Fundamentals of Fluid Flow in Porous Media
Fluid Properties in Miscible Displacement: Factors Affecting Displacement Efficiency
Displacement efficiency at microscopic (pore level) and macroscopic level in a miscible displacement process are less than 100%. The magnitudes of efficiencies depend on a number of factors, including whether a displacement is secondary or tertiary recovery process.
Microscopic Displacement Efficiency
In a miscible displacement conducted as a secondary recovery process (assume there is not mobile water in the system), the IFT between displaced (oil) and displacing (solvent) phases is zero. According to the Capillary number (Nc) definition, Nc become infinity as IFT goes to zero:
The residual saturation in the portion of the rock contacted by the displacing phase should be essentially zero as Nc → ∞.
Experimental studies of first contact miscibility process show that the residual saturation of the displaced phase is very small when the solvent continuously is injected. However, when the solvent is injected as a small primary slug followed by a secondary slug, recovery can be poorer as a result of dispersion and mixing of different slug materials