Prediction of hydrocarbon densities at extreme conditions using volume-translated SRK and PR equations of state fit to high temperature, high pressure PVT data

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.