Research on the precise calculation method of physical parameters for CO2

The pressure and temperature affect in the physical property parameters of CO2 greatly, especially near to the surrounding of critical zone. The parameters of density, heat capacity at constant pressure, heat capacity under constant volume, et al. were calculated at different state conditions for CO2 using the Span-Wagner equation of state (S-W EOS). The results were compared with the experimental data reported in the reference, and the conclusion was that the error range is no more than 2% which means that the precision of calculation results is higher. At the same, the density of CO2 was calculated using the P-R EOS which has higher precision, and the calculation error was given; then the result was compared with that of S-W EOS, and the calculation error of P-R EOS was higher than that of the S-W EOS. The maximum value of the former was up to 11% or more, which can not meet the engineering calculation demand, however, the calculation error of S-W EOS was within 0.5%. S-W EOS will provide the basis for accurate prediction of borehole temperature and pressure in CO2 gas well production, CO2 enhanced oil recovery and other projects.