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Abstract

Phase behavior modeling of a reservoir Phase behavior modeling of a reservoir hydrocarbon mixture through an equation-of-state, EOS, is preceded by the adjustment of some of the preceded by the adjustment of some of the parameters in the equation so as to reproduce measured parameters in the equation so as to reproduce measured PVT data of the mixture. In this paper we PVT data of the mixture. In this paper we propose a methodology for the automatic fitting of propose a methodology for the automatic fitting of EOS parameters for phase behavior matching.

Critical properties of the heaviest, C+, fraction are obtained from available correlations and fit ting of EOS parameters, Omega and Omega, for CH4 and C+ as well as of the binary interaction coefficient, delta CH4 - C+, are performed according to the following procedure: First, keeping the theoretical values of procedure: First, keeping the theoretical values of Omega and Omega we calculate the interaction coefficient sigma CH4 - C+ that matches the saturation pressure of the mixture. In a second step, the parameters Omega and Omega for the CH4 and C+ fractions are fitted through a non-linear least squares regression technique to match PVT experimental data in the one-please region. Peculiarities of the system of equations produced by the fitting algorithm are discussed; proper solution techniques are discussed as well.

The above procedure was used to adjust the PengRobinson EOS to four reservoir hydrocarbon fluid PengRobinson EOS to four reservoir hydrocarbon fluid samples, which include gas condensate. Phase behavior in the two phase region predicted with the EOS was verified to match PVT laboratory data obtained under flash and differential liberation processes. It was verified that the interaction coefficient, sigma CH4 - C+ is the relevant parameter for saturation pressure matching. Analysis of regressed parameters indicate, in all four applications, that relevant parameters in the non-linear regression fitting are Omega and Omega of the CH4, fraction.

Introduction

Numerical simulation of gas-condensate and volatile oil reservoirs require the use of compositional simulators due to the changes in composition experienced by the reservoir fluids along the productive life of the reservoir. Phase behavior productive life of the reservoir. Phase behavior modeling of compositional fluids, in modern compositional simulators, is performed by using equations of state, EOS, generally cubic in form.

A number of cubic EOS published in the literature have found wide acceptance in the petroleum industry.

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