Viscous Fingering, Gravity Segregation, and Reservoir Heterogeneity in Miscible Displacements in Vertical Cross Sections

Abstract

Abstract Combined effects of gravity segregation, viscous fingering and reservoir heterogeneity are examined in particle-tracking simulations of flow in vertical cross sections. Differences in model formulation from previous descriptions are reviewed briefly. The accuracy of the simulation representation of the physical flow mechanisms is tested. For homogeneous cross sections, simulator calculations are presented that illustrate the transition from flow in a single gravity-dominated tongue at low viscous to gravity ratio (Ngr) to flow dominated by viscous fingering at high values of Ngr. Quantitative accuracy of the simulator is tested against the experimental results of Pozzi and Blackwell. Simulation results agree with experimental results over wide ranges of mobility ratio, viscous to gravity ratio, and aspect ratio. Additional simulations also agree well with Stalkup's correlation of breakthrough recovery as a function of mobility ratio and Ngr. The validated simulator is then used to augment Stalkup's correlation with results for additional mobility ratios. In addition, plots are presented of recovery after breakthrough as a function of Ngr for several mobility ratios. The results confirm that in homogeneous porous media, better displacement performance is observed at high viscous to gravity ratio for any mobility ratio. For heterogeneous porous media, however, that conclusion must be qualified. Example simulation results show that for injection of light solvent into a layered reservoir with high permeability low in the reservoir, better displacement efficiency is observed at intermediate values of Ngr than at high or low values. If the high permeability is at the top of the reservoir, high Ngr is still preferred.