Foam Flow in Heterogeneous Porous Media: Effect of Cross Flow

Abstract

Summary Previous experimental studies of foam generation and transport were conducted, mainly, in one-dimensional and homogeneous porous media. However, the field situation is primarily heterogeneous and multidimensional. To begin to bridge this gap, we have studied foam formation and propagation in an annularly heterogeneous porous medium. The experimental system was constructed by centering a 0.050 m diam cylindrical Fontainebleau sandstone core inside an 0.089 m acrylic tube and packing clean Ottawa sand in the annular region. The sandstone permeability is roughly 0.1 μm2 while the unconsolidated sand permeability is 6.7 μm2. Experiments with and without cross flow between the two porous media were conducted. To prevent cross flow, the cylindrical face of the sandstone was encased in a heat-shrink Teflon sleeve and the annular region packed with sand as before. Nitrogen is the gas phase and an alpha olefin sulfonate (AOS 1416) in brine is the foamer. The aqueous phase saturation distribution is garnered using X-ray computed tomography (CT). Results from this study are striking. When the heterogeneous layers are in capillary communication and cross flow is allowed, foam fronts move at identical rates in each porous medium as quantified by the CT-scan images. Desaturation by foam is efficient and typically complete in about 1 PV of gas injection. When cross flow is prohibited, foam partially plugs the high permeability sand and diverts flow into the low permeability sandstone. The foam front moves through the low permeability region faster than in the high permeability region.