PVT Consulting and Simulation Software

Calsep is a leading provider of PVT simulation services to the oil and gas industry

Calsep has more than 30 years of experience working with the oil industry on projects related to reservoir fluid phase behavior. That allows us to offer knowledge-based PVT simulation software and studies within EoS modeling of all kinds of fluids including natural gases, gas condensates, near critical fluids, black oils, and heavy oils. Calsep undertakes projects with application for reservoir simulation, flow assurance, and process simulation.

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International experts in EOS modeling

Calsep undertakes fluid modeling studies assessing all stages of production. The studies may cover the effect of injection gas in the reservoir for EOR purposes as well as the risk and mitigation of solid precipitation in wells and pipelines. Calsep can deliver fluid property or composition input files for more than 20 different reservoir, flow and process simulators.

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Develop your own PVT modeling skills

Calsep offers open courses as well as in-house courses to reservoir engineers, process engineers, engineers dealing with flow assurance or multi-phase flow metering, laboratory staff and others needing to apply PVT simulation software in their work.

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PVTsim Nova

A leading PVT simulation software

PVTsim Nova was launched May 2014 as a new generation of the PVTsim software package that has been continuously developed since the first version was released in 1988. Powerful and reliable simulation options wrapped in a user-friendly graphical user interface has made PVTsim the preferred PVT simulation tool of more than 200 companies in oil and gas industry.

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How good are the predictions of sound velocity with an equation of state?


It was a major achievement when Peneloux et al. in 1982 presented the method for volume correcting a cubic equation of state. It enabled liquid densities to be matched using a cubic equation, which was not possible with the equations in their original form. Prior to that time cubic equations had mainly been used to calculate phase amounts and compositions and to some extent gas Z-factors while liquid densities were calculated using external liquid density correlations.  The volume correction made the empirical density correlation redundant.

The volume correction can be treated as a constant or as a function of temperature. PVTsim supports a volume correction, which varies linearly with temperature, which will enable a good match of the isobaric compressibility. The volume correction has only marginal influence on isothermal compressibility and velocity of sound. While the isothermal compressibility can be derived from routine PVT studies, the data material for the sound velocity of reservoir fluids is scarce. The sound velocity is defined as


M = Molecular weight

V = Molar volume

P = Pressure

S = Entropy


Acoustic techniques used in oil exploration are dependent on models providing an accurate sound velocities and sound velocity is a key property in dynamic flow simulations. Calsep regularly receives requests about the accuracy that can be expected with PVTsim for sound velocity. Following those requests Calsep conducted a literature search for sound velocity data for petroleum reservoir fluids. Sound velocity data was found for 4 reservoir fluids, two gas condensates and two oil mixtures. The data material covered temperatures from 0-180 oC and pressures from 1 – 1200 bar. The data was simulated using the volume corrected SRK and PR equations and the PC-SAFT equation and the results documented in a validation report available to PVTsim users upon request: “Validation of PVTsim sound velocity predictions using SRK-Peneloux, PR-Peneloux and PC-SAFT”.

For gas condensates PR-Peneloux was superior to the two other equations while for oil mixtures the better results were seen with the PC-SAFT equation.  In general the sound velocity can be simulated within 10% by choosing the appropriate equation of state. Figures 1 and 2 plots exemplifying the deviations between simulated and experimental data.


Figure 1. Match of sound velocity data for gas condensate mixture with PR-Peneloux EoS. Series are pressures in bar.


Figure 2. Match of sound velocity data for oil mixture with PC-SAFT EoS. Series are pressures in bar.



  1. A. Barreau, K. Gaillard, E. Béhar, J.L. Daridon, B. Lagourette, P. Xans. Volumetric properties, isobaric heat capacity and sound velocity of condensate gas measurements and modelling. Fluid Phase Equilibria, Volume 127, Issues 1–2, 15 January 1997, pp. 155-171.

  2. J.L. Daridon et al. Petroleum characterization from ultrasonic measurement. Journal of Petroleum Science and Engineering 19,1998, pp. 281–293.

  3. Wang, Z., Nur, A. M., & Batzle, M. L. (1990, February 1). Acoustic Velocities in Petroleum Oils. Society of Petroleum Engineers. doi:10.2118/18163-PA.