Mechanism of using liquid nanofluid to enhance oil recovery in tight oil reservoirs

Abstract Liquid nanofluid (LNF) has been widely used for enhanced oil recovery (EOR) in tight oil reservoirs in recent years. However, the mechanism of oil recovery by LNF flooding is still unclear. In this study, a series of experiments were conducted to explore this problem. The properties of LNF were first evaluated by testing contact angles and particle size distributions. Then, the blocking and adsorption in the matrix were investigated. After that, the imbibition with nuclear magnetic resonance (NMR) was conducted to evaluate the imbibition recovery and process. Finally, the retained permeability was studied through pressure transmission tests. Our results showed that the LNF can be transported in the nano-scale pores and pore throats without bridging in the formation. This increased sweep volume and efficiency while maintaining low adsorption. During the imbibition process, with the wettability alteration and proper interfacial tension, the LNF entered small pores first to displace oil. Moreover, when injected into the reservoir, LNF in pores could avoid the exhaustion of formation pressure to prolong the effective production period. Finally, the higher retained permeability could reduce the flow resistance and energy consumption while increasing the production indirectly. Our study has not only provided a method to evaluate a chemical fracturing fluid additive but also revealed a new mechanism of LNF flooding in tight oil reservoirs.