Equation of state for hydrocarbons and water

Equation of state for hydrocarbons and water Reservoir fluids consist mainly in multi-component system of hydrocarbons, non-hydrocarbons and formation water. Therefore, the reservoir fluids chemical composition is in many cases complex. Analytical equation of state (EOS) is used to calculate the volumetric and phase behavior of the reservoir fluids. EOS starts from simple ideal gas equation by Émile Clapeyron in 1834, but it had a lot of limitations regarding it’s applicability at real reservoir conditions. As van der Waals (1873) introduced his equation of state, it used to generalize the ideal gas law based on the fact that gases behave as real gases, even it doesn’t have any practical applications nowadays it was considered the basis for revolution in developing and enhancing EOS. In Redlich and Kwong (RK, 1949) equation they included the temperature of the system to the van der Waals attraction term to consider its effects on the intermolecular attractive forces among the atoms which has improved the equation accuracy but it was not the last possible improvements to the VdW equation of state, the Soave-RK (1972) EOS was born as modification on RK EOS with a very good potential as it had overcome the fact that the RK equation was not accurate to express the effect of temperature which in turn improved the application of the equation of state to multicomponent vapor-liquid equilibrium (VLE) calculations. Then, Peng and Robinson (PR, 1976) improved the ability of the equation of state for prediction of densities of liquid and other fluid properties, particularly near the critical zone. Finally, Peneloux et al. (1982) introduced a way to improve the volume predictions for the two parameter SRK EOS by using a volume correction factor, similarly Jhaveri and Youngren (1984) used volume correction factor for the two parameter PR EOS. Furthermore, for water and by using Tait equation (1888) which is considered one of the most famous empirical equations of state for water along with its modified versions by Tammann (1911) and Gibson (1935). Which is used to correlate volume of liquid to pressure and where B and C are Tait equation parameters. The C parameter was found by Gibson and Loeffier (1941) and equal to (0.3150 x Vo) while many attempts aimed to discover B for water and B* for sea water. It was found that the most internally consistent PVT data on water compared to the Tait equation are the values of Amagat (1893) and Ekman (1908).