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

Compositional simulation and analytical solutions are presented that model enriched gas drive processes using only four pseudocomponents. A four-component model is used and compared to a more detailed 12-component model to examine the effects of dispersion, gas enrichment and pressure on oil recovery. We show that a simple four-component lumping method can give a model with acceptable average front velocities that exhibits features of both condensing and vaporizing displacements. Furthermore, we show that a four-component model can achieve a nearly exact match to the 12-component model if the four-component enrichment level is adjusted. 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).