Mechanisms of Miscibility Development in Hydrocarbon Gasdrives: New Interpretation

Abstract

Summary This study concerns the mechanism of miscibility development in multiple-contact-miscible (MCM) gasdrives. Many low-pressure, rich-gas floods, traditionally assumed condensing processes, are shown to be vaporizing or (upper) liquid-extraction drives. It is shown that the solvent phase behavior at reservoir conditions determines the mechanism of miscibility development and that the rich-gas drives in low-temperature reservoirs are mostly condensing processes, while the liquid-extraction mechanism prevails in high-temperature reservoirs. The equation-of-state (EOS) simulations support this new interpretation of rich-gas-drive mechanism. Direct experimental evidence is also provided. The misuse of pseudoternary diagrams and failure to recognize their limitation when applied to multicomponent systems are shown often to lead to a false indication of a condensing processing. This adversely affects interpretation of experimental data (such as interpretation of miscibility in slim-tube displacements), and thus miscible solvent design.