Abstract:

A suitable Equation of State (EOS) was developed for multi component, multi phase systems from the Peng-Robinson Equation of State using a newly developed variable parameter ‘a’ approach (VPAA) which treats the attractive term parameter as a variable regressed by two straight lines. This EOS was used to determine the stability limit curves for crude oils from three different oil wells on the application of the Helmholtz free energy criterion for intrinsic stability. This was used along with the T-isotherm for the crude oils and the stability limit was found by locating the point of intersection of the two curves. For Well-1, the vapor phase was unstable while the liquid phase was stable at 47.4 atm. For Well-2, the vapor phase was stable at 209 atm. while the liquid phase was stable at two pressure values of 191atm. and 213 atm. For Well-3 however, the vapor phase was stable at 45.7 atm. while two liquid phases were identified. The lighter one was unstable at the temperature of interest, while the heavier one was stable at 115.9 atm.

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