TUNING OF PENG-ROBINSON EQUATION OF STATE FOR SIMULATION OF COMPOSITIONAL CHANGE IN FLUE-GAS INJECTION PROCESSES

The phase behaviour of reservoir hydrocarbon fluids in gas injection p rocesses involve continual mass transfer and composition changes. Comp ositional simulators can predict the phase behaviour of such complex p rocesses, provided the equations of state are properly tuned. The tuni ng method must reflect the great composition changes caused by the mas s transfer. Therefore, the tuning criteria must be based on matching t he predicted compositions with real measured values for the processes, rather than just the saturation pressure and volumetric values. In th is work, the results of extensive experiments on multiple contact gas injection processes are used for tuning the Peng-Robinson equation of state (PR-EOS). The tested fluids were well-defined hydrocarbon system s representing gas condensate and volatile oils and the injectants wer e nonhydrocarbons, N-2, CO2 and their mixtures, as they exist in typic al flue gases. The measured quantities were the volumes and the compos itions of gas and liquid phases at test pressures and temperatures. Th e tuning involved the critical properties and acentric factor of heavy components, the Omega values of the equation of state, as well as the binary interaction coefficients. Completely different tunings were ne eded for a simple volumetric match or for the more complicated composi tion match. The sensitivity checks performed on the tuning parameters have shown that the critical properties of heavy components greatly af fect the compositions, especially those of the liquid phase. (C) 1997 Elsevier Science B.V.