Oil recovery by alkaline/surfactant/foam flooding: Effect of drive-foam quality on oil-bank propagation

Alkaline/surfactant/foam (ASF) flooding is a novel enhanced-oil-recovery (EOR) process that increases oil recovery over waterflooding by combining foaming with a decrease in the oil/water interfacial tension (IFT) by two to three orders of magnitude. We conducted an experimental study regarding the formation of an oil bank and its displacement by foam drives with foam qualities within the range of 57 to 97%. The experiments included bulk phase behavior tests using n-hexadecane and a single internal olefin sulfonate surfactant, and a series of computed-tomography (CT) -scanned coreflood experiments using Bentheimer Sandstone cores. The main goal of this study was to investigate the effect of drive-foam quality on oil-bank displacement. The surfactant formulation was found to lower the oil/water IFT by at least two orders of magnitude. Coreflood results, at under-optimum salinity conditions yielding an oil/water IFT on the order of 10-1 mN/m, showed similar ultimate-oil-recovery factors for the range of drive-foam qualities studied. A more distinct frontal oil-bank displacement was observed at lower drive-foam qualities investigated, yielding an increased oil-production rate. The findings in this study suggested that dispersive characteristics at the leading edge of the generated oil bank in this work were strongly related to the surfactant slug size used, the lowest drive-foam quality assessed yielded the highest apparent foam viscosity (and, thus, the most stable oil-bank displacement), and drive-foam strength increased upon touching the oil bank when using drive-foam qualities of 57 and 77%.