization of the Gibbs free energy of multicomponent systems. The methods for multiphase equilibria calculation based on the equality of chemical potentials cannot guarantee the convergence to the correct solution since the problem is non-convex (with several local minima), and they can find only one for a given initial guess. The global optimization methods currently

Wax precipitation for gas condensate fluids was studied in detail with a thermodynamic model. It was found that the precipitated wax phase can exhibit retrograde phenomena similar to that in gas condensates. As a result of pressure decrease (at a constant temperature), the amount of precipitated wax may first increase, then decrease. then increase again. The effect of pressure on wax precipitation from gas condensates was also studied. Pressure often

In this study we propose a method for phase stability analysis at pressure and temperature specifications, in the frame of a “volume-based” thermodynamics. The formulation of the tangent plane distance (TPD) criterion in terms of the Helmholtz free energy is used in this work for testing phase thermodynamic stability at p-T conditions, using component molar densities as primary variables. The phase stability problem is non-convex; the TPD function