Foam Dynamics in Limestone Carbonate Cores

There is an increasing interest in foam applications in heterogeneous carbonate reservoirs to improve gas sweep and mitigate a high gas-oil ratio (GOR) in production wells. However, foam has been studied in sandstones more than in carbonates, and there are few experimental investigations considering matrix transport properties of foam in carbonates. Thus, this study takes a fundamental approach to improve our understanding of foam generation and transport process in the absence and presence of remaining oil in carbonates by co-injection of Alpha Olefin Sulfonate (AOS) solution and nitrogen (N₂) in outcrop Indiana Limestone at high pressure and temperature after satisfying adsorption. In the oil-free core, development of the foam generation transient period and its transition into steady-state foam was rapid for all gas fractions, where the strongest foam was obtained at 90% gas fraction. Foam properties were successfully reproduced at different gas fractions. At remaining oil saturation, foam generation and propagation were significantly delayed and were observed at a high AOS surfactant concentration (5 wt %). Persistent foams were obtained both with and without remaining oil present, which withstood pressure gradients of N₂ up to 0.5 bar/m for extended times. Therefore, if correctly designed, foam gas shut-off can be a low-cost low-risk technique to reduce problems with high GOR, gas-handling, and gas reinjections.