This paper presents the predictions and calculations of the phase equilibria of oil, gas and water/brine mixtures where the oil and gas are modeled by a cubic equation of state and where the gas solubility in the aqueous phase is estimated from Henry's law. Henry's law constants for a variety of compounds of interest to the petroleum industry are correlated against pressure and temperature. The scaled-particle theory is used to take into account the presence of salt in the aqueous phase. An extensive match of experimental data is presented, showing the adequacy of the proposed model for Henry's law constant.On donne dans ce travail les pridictions et les calculs d'kquilibre de phase des mClanges pktrole, gaz et eau-saumure, 00 le pktrole et les gaz sont reprksentis par une Cquation d'itat cubique et ou la solubilite des gaz dans la phase aqueuse est estimie a I'aide de la loi d'Henry. Les constantes de Henry sont corrClCes pour une large gamme de composis d'intiret pour I'industrie pktroliere, en fonction de la pression et de la tempkrature. On utilise la thiorie des particules ajusties pour tenir compte de la prisence de sel dans la phase aqueuse. On prksente une vaste comparaison de donnies expkrimentales qui montre la validiti du modkle propost5 pour les constantes de la loi d'Henry. ater exists abundantly in hydrocarbon reservoirs, either where y,, denotes the mole fraction of component i in phase m. K,,, = yIw/y,e 486 THE

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In phase behaviour calculations and compositional simulations with an equation of state, it is advantageous to represent the oil and gas systems by a small number of pseudo-components. This paper presents a scheme for determining these pseudocomponents based on the K-values of all constituents that are present in the reservoir oil and gas systems. The scheme is simple and applicable to both the light and heavy components. Sensitivity studies are carried out to investigate the effect of different pseudo-component representations on the shape of various phase diagrams, and on the compositional simulation results. Introduction Phase behaviour calculations and compositional simulations with an equation of state require the use of pseudocomponents to represent the oil and gas mixtures. Because of the large number of components which form the heavy fractions (e.g. C6 + fractions), it is necessary to group them into pseudo-components. Furthermore, to minimize simulation costs, it is also advantageous to lump the light fractions. This paper presents a procedure for characterizing the heavy fractions of oil and gas and a systematic scheme for lumping the components into pseudo-components based on the K-values at a specified operating condition which is typical of the process under study. Phase diagrams are then generated to investigate the effects of different lumping schemes on the shape of the phase boundaries and quality lines. The construction of these phase diagrams provides a rapid method for examining the sensitivities of the computed phase behaviour to different lumping schemes over a wide range of pressure, temperature and composition. Compositional simulation with different lumping schemes is also carried out to investigate the effect of different pseudo-component representations on the simulation results. Extended Analysis of Heavy Fractions Extended analyses of the heavy fractions (e.g. C6 + fraction) are required for accurate predictions of oil and gas phase behaviour from an equation of state (EOS)(1). True-boiling-point (TBP) analyses yield directly the boiling point, specific gravity and the molecular weight of each carbon-number (CN) group(2) from which molar distribution is found directly. Analyses from gas-chromatograph (GC) measurements, on the other hand, provides only the weight fraction of each CN group. The molar distribution is then obtained by using either the molecular weight of the normal alkane corresponding to each CN group, or the data of Katz and Firoozabadi(3, 4). The results obtained from ac measurements are less accurate than those obtained from TBP experiments. If only a partial extended analysis is available, it can be extended to higher CN group by using the method of Whitson(1), Pedersen et al.(5) or the one described in Appendix A. The critical properties and eccentricities of the CN groups are estimated from their specific gravities and boiling points by using Kesler-Lee correlations(6). If the specific gravity and boiling point of any CN group are not available, they can be estimated from the data of Katz and Firoozabadi(3, 4) or from the correlations reported by Whitson(7). Lumping into Pseudo-Components Because of the large number of components in the heavy fraction, it is necessary to lump them into pseudo-components before an EOS can be used efficiently.

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This paper deals with the development of a general algorithm for phase envelope construction. It extends the pressure-temperature diagram construction method of Michelsen to the generation of phase envelopes on pressure-composition, temperature-composition and composition-composition diagrams.The bubble point and dew point curves are traced in one pass, and an estimate of the critical point is also given. The loci of mixtures having a constant vapor-liquid split (e.g. 25% vapor mole fraction or volume fraction) can also be generated. The algorithm selects i ntern ally the primary variab 1 es and the poi nts on the di agram to enhance the convergence.