Experimental Investigation of Pore-scale Processes in Surfactant Flooding in Heterogeneous Carbonate Reservoirs

Summary Three-dimensional pore-scale imaging was applied to study the secondary injection of a cationic surfactant above the critical micelle concentration with no co-solvent: the oil/water interfacial tension although lowered to 6.3 mN/m, was not negligible. The rock sample underwent crude oil injection to reach a representative wettability state. The surfactant recovered 79% of the initial oil. Analysing pore and throat occupancy revealed an oil-wet system. The surfactant initially invaded and displaced oil from medium-sized and large pores of radius greater than 15 μm, with minimal impact in small pores. While subsequent injection further recovered oil from smaller pores, the tiniest ones, with radius of 5 µm or less, remained unaffected. Observations of contact angles, mean curvatures and capillary pressures indicated a transition from a weakly oil-wet to a mixed-wet state. The primary driving mechanisms behind the efficient displacement of oil are synergistic interplay of wettability alteration and interfacial tension reduction.