Visualising surfactant enhanced oil recovery

Surfactant formulations that give rise to ultra-low interfacial tensions are used to enhance the recovery of crude oil by eliminating the trapping effects of capillary forces. The formulations, when mixed with oil, often give microemulsion-type phase behaviour. Depending on the surfactant affinity for oil and water, the microemulsion may exist as water-in-oil (L2), oil-in-water (L1), or bi-continuous (L3). Here, an aqueous formulation of anionic surfactants and butan-2-ol that would give rise to Ll and L3 phase behaviours at different NaC1 concentrations is injected into decane-filled porous media. The displacement processes in rock cores are followed by spatially resolved NMR and in microfluidic models by optical microscopy. Both surfactant formulation types enhance the oil displacement from the core but the L3-forming system shows more complex behaviour, consistent with first the formation and then the displacement of microemulsion phases, which leads to significant enhancements in oil recovery. (C) 2014 Elsevier B.V. All rights reserved.