Anomalous Foam-Fractional-Flow Solutions at High-Injection Foam Quality

A thorough understanding of foam fundamentals is crucial to the optimal design of foams for improved oil recovery (IOR) or enhanced oil recovery (EOR). This study, for the first time, presents anomalous foam-fractional-flow solutions that deviate significantly from the conventional solutions at high-injection foam qualities by comparing method-of-characteristics and mechanistic bubble-population-balance simulations. The results from modeling and simulations derived from core-flood experiments revealed the following: There are three regions-Region A with relatively wet (or high f(w)) injection conditions in which the solutions are consistent with the conventional fractional-flow theory; Region C with very dry (or low f(w)) injection conditions in which the solutions deviate significantly; and Region B in between, which has a negative df(w)/dS(w) slope showing physically unstable solutions. For dry-injection conditions in Region C, the solutions require a constant state (IJ) between initial (I) and injection (J) conditions, forcing a shock from I to IJ by intersecting fractional-flow curves, followed by spreading waves or another shock to reach from IJ to J. The location of IJ in f(w) vs. S-w domain moves to the left (or toward lower SW) as the total injection velocity increases for both weak and strong foams until it reaches limiting water saturation. Even though foams at high-injection quality are popular for mobility control associating a minimum amount of surfactant solutions, foam behaviors at dry conditions have not been thoroughly investigated and understood. The outcome of this study is believed to be helpful to the successful planning of foam IOR/EOR field applications.