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Cubic Equations of State (EoSs) typicallyprovide unreliable predictionsfor phase density and derivative properties at the high-temperature,high-pressure (HTHP) conditions associated with ultradeep petroleumreservoirs (that is, temperatures to 533 K and pressures to 241 MPa).The perturbed-chain statistical associating fluid theory (PC-SAFT)EoS returns improved predictions for density but still can overpredictthe experimental value by up to 5% at HTHP conditions. Not surprisingly,when a modified set of the pure-component PC-SAFT parameters m, σ, and ε/kare fit to HTHPexperimental density data, density predictions throughout the HTHPrange agree with reference data to better than ±1%. However,the lack of such HTHP density data for many hydrocarbons presentsa hurdle to the more widespread use of this PC-SAFT method. This studypresents a group-contribution (G-C) method for calculating PC-SAFTparameters that are designed to yield accurate HTHP density predictions.First- and second-order group contributions are considered. We haveextended the group contribution model of Tihic and co-workers, developedfor polymers, to accurately determine PC-SAFT parameters for alkanes,aromatics, and cycloalkanes at temperatures to 533 K and pressuresto 276 MPa. The parameter values are a function of contributions fromthe various functional groups present and the nature of the variouscarbon atoms (aliphatic, aromatic, and naphthenic) comprising themolecule. Furthermore, when using second-order group contributions,it is possible to distinguish the differences in density among isomers.Density values are usually calculated to within ±1–2%.Isothermal compressibility values are calculated to within ±10%,isobaric heat capacity to within ±5%, and speed of sound to within±4%. [ABSTRACT FROM AUTHOR]

Abstract: This research focuses on providing the petroleum reservoir engineering community with robust models of hydrocarbon density and viscosity at the extreme temperature and pressure conditions (up to 533K and 276MPa, respectively) characteristic of ultra-deep reservoirs, such as those associated with the deepwater wells in the Gulf of Mexico. Our strategy is to base the volume-translated (VT) Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK) cubic equations of state (EoSs) and perturbed-chain, statistical associating fluid theory (PC-SAFT) on an extensive data base of high temperature (278–533K), high pressure (6.9–276MPa) density rather than fitting the models to low pressure saturated liquid density data. This high-temperature, high-pressure (HTHP) data base consists of literature data for hydrocarbons ranging from methane to C40. The three new models developed in this work, HTHP VT-PR EoS, HTHP VT-SRK EoS, and hybrid PC-SAFT, yield mean absolute percent deviation values (MAPD) for HTHP hydrocarbon density of ∼2.0%, ∼1.5%, and <1.0%, respectively. An effort was also made to provide accurate hydrocarbon viscosity models based on literature data. Viscosity values are estimated with the frictional theory (f-theory) and free volume (FV) theory of viscosity. The best results were obtained when the PC-SAFT equation was used to obtain both the attractive and repulsive pressure inputs to f-theory, and the density input to FV theory. Both viscosity models provide accurate results at pressures to 100MPa but experimental and model results can deviate by more than 25% at pressures above 200MPa. [Copyright &y& Elsevier]

Abstract: At pressures below ∼55MPa, the perturbed chain – statistically associated fluid theory (PC-SAFT) gives reliable density predictions within ±2% for n-alkanes and other hydrocarbons. However, PC-SAFT tends to over-predict density values by as much as 5% at higher pressures, particularly for normal and branched alkanes. For many compounds, literature values for the three pure-component PC-SAFT parameters m, σ, and ɛ/k B are typically obtained by fitting the equation to sub-critical PρT data or occasionally both sub-critical and supercritical density data. A new set of pure-component PC-SAFT parameters for density prediction at extreme conditions is reported here by fitting the PC-SAFT equation to single-component density data collected at temperatures from ambient to 533K and pressures from ∼6.9 to 276MPa, rather than sub-critical density data since these high temperature, high pressure (HTHP) conditions are similar to conditions typically associated with petroleum recovery from ultra-deep formations. Density predictions made using the new, HTHP PC-SAFT pure-component parameters at HTHP conditions are clearly superior to those obtained using the original PC-SAFT parameters. Although a correction term can be applied to the ɛ/k B parameter to make HTHP PC-SAFT pure-component density predictions at pressures below 6.9MPa only slightly inferior to predictions with the original PC-SAFT parameters, vapor–liquid equilibrium predictions with the original PC-SAFT parameters are clearly superior to predictions made with the HTHP parameters. Correlations are developed to accurately predict the HTHP PC-SAFT parameters for normal and branched alkanes for which there are either incomplete or nonexistent experimental density data sets. [Copyright &y& Elsevier]

Binary mixture density data are reported for propane (C 3 ) with n -decane (C 10 ) and with n -eicosane (C 20 ) at T = (320 to 525) K and pressures to 265 MPa. The (C 3 + C 10 ) mixture density data are in good agreement with available literature data to 70 MPa, which is the maximum reported literature pressure. There are no available binary mixture density data to compare to the (C 3 + C 20 ) mixture density data reported in the present study. The mixture density data are correlated with the Tait equation to facilitate interpolation of the data at different experimental conditions. Equations of state that are suitable for reservoir simulations are used to model the reported data. These models include the Peng–Robinson equation of state (PREoS), a volume-translated PREoS fit to high temperature, high pressure (HTHP) pure component density data, the PC-SAFT EoS, and modifications of the PC-SAFT EoS developed for better representation of HTHP data. The models give superior density predictions for (C 3 + C 10 ) mixtures compared to (C 3 + C 20 ) mixtures. [ABSTRACT FROM AUTHOR]

The cisand transconformationof a branched cyclic hydrocarbon affects the packing and, hence, thedensity, exhibited by that compound. Reported here are density datafor branched cyclohexane (C6) compounds including methylcyclohexane,ethylcyclohexane (ethylcC6), cis-1,2-dimethylcyclohexane(cis-1,2), cis-1,4-dimethylcyclohexane(cis-1,4), and trans-1,4-dimethylcyclohexane(trans-1,4) determined at temperatures up to 525K and pressures up to 275 MPa. Of the four branched C6 isomers, cis-1,2 exhibits the largest densities and the smallestdensities are exhibited by trans-1,4. The densitiesare modeled with the Peng–Robinson (PR) equation of state (EoS),the high-temperature, high-pressure, volume-translated (HTHP VT) PREoS,and the perturbed chain, statistical associating fluid theory (PC-SAFT)EoS. Model calculations highlight the capability of these equationsto account for the different densities observed for the four isomersinvestigated in this study. The HTHP VT-PREoS provides modest improvementsover the PREoS, but neither cubic EoS is capable of accounting forthe effect of isomer structural differences on the observed densities.The PC-SAFT EoS, with pure component parameters from the literatureor from a group contribution method, provides improved density predictionsrelative to those obtained with the PREoS or HTHP VT-PREoS. However,the PC-SAFT EoS, with either set of parameters, also cannot fullyaccount for the effect of the C6 isomer structure on the resultantdensity. [ABSTRACT FROM AUTHOR]

Abstract: The performance of the SRK and PR cubic equations of state (EoS) for predicting molar volumes at the extremely high temperature, high pressure (HTHP) conditions associated with ultra-deep petroleum formations, are improved with a temperature-dependent volume-translation (VT) term. Rather than correlating the volume-correction to saturated liquid densities, as is done in most prior volume translation methods, the volume-translation term in the HTHP VT-SRK EoS and HTHP VT-PR EoS is correlated to pure component, single-phase density literature data at pressures between 7 and 276MPa and temperatures between 278 and 533K. VT parameters are determined for 17 compounds, including short- and long-chain alkanes ranging from CH4 to n-C40H82, several cycloalkanes, and several aromatics. Our recent HTHP density data for several hydrocarbons have been included in this HTHP density data base to enhance the accuracy of these models. The volume correction parameters are correlated to the inverse of the product of the molecular weight and acentric factor, (Мω)−1, allowing these models to be used for compounds not included in the data base. The mean absolute percentage deviation (MAPD) values of (1–2%) and (1–4%) obtained with the HTHP VT-SRK EoS and HTHP VT-PR, respectively, are substantially better than those obtained with other models. The proposed models are also successfully extended to mixtures. The new HTHP VT-EoSs do not exhibit any thermodynamic inconsistencies as illustrated by the determination of density, isothermal compressibility, and speed of sound calculations over a very broad range of temperature and pressure. [Copyright &y& Elsevier]

Abstract: Experimental densities are reported for n-hexadecane, n-octadecane, and n-eicosane at pressures to ∼265MPa and temperatures of 323.15, 423.15, and 523.15K. The reported densities are in good agreement with the available literature data that cover limited pressure and temperature ranges. The Peng–Robinson equation of state (PR EOS), a new high-temperature high-pressure volume-translated Soave–Redlich–Kwong equation of state (HTHP-VT SRK EOS), and the perturbed-chain statistical associating fluid theory (PC-SAFT) are used to predict the reported densities. Both the HTHP-VT SRK and PC-SAFT equations exhibit mean absolute percent deviation (MAPD) values of 2.4–1.3% for the densities of all three hydrocarbons while the MAPD values for the PR EOS are all near 16%. [Copyright &y& Elsevier]