Further discussion of methodology for the specification of solvent blends for miscible enriched-gas drives

When an injected gas comes into contact with a reservoir oil, mass transfer of individual components in both fluids takes place. With injection of a dry gas, miscibility develops by vaporization at the leading edge of the gas front. This process we call a leading-edge, or forward-contact, vaporizing process. We have recently completed a study of the effect of temperature on minimum miscibility pressure (MMP) for a crude oil using CO₂ as the injected gas. The enrichment of the CO₂ with only 6% normal butane lowered the MMP from 290 to 520 psi, depending on the temperature. With CO₂, the process was a leading edge, or forward contact, vaporizing process, whereas adding only 6% normal butane to the injected CO₂ caused the process to be a trailing-edge, or swept-zone, condensing process.