Experimental study on the optimization and stability of methane foam systems under high-temperature, high-pressure, and high-salinity conditions

Natural gas foam flooding has good fluid control and formation blockage capabilities, but the high-temperature, high-pressure, and high-salinity environment puts forward higher requirements for the comprehensive performance of natural gas foam. The impact of different gas types on the overall performance of the foam system was evaluated via a high-temperature, high-pressure visual foam stirrer. It is found that nitrogen foam systems have strong stability but weak foaming ability, while carbon dioxide foam systems exhibit strong foaming ability but poor stability. The methane foam system showed relatively better and balanced foaming ability and stability, making it more suitable to oil fields. Ten surfactants were screened and the results indicated that α-olefin sodium sulfonate (AOS14, AOS12) and sodium dodecyl sulfate formed natural gas foam systems with better overall performance with methane. The effects of temperature, pressure, surfactant concentration, and foam stabilizers on the comprehensive performance of the methane-AOS14 foam system were investigated. With increase in the surfactant concentration, the foaming ability and stability of the methane-AOS14 foam system first increase and then decrease. Higher temperatures reduced the viscosity of the surfactant solution and decreased the interfacial tension between solution molecules, weakening the overall performance. Increased pressure facilitated the generation of denser foam with smaller diameters, slowing the liquid loss from foam films and enhancing the overall performance. Under high-temperature, high-pressure, and high-salinity conditions, polymer-based foam stabilizers enhanced the stability of the methane-AOS14 foam system by forming a spatial network structure on the foam film, with higher molecular weight yielding better effects.