Effect of gas enrichment and dispersion on nearly miscible displacements in condensing/vaporizing drives

Compositional simulation and analytical solutions are presented to show the validity of modeling enriched gas drive processes using only four pseudocomponents. The four-component model is used and compared to a more detailed 12-component model to analyze the effects of dispersion, gas enrichment and pressure on the oil recovery. We show that a simple four-component lumping method gives a model with acceptable average front velocities that exhibits features of both condensing and vaporizing displacements. Furthermore, we show that the four-component model can achieve a nearly exact match to the 12-component model by adjusting the four-component enrichment level. We also compare the dispersion-free analytical four-component solution with a dispersive four-component compositional simulation to demonstrate that dispersion causes some two-phase flow in a displacement that would otherwise be multicontact miscible (MCM). As dispersion increases in both the four and 12-component models, the oil recovery is reduced, especially near the minimum enrichment for miscibility (MME).