Effect of dispersion on local displacement efficiency for multicomponent enriched-gas floods above the MME

Research on four-component one-dimensional displacements has shown that enriching the gas above the minimum enrichment for miscibility (MME) can substantially increase oil recovery for certain systems. Research has further shown that the oil recovery increase can be very sensitive to the level of dispersion at the enrichment chosen. The main focus of this paper is to extend the research on four-component systems to displacements of multicomponent oils and gases where the recovery is affected by dispersion and enrichment. We consider here a twelve-component oil displaced by solvents enriched above the MME. For this case, the increase in recovery (displacement efficiency) above the MME can be as large as 15% OOIP depending on the level of mixing. The methodology outlined can be used as a screening tool to identify if a significant benefit may exist and further 2-D and 3-D studies are warranted. A secondary focus of the paper is to examine in detail how dispersion affects recoveries and displacement mechanisms for the four and twelve-component systems. We show that for the case of the four-component model the displacement mechanism changes from a combined condensing/vaporizing displacement (CV) to a strictly condensing one as enrichment increases above the MME. We also show how to quantify the percentage of the CV displacement that is vaporizing or condensing by calculating the compositional distances between key tie lines identified from “dispersion-free” theory.