Simulation and measurements of volumetric and phase behavior of carbon dioxide + higher alkanes at high pressure: CO2 + n-decane at temperatures (313–410) K and pressures up to 76 MPa

Abstract

Injection of CO2 in hydrocarbon rock formation is one of the proven technologies for both enhanced oil recovery and carbon sequestration. Accurate knowledge of thermodynamic properties of CO2 and reservoir fluid mixtures are required for successful design and operation. In this work, new ρTp and bubble pressure pb measurements are reported for the binary system of carbon dioxide (1)+n-decane (2). Compressed liquid density was determined from the complex resonance frequency of a vibrating U-tube driven by a lock-in amplifier and bubble points were visually detected and also calculated from the discontinuity of a p-V plot of a constant composition isothermal expansion process (CCE). The measurements were made along three isotherms at temperatures T=(313, 363, and 410) K at pressures up to 76MPa for three concentrations of carbon dioxide mole fraction x1=(0.207, 0.471, and 0.730). The experimental results are compared with previous experimental data in literature, and with predictions from four types of equations of state (EOS), commonly used in petroleum and chemical industry: (1) cubic, Peng-Robinson (PR); (2) virial, Benedict−Webb−Rubin−Starling (BWRS); multi-parameters, Groupe European de Recherche Gaziere (GERG-2008); and (4) Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). Analysis of all experimental data, in previous literature and this work, show a systematic increase in deviations from both BWRS and PC-SAFT from 1% to about 10% with increasing carbon dioxide mole fraction which is a clear evidence of the need for adjusting the equation’s parameters, especially at pressures close to bubble points. Best prediction for density was obtained with GERG-2008 EOS, with deviations of about 1%, for all CO2 mole fractions from (0.05 to 0.87), and best prediction for phase behavior was obtained by PR EOS. Earlier experimental data are only limited to 40MPa, while this work extends the measurements to a higher range, of 76MPa and 410K, commonly encountered in gas reservoirs and supercritical CO2 injection processes, and not studied before.