Study On The Density Measurement And Model Of The CO₂+ Alkanes Systems During CO₂-EOR

CO2-EOR is the win-win choice for it not only enhance oil recovery, but also can storage CO2 to reduce the greenhouse gas in atmosphere. Density change of the CO2+ oil mixtures will influence the movement of CO2 under the oil reservoir. Hence, the density measurement and model of the CO2+ oil systems is crucial for the CO2-EOR. In the paper, some measurements have been done on the density characters of the CO2+ alkanes mixtures, density change of the CO2+alkanes varying with the temperature, pressure, CO2 concentration and the carbon number, also the excess volume and the SAFT model of the CO2 +alkanes mixtures was investigated. The study provides the useful data regarding the reservoir simulation, the selection of the storage site and the movement of CO2 in the CO2-EOR.The magnetic suspension balance (MSB) experimental set up was designed for the density measurement of the CO2+alkanes systems over a wide temperature, pressure and CO2 concentration range. Decane, tetradecane and the decane+tetradecane binary mixtures are used as simulated oil instead the petroleum. The systematic density data of the simulated oil and the CO2+ simulated oil mixtures are established at various temperatures, pressures and CO2 concentrations.The density change of the CO2+ alkanes systems versus temperature, pressure, CO2 concentration and carbon number were investigated based on the measurement. It's found that the density of CO2+ alkanes mixtures showed decrease with the increasing CO2 concentration at high temperature low pressure and high CO2 concentration. It's not benefit for the safety of the CO2 storage. The paper also illustrated the relationship between densities and carbon number, densities of the alkane+alkane and the CO2+ alkanes mixture could be expressed as the one-component alkane and CO2+ alkane system with the same carbon number.High precision density models of the CO2+ alkane system are meaningful for the reservoir simulation and the movement of CO2. In this work, the binary interaction parameter of BWRS equation of state were improved as functions of CO2 concentration, which improved the accuracy markedly. PC-SAFT and tPC-PSAFT models were improved to predict the densities of the CO2+ alkanes systems. Correlations were established for the parameters of the alkanes and the binary interaction parameter as functions of carbon number. The precisions were improved by two improved SAFT compared with the improved BWRS and cubic equations of state, especially near critical conditions. The improved tPC-PSAFT is more suitable for the high CO2 concentration and high temperature high pressure because the consideration of the CO2 polarity. Two improved SAFT could expand from the binary to multi component systems sucessfuly, also can be used to predict densities at the temperatures and pressures out of modelling, which showed strong extension and can be used for general prupose.The excess molar volumes of the CO2+ alkanes were studied at different temperatures, pressures and CO2 concentrations. It found that the negative values of the excess molar volumes were resulted from the filling effects and the dispersion interaction between CO2 and alkanes molecules. The greater the alkane molecule, the stronger the filling effect, which result in more negative of the excess molar volumes. The parameters of the Rdelich-Kister were improved and give a good prediction for the excess molar volumes of the CO2+ alkanes.