Liquid density calculations

The results of the reservoir liquid density calculations can be used to calculate oil formation volume factors. 

From the preceding check of n-octane liquid density, we have established that Eq. (1.14) is a reasonable source for calculating ra-octane liquid density. Both Nelson and Maxwell data points could also have as much error, 1 to 3%. The conclusion therefore is that Eq. (1.14) is a reasonable and reliable method for liquid density calculations. You may desire to investigate other known liquid densities having the same known variables, Tc, Pc, and MW. You are encouraged to do so. 

The liquid density calculated from the Soave EoS is 24.2 percent below the DIPPR 801 recommended value of 29.69 kmol/m, while that calculated from the Peng-Robinson EoS is 13.9 percent below the recommended value. 

The Soave equation is widely used for hydrocarbons and related components over broad ranges of temperature and pressure. It is accurate enough for calculating enthalpy and entropy departures, vapor-liquid equilibria, and vapor density in natural gas processing and many petroleum-related operations. The equation is not very accurate in the critical region and for liquid density calculations. 

Table 3. Comparison of saturated liquid densities calculated by SRK EOS, former volume translation models based on SRK EOS, and three liquid density correlations (RSD, NM,...

As is evident, the BWR-11 is not as accurate as most of the empirical correlations (exception Watson (26)) that have been derived specifically for predicting liquid density. Calculations involving the design of storage areas, and especially custody transfer definitely require the more accurate empirical equations. 

The equation shows its best advantages in any situation involving liquid density calculations and in situations near the critical region, but it is usually better than other two parameter models in all regions. 

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