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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]

DuPont's perfluoropolyether oil Krytox $$^{\textregistered }$$ GPL 102 is a promising candidate for the high-temperature, high-pressure Deepwater viscosity standard (DVS). The preferred DVS is a thermally stable liquid that exhibits a viscosity of roughly 20 $$\hbox {mPa} \cdot \hbox {s}$$ at 533 K and 241 MPa; a viscosity value representative of light oils found in ultra-deep formations beneath the deep waters of the Gulf of Mexico. A windowed rolling-ball viscometer designed by our team is used to determine the Krytox $$^{\textregistered }$$ GPL 102 viscosity at pressures to 245 MPa and temperatures of 311 K, 372 K, and 533 K. At 533 K and 243 MPa, the Krytox $$^{\textregistered }$$ GPL 102 viscosity is $$(27.2 \pm 1.3)\,\hbox {mPa} \cdot \hbox {s}$$ . The rolling-ball viscometer viscosity results for Krytox $$^{\textregistered }$$ GPL 102 are correlated with an empirical 10-parameter surface fitting function that yields an MAPD of 3.9 %. A Couette rheometer is also used to measure the Krytox $$^{\textregistered }$$ GPL 102 viscosity, yielding a value of $$(26.2 \pm 1)\,\hbox {mPa} \cdot \hbox {s}$$ at 533 K and 241 MPa. The results of this exploratory study suggest that Krytox $$^{\textregistered }\, \hbox {GPL}$$ 102 is a promising candidate for the DVS, primarily because this fluoroether oil is thermally stable and exhibits a viscosity closer to the targeted value of 20 mPa $$\cdot $$ s at 533 K and 241 MPa than any other fluid reported to date. Nonetheless, further studies must be conducted by other researcher groups using various types of viscometers and rheometers on samples of Krytox GPL $$^{\textregistered }$$ 102 from the same lot to further establish the properties of Krytox GPL $$^{\textregistered }$$ 102. [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: 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]