Effects and Mechanisms of Acidic Crude Oil–Aqueous Solution Interaction in Low-Salinity Waterflooding

Abstract

Crude oil–aqueous solution interactions play an important role in low-salinity waterflooding, but their effects and mechanisms have not been well clarified. Core flooding experiments were first conducted to analyze the effects of crude oil–aqueous solution interactions on enhanced oil recovery (EOR). Then, interfacial tension (IFT) and interfacial dilatational rheology (IDR), total organic carbon (TOC), and ζ-potential measurements were combined to investigate the mechanisms of crude oil–aqueous solution interactions in low-salinity waterflooding. Core flooding results showed that crude oil–aqueous solution interactions are important in low-salinity waterflooding and that adjusting the ionic composition of the aqueous solution could affect EOR. Herein, Mg2+ and Ca2+ both had positive effects on EOR, while SO42– showed no positive effect. The IFT and IDR, TOC, and ζ-potential results indicated that the ionic composition of aqueous solutions has a great influence on crude oil–aqueous solution interactions. Thereof, Mg2+, Ca2+, and Na+ preferentially interact with acidic polar molecules and enhance crude oil–aqueous solution interactions, and the intensity is Mg2+ > Ca2+ > Na+. SO42– interacts with cations and acidic polar molecules simultaneously, consequently reducing the effects of cations on crude oil–-aqueous solution interactions in varying degrees. Therefore, the positive effects of Ca2+ and Mg2+ exceed the negative influence of SO42– in CaSO4 and MgSO4, while the negative impact of SO42– outweighs the positive effect of Na+ in Na2SO4.