Investigation on pH and redox-trigged emulsions stabilized by ferrocenyl surfactants in combination with Al2O3 nanoparticles and their application for enhanced oil recovery

Pickering emulsions are regarded as promising chemical flooding agents to control profile in enhanced oil re-covery (EOR). Stimuli responsive Pickering emulsions are introduced to simplify the process of subsequent demulsification. In the present work, we construct pH and redox-triggered emulsions stabilized by oxidized 1,1 '- ferrocenedicarboxylic acid-(N,N-dimethyldodecylamine)2 (FDA-(DMDA)2-Ox) and Al2O3 nanoparticles. Stable emulsions with low water separation rate (18.5 %) after 12-day storage can be obtained by combining a low concentration of FDA-(DMDA)2-Ox (< 0.07 wt%) and Al2O3 nanoparticles. The emulsions can undergo the conversion of emulsion type (from oil-in-dispersion emulsions to oil-in-water Pickering emulsions) triggered by pH (surface charge switchability of Al2O3 nanoparticles) and emulsification/demulsification switchable behav-iors triggered by redox reaction (redox response of FDA-(DMDA)2-Ox). The switch mechanism is revealed via the measurements of optical micrographs, zeta potential, cyclic voltammetry curves, and interfacial tension. Micromodel tests display that both oil-in-dispersion emulsions and oil-in-water Pickering emulsions can improve the displacement efficiency and enhance the sweep efficiency respectively to greatly enhance oil recovery. The pH and redox responsive flooding fluid display promising adaptability to complicated reservoir conditions and convenient implement for subsequent demulsification, transportation and refining