PC-SAFT Equation of State Applied to Petroleum Reservoir Fluids

Abstract

Abstract The PC-SAFT equation has been proposed as a potential next generation equation of state in the oil industry. It has already obtained widespread use for simulations on polymer systems, which shows that it has a capability of handling phase equilibria for systems with heavy hydrocarbons. A C7+ characterization procedure for use with the PC-SAFT equation has been developed and used to test how PC-SAFT performs on various types of petroleum reservoir fluids ranging from natural gas mixtures to heavy oils with asphaltenes. Promising results are seen for asphaltene onset pressures and for oil mixtures in general. With the currently published pure component parameters PC-SAFT is inferior to cubic equations of state for simulations on gas and gas condensate mixtures. Introduction For more than 50 years cubic equations of state have been a standard for thermodynamic calculations in the oil industry. The cubic equations of state date back to the van der Waals equation1 from 1873. Several modifications were proposed in the twentieth century. The first cubic equation to obtain widespread use in the oil industry was the Redlich-Kwong equation2 from 1949. Today the most commonly applied cubic equations are the Soave (SRK) modification3 of the Redlich-Kwong equation proposed in 1972 and the Peng-Robinson (PR) equation4 from 1976. Cubic equations are applicable for both phase equilibrium and density calculations, but generally provide too low liquid densities in their original form. This deficiency was for many practically purposes overcome when Peneloux at al.5 in 1982 proposed a volume corrected cubic equation of state providing more accurate liquid densities without influencing phase equilibrium simulation results.