A new laboratory study on alternate injection of high strength foam and ultra-low interfacial tension foam to enhance oil recovery

Ultimate oil recovery depends on both macro sweeping efficiency and micro displacement efficiency. Foam flooding is an important method to enhance oil recovery (EOR) after water flooding. Composed of one surfactant, a traditional foaming agent generates stable foam with gas or air to block high-permeable swept zones and to improve the sweeping efficiency without significantly improving displacement efficiency. In this paper, we present a newly designed technology of alternate flooding through high strength foam (HSF) and ultra-low interfacial tension foam (ULT) to enhance oil recovery. HSF foam generates large, stable bubbles in presence of oil, beneficial to block high permeability areas; ULT foam generates small bubbles and reduces the oil-water interfacial tension to ultra-low grade. In the experiments of three parallel sand packs, the HSF foam generated with surfactant GINF-1/air could block the large pores and improve sweeping efficiency, and the ULT foam generated with surfactant LINF-2/air could improve the displacement efficiency in swept zones after water flooding. Both experimental results in parallel sand pack and 3-D sand pack show that the HSF and ULT foam alternate flooding can improve not only sweeping efficiency but also micro oil displacement efficiency, and the foam alternate flooding can realize a high oil recovery than HSF or ULT foam flooding separately. The experimental study also shows that the two foams should be alternatively injected in foam flooding of heterogeneous reservoirs, in a sequence is that HSF foam slug is applied first before using the ULT foam slug. Moreover for a given total volume of foam, a higher oil recovery is obtained through properly decreasing the volume of each foam slug and increasing the number of alternate stages.