First-contact-miscible, vaporizing- and condensing-gas drive processes in a channeling heterogeneity system

Experimentally measured recoveries, gas cuts and residual saturations as well as the visual observations were used to quantify the effects of channeling heterogeneity system on efficiency and gas/oil nonequilibrium of first- and multi-contact miscible (MCM) displacements. These experiments are the first of their kind as they have enabled a direct insight into the mechanisms of gas/oil flow occurring within such type of heterogeneities, and particularly have provided a firmer understanding of the MCM processes. The key finding in this work is the fact that the produced fluids in all MCM experiments were not in compositional equilibrium. The effect of channeling heterogeneity was to lower mass transfer between oil and MCM gas phases throughout the porous medium as a whole, thereby driving the system to be more sub-miscible and as such reducing the sweep and increasing the bypassing. These results were also reflected in the increase in nonequilibrium between gas and oil phases. This work has proved that the channeling heterogeneities, even with small permeability contrast, can distort first- and multi-contact miscible displacement patterns considerably. Additionally, the results suggested that the performance of MCM processes decrease significantly with the increase in injection rate. This was probably due to an interplay between capillary and viscous forces in the heterogeneous model causing the gas at highest rate to flow faster into the high permeability stripe, and therefore resulting in a larger transition zone, shorter miscibility region, higher nonequilibrium and hence a lesser efficient flood. This study has important implications for the correct interpretation of core data, and for scale-up processes to reservoir scale, particularly for handling gas/oil nonequilibrium when modelling MCM displacements.