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

Due to their unique properties, surfactants have beenwidely usedas effective chemical additives for enhanced recovery in shale reservoirs.However, despite extensive research on the spontaneous imbibitionof surfactant solutions in shale reservoirs, the underlying mechanismsof surfactants for improving the shale wettability, reducing the flowresistance, and expanding the relative permeability still need tobe studied. This study reports the successful construction of an anionic/nonionicsurfactant mixture named LMEA-DPS (LMEA = laurel monoethanolamide;DPS = N-decyl-N,N-dimethyl-3-ammonio-1-propane sulfonate) and interfacial propertiesbetween crude oil and LMEA-DPS, including interfacial tension(IFT) reduction, wettability alteration, and emulsification ability,were investigated. The imbibition efficiency of LMEA-DPS underdifferent conditions was also explored, and the oil utilization andthe oil distribution in the rock pores were evaluated by using thenuclear magnetic resonance (NMR) technique. Experimental results showedthat LMEA-DPS exhibited superior IFT reduction, wettabilitymodification ability, and an emulsification viscosity reduction effectcompared to brine. The imbibition recovery of LMEA-DPS displayeda trend of increase and decrease with increased permeability witha more remarkable imbibition recovery for smaller crude oil viscosities.NMR analysis further revealed that macropores were the main pore spacesdeveloped in the rock and contributed the most to the imbibition recoveryefficiency. In addition, the imbibition of LMEA-DPS initiallytook place in macropores before moving into mesopores and micropores.This study also proposed efficient imbibition mechanisms of anionic-nonionicsurfactants in shale reservoirs, including IFT reduction, alteredwettability, and emulsion imbibition.