A comparative study of the mechanism and performance of surfactant- and alkali-polymer flooding in heavy-oil recovery

The performances of surfactant-polymer (SP) and alkali-polymer (AP) systems in recovering heavy oil were systematically compared via interfacial tension (IFT), emulsification, and oil displacement experiments. Significant differences of heavy-oil-recovery mechanism by SPs and APs are firstly revealed, those are, ultra-low IFT and oil-in-water (O/W) emulsification dominate using the former, while water-in-oil (W/O) emulsification dominates using the latter. Further more, AP (and its corresponding mechanisms) significantly outperform the SP in terms of heavy-oil recovery. Fortunately, the SPs can be improved by increasing the slug size, using preformed particle gels or bubble assistance, among which bubble-assisted ultra-low-IFT SP (foam) behaved the best. The success of AP and foam suggests two feasible routes for improving heavy-oil recovery: (i) forming W/O emulsions using alkali-containing systems; and (ii) improving ultra-low-IFT systems using profile-control agents, e.g. bubble. If the problem of scaling using alkali is considered, then the second idea may be the best option. (C) 2020 Elsevier Ltd. All rights reserved.