In this work, a series of solvent and water injection schemes were conducted on horizontal five-spot glass micromodels which were initially saturated with the heavy oil. Sandstone and limestone rock-look-alike and network patterns, with different pores structures, were etched on glass surfaces. In addition, a validated numerical model based on laboratory data was developed to carry out some sensitivity analysis of different parameters which were difficult to perform on experimental setup. The results confirmed that the ultimate oil recovery of WAS scheme is higher in comparison with the SWAS, and the efficiency of solvent-soak goes further. The WAS scheme resulted in more oil recovery in comparison with the continuous solvent injection at the same value of solvent consumption. Good agreements observed between simulation results and experimental data. The simulation results showed that by increasing the solvent slug size, oil recovery increases before breakthrough, but the trend declines after this time. Increasing water injection rate in WAS and SWAS schemes improved the displacement efficiency. Besides, all above, some pore-scale phenomenon such as viscous fingering, diffusion of solvents into heavy oil, localized entrapment of oil and solvent due to heterogeneity and/or water blockage, and asphaltene precipitation are also illustrated using these pore-level visualization experiments.
The large viscosity contrast between injected miscible solvent and reservoir fluids leads to unstable displacement. The simplest method for controlling this poor mobility ratio is to inject the solvent alternately by water. The Water Alternating Gas (WAG) process, proposed in 1985 by Caudle and Dyes, has remained as the most widely practiced profile to control displacements stably in the oil fields [1]. The WAG process was amid at improving gas flood conformance by simultaneous employed of the natural counteracting tendencies of the gas to rise and the water to descend. The combinations of higher microscopic displacement efficiency of gas with better volumetric sweep efficiency of water help significantly to increase the incremental oil recovery over a water flooding. The process of WAG can be classified in different forms by the methods of fluid injection. The most common categorization is the difference between miscible and immiscible injection. Significant research efforts for optimizing and increasing recovery from WAG process have been provided with better understanding of the injectivity limitations and WAG ratio optimizations [1]. Other criteria such as gas thickeners with gas soluble chemicals, and injectant slug modifications have been proposed [2]. The successful application of miscible and immiscible WAG process in various field tests indicates that high recovery factor and economical solvent- oil ratios are achievable [1,2]. However, there are still several technical challenges to be solved in this process. The pore scale events of heavy oil recovery in the Water Alternating Solvent (WAS), Simultaneously Water Alternating Solvent (SWAS) and Solvent-soak processes were not well understood to the extent of incorporating pore level physics of the process into mathematical models.
