Interfacial Properties and Efficient Imbibition Mechanism of Anionic–Nonionic Surfactants in Shale Porous Media

Abstract

Due to their unique properties, surfactants have been widely used as effective chemical additives for enhanced recovery in shale reservoirs. However, despite extensive research on the spontaneous imbibition of surfactant solutions in shale reservoirs, the underlying mechanisms of surfactants for improving the shale wettability, reducing the flow resistance, and expanding the relative permeability still need to be studied. This study reports the successful construction of an anionic/nonionic surfactant mixture named LMEA−DPS (LMEA = laurel monoethanolamide; DPS = N-decyl-N,N-dimethyl-3-ammonio-1-propane sulfonate) and interfacial properties between crude oil and LMEA−DPS, including interfacial tension (IFT) reduction, wettability alteration, and emulsification ability, were investigated. The imbibition efficiency of LMEA−DPS under different conditions was also explored, and the oil utilization and the oil distribution in the rock pores were evaluated by using the nuclear magnetic resonance (NMR) technique. Experimental results showed that LMEA− DPS exhibited superior IFT reduction, wettability modification ability, and an emulsification viscosity reduction effect compared to brine. The imbibition recovery of LMEA−DPS displayed a trend of increase and decrease with increased permeability with a more remarkable imbibition recovery for smaller crude oil viscosities. NMR analysis further revealed that macropores were the main pore spaces developed in the rock and contributed the most to the imbibition recovery efficiency. In addition, the imbibition of LMEA− DPS initially took place in macropores before moving into mesopores and micropores. This study also proposed efficient imbibition mechanisms of anionic−nonionic surfactants in shale reservoirs, including IFT reduction, altered wettability, and emulsion imbibition.