First-contact-miscible and multicontact-miscible gas injection within a channeling heterogeneity system

Experimentally measured recoveries, gas cuts, and residual saturations, as well as visual observations, were used to quantify the effects of a channeling heterogeneity system on the efficiency and gas/oil nonequilibrium of first-contact-miscible (FCM) and multicontact-miscible (MCM) displacements. These experiments are the first of their type, because 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 allMCMexperiments were not in compositional equilibrium. The effect of channeling heterogeneity was to reduce mass transfer between the oil and MCM gas phases throughout the porous medium as a whole, thereby driving the system to be more submiscible 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 FCM and MCM displacement patterns considerably. In addition, the results suggested that the performance of MCM processes decrease significantly as the injection rate increases. This was probably due to an interplay between capillary and viscous forces in the heterogeneous model, causing the gas at the highest rate to flow faster into the high permeability stripe, therefore resulting in a larger transition zone, shorter miscibility region, greater 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 modeling MCM displacements.