Fluid Phase Equilibria 317 (2012) 52–58 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria j o ur nal homep age: www.elsevier.com/locate/fluid Prediction of volumetric properties of fluids for oil and gas applications Laura A. Pellegrini a , Stefania Moioli a,∗ , Simone Gamba a , Paola Ceragioli b a Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy b Eni E&P Division, Via Emilia 1, I-20097 San Donato Milanese, Milano, Italy a r t i c l e i n f o Article history: Received 27 October 2011 Received in revised form 13 December 2011 Accepted 18 December 2011 Available online 24 December 2011 Keywords: Volume translation SRK EoS PR EoS Pure compound Mixture a b s t r a c t Cubic equations of state are commonly used by the petroleum industry for predicting the phase behavior and the volumetric properties of hydrocarbon fluids. However, the volumetric estimates are not as accu- rate as vapor–liquid equilibrium ones. The present work aims at improving the prediction of density by the use of a proper volume translation correlation. The proposed method, developed from experimental data for alkanes up to twenty-four carbon atoms and for aromatic compounds up to nonylbenzene, shows its reliability for a wide range of temperatures, and for saturated and monophasic liquid and for single components and mixtures as well. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Cubic equations of state, in particular the Soave–Redlich–Kwong (SRK) EoS [1] and the Peng–Robinson (PR) EoS [2], have a good accuracy in representing vapor–liquid equilibrium (VLE) of fluid mixtures when dealing with hydrocarbons and related compounds. In this case, binary interaction parameters (k ij ) can be successfully predicted [3–5]. Other methods based on non-classic mixing rules [6–10] could be successfully used but in some cases, for instance in reservoir conditions, they may be too demanding in terms of computational time. This is the reason why SRK and PR EoSs are widely used in commercial softwares to predict phase behavior and properties of hydrocarbon fluids. However, these equations do not provide an accurate enough estimation of volumetric properties (especially concerning with the liquid phase). Since a reliable prediction of volumetric properties is crucial in many applications – such as, e.g., reservoir charac- terization and design of pipelines and product facilities – several volume translation-based methods (that represent improvements over the original correlation proposed by Péneloux et al. [11]) aim- ing at enhancing the cubic EoS molar volume calculation, have been proposed. These volume shift-based methods have the advantage to retain the “computational simplicity” of a cubic EoS coupled ∗ Corresponding author. Tel.: +39 02 2399 3237; fax: +39 02 7063 8173. E-mail addresses: laura.pellegrini@polimi.it (L.A. Pellegrini), stefania.moioli@mail.polimi.it (S. Moioli), simone.gamba@mail.polimi.it (S. Gamba), Paola.Ceragioli@eni.com (P. Ceragioli). with the consistency of VLE calculation ensured by Péneloux-like translations. Péneloux et al. [11] proposed a very simple correction c for SRK calculated volumes: c = v SRK - v cor (1) where c is the volumetric shift, v SRK is the saturated liquid molar volume calculated by the original EoS and v cor is the correct (exper- imental) saturated liquid molar volume at T R = 0.7. The predictive original correlation, proposed by Péneloux et al. [11] for SRK and applicable to pure hydrocarbons up to n-decane, is: c = 0.40768 ·  RT C P C  · (0.29441 - Z Ra ) (2) where T C and P C are the critical properties of the pure compound and Z Ra is the Rackett compressibility factor. Improved volume translation correlations found in literature (i.e., correlations for c prediction) have been developed on the basis of saturated liquid density data alone or, more seldom, exclu- sively for compounds far from saturation [12]. They can or cannot be temperature-dependent and they use as independent variable either the molecular weight or the normal boiling point of the com- ponent to be characterized [12–16]. For the sake of completeness, it deserves to be mentioned that literature also reports c correlations for both SRK and PR EoSs whose parameters are based on critical compressibility factors (i.e., critical volumes) [17–20] and most of them, when dealing with the sub- critical region, have been developed on the basis of saturated liquid density data alone. In this work, NBP-based parameters have been 0378-3812/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2011.12.022