Abstract

Some surfactants we tested were found to be more capable of selectively reducing gas mobility by a greater fraction in high-permeability sands. It is expected that foam can mitigate the problem of an early gas breakthrough in EOR processes. Laboratory experiments were conducted to examine the effect of foam on two different systems of porous media with various fluid saturations. The first system was a fired Berea sandstone core with relatively homogeneous permeability. To simulate reservoir heterogeneity, the second system was a composite core of coaxial permeability (high and low) layers in capillary contact. Experiments were conducted in these systems by injecting CO₂, CO₂/brine, or CO₂/foam into core with different fluid saturations (brine, surfactant solution, and oil). The breakthrough time and incremental fluid recovery were recorded and compared. This study indicates that foam could delay CO₂ breakthrough time and improve oil recovery efficiency in both single and composite cores. The experimental results of the composite core tests also showed a significant improvement in oil recovery from the low permeability region when CO₂/foam was used.