Abstract
The phase behavior of solvent-oil mixtures as it relates to enhanced oil recovery operations is reviewed. Typical phase envelopes for a model binary hydrocarbon mixture and for mixtures of an oil with a hydrocarbon solvent and with CO2 are presented.
Experimental data were obtained for an enhanced oil recovery study of the South East Nasser reservoir fluid with a NGL/Dry Gas solvent and with CO2. Swelling tests, phase equilibrium measurements and slim tube runs were conducted with both solvents. It is concluded that the minimum miscibility content of NGL in the solvent and the minimum miscibility pressure when using CO2, both occur at conditions where theoretical predictions would suggest that miscibility has in fact not been achieved. Nevertheless, all key indicators would suggest very efficient displacements supported also with high displacement efficiencies.
A combination of visual observations and calculations represented on a pseudo ternary component diagram suggest that the hydrocarbon displacements correspond to a combined condensing-vaporising type mechanism.
The detailed nature of the displacement mechanism in the presence of carbon dioxide is shown to depend on the relative amount of the lighter compared to the heavier components in the parent oil.