Evelyne Neau

A consistent method for phase equilibrium calculation using the Sanchez–Lacombe lattice–fluid equation-of-state

Abstract The Sanchez–Lacombe equation-of-state is known to describe thermodynamic properties of molecular fluids of arbitrary size, mainly polymer–solvent phase behaviour. On the basis of the Helmholtz energy obtained from the partition function of mixtures, chemical potentials are usually derived in order to compute phase equilibrium conditions at various temperatures and pressures. In this work, it is shown that, whatever the mixing rules considered, the chemical potentials derived in this way are thermodynamically inconsistent. The fugacity coefficients derived from the Sanchez–Lacombe equation-of-state are proposed for calculating consistent phase equilibrium conditions.

Modelling solubility of solids in supercritical fluids using fusion properties

Abstract The modelling of solid solubilities in supercritical fluids is usually performed by means of thermodynamic models based on cubic equations of state together with the use of correlations for estimating the solid properties. However, it was shown in the literature, that the error in sublimation pressure, which is very low for high molecular weight compounds, is in many cases responsible for large deviations between experimental and calculated solubilities. In this work, the sublimation pressure of solids is estimated by using experimental fusion data and liquid–vapour equilibrium properties obtained from an equation of state (EOS). The results provided by this method are compared with those obtained using sublimation pressures from literature. It is shown that this method allows satisfactory solubility predictions when using a reliable EOS.

Thermodynamic modeling for petroleum fluids I. Equation of state and group contribution for the estimation of thermodynamic parameters of heavy hydrocarbons

A group contribution method is proposed for estimating the critical properties and acentric factors of paraffins, naphtenes and aromatics with emphasis on extrapolating to very heavy compounds. Group contributions for sulfurized compounds were added to improve further applications in petroleum engineering or in any other domain. From the experimental normal boiling point, critical temperatures were correlated with a 0.6% average deviation on a set of 268 data and critical pressures with a 2.6% deviation on a 222 data set. The normal boiling points can be estimated without any experimental values. With this method, it was possible to correlate the normal boiling points of 641 hydrocarbons and sulfurized compounds with a deviation of less than 0.9%. From these estimated values, a 1% deviation was obtained at the critical temperatures and 2.8% at the critical pressures. The acentric factors of 160 compounds were correlated with a 6.5% deviation. With the proposed method, experimental vapor pressures were predicted using the Peng-Robinson equation of state for 125 compounds with a deviation of less than 5%. The results are compared with those obtained using other methods.

Estimation of model parameters. Comparison of methods based on the maximum likelihood principle

Abstract Neau, E. and Peneloux, A., 1981. Estimation of model parameters. Comparison of methods based on the maximum likelihood principle. Fluid Phase Equilibria, 6: 1–19. Two methods based on the maximum likelihood principle are investigated for the estimation of model parameters from experimental data: the estimated deviation method of Jacq et al. (1979) and Anderson et al. (1978) and the observed deviation method of Peneloux et al. (1975, 1976), Sutton and MacGregor (1977) and Patino-Leal (1979). It is shown that these two methods, which differ in the size of matrices used and in the way of weighting the data, lead to the same values for the model parameters. It is also shown that results do not depend on the fitted functions when an appropriate weighting method is used. The interest of the observed deviation method is discussed. Theoretical results are illustrated in the reduction of binary vapour—liquid equilibrium data.

A new algorithm for enhanced oil recovery calculations

In order to test some algorithms currently available for enhanced oil recovery processes, the evolution of the thermodynamic Minimum Miscibility Pressure (MMP) with respect to the enrichment level of the injection gas by a solvent has been studied. Limitations of classical algorithms are evidenced and an alternative algorithm is proposed.

Thermodynamic modeling for petroleum fluids II. Prediction of PVT properties of oils and gases by fitting one or two parameters to the saturation pressures of reservoir fluids

This paper is devoted to the description of a method for modelling heavy cuts, using either a T.B.ce:simple-para. distillation or an advanced chromatography analysis method. Two sorts of reservoir fluids are defined depending on the advancement of the geochemical catagenetic reactions occurring during the history of the petroleum deposit. Given the existence of differences due to the geochemical history of fluids, two different thermodynamic characterizations may be computed from any given analytical information. One is generally more suitable for use with condensate gases and the other is more appropriate for calculating the physical properties of crude oils. The method presented here involves tuning one or two parameters to one of several saturation pressures of the reservoir fluid. This approach was tested on a data base including more than 50 reservoir fluids. In most cases, the PVT properties predicted using the above method were highly satisfactory.

Thermodynamic modeling for petroleum fluid III. Reservoir fluid saturation pressures. A complete PVT property estimation. Application to swelling test

Abstract This paper is the third one in a series in which a new strategy for modeling heavy petroleum cuts is proposed, with which the PVT properties of gas condensate and crude oils can be completely predicted using a classical one-fluid model with a cubic equation of state. In the second paper in this series, a new method of characterizing petroleum cuts was described. In was concluded that it was necessary to have at least one experimental saturation pressure in order to be able to calculate the PVT properties of a reservoir fluid with a good degree of accuracy. The third paper focuses on the development of a method which can be used to estimate the upper saturation pressure of reservoir fluids at about 100°C. The parameters used in the model were based on correlations involving more than 70 experimental saturation pressures. The method described in this paper, along with the characterization procedure described in the previous paper, makes it possible to completely calculate the PVT properties of a given reservoir fluid. Comparisons are made with other calculation methods described in the literature, and results obtained during gas injection experiments (swelling tests) are discussed.

Vapour—liquid equilibrium of the systems 1-propanol—2,2,4-trimethylpentane and 2-propanol-n-hexane

Abstract The vapour—liquid equilibrium data were measured for the binary systems 2-propanol— n -hexane at 328.21 K and 1-propanol—2,2,4-trimethylpentane at 328.37 K and 348.52 K by using the recirculation still proposed by Berro et al. (1975). The excess volumes for these systems were measured with an Anton Paar densimeter. The reduction of VLE data and analysis of experimental errors were performed. The NRTL temperature-dependence parameters were estimated. The measured VLE data and the activity coefficients were compared with the values predicted by the chemical-reticular group-contribution method (CRG) (Neau and Peneloux, 1979). For both systems satisfactory agreement was found. This proves that the CRG model can be used to predict the vapour—liquid equilibria of alcohol—alkane systems containing branched components.

Equation of state associated with activity coefficient models to predict low and high pressure vapor–liquid equilibria

Abstract A simple and thermodynamically consistent method is presented to establish an equation of state for mixtures by using activity coefficient model parameters. All current solution models such as NRTL, van Laar, UNIFAC, or any other thermodynamic model can be used. The main feature of the method presented is that only a single scaling factor value determined at a given reference temperature is required to predict the vapor–liquid equilibria in a wide range of temperature and pressure. The performance of the method is tested on the prediction of the vapor–liquid equilibria at low, moderate, and high pressures for six binary systems (methanol−benzene, acetone−water, methanol−acetone, methanol−water, ethanol−water, and 2-propanol−water) and a ternary system (acetone−water−methanol). For comparison, vapor–liquid equilibrium calculations were carried out with the Wong and Sandler method by using the PRSV equation of state associated with the van Laar and scaling factors. On the whole, it is found that at high pressures both methods give similar predictions but at low pressures the proposed method gives sometimes better results than that of Wong and Sandler method.

Modelling of the phase behaviour of mixtures in the critical region using the augmented Peng-Robinson equation of state

Abstract The Peng-Robinson equation extended to the PVT property representation in the critical point neighbourhood (PRA equation) was used to calculate binary pressure-composition and pressure-density diagrams. The modified excess function at constant packing fraction model was used to take into consideration binary interactions. In the case of binary systems exhibiting the mixture critical point, calculation results were satisfactory and substantially improved with respect to those obtained using the volume corrected Peng-Robinson (PRC) equation.