▎ 摘　　要

Current displacing agents for enhanced oil recovery (EOR), i.e., water, gas, foam, and common nanofluid, suffer plenty of problems in ultralow-permeability reservoirs, with a limited oil recovery. A novel agent, amphiphilic graphene oxide (H-GO), is confirmed to be effective in EOR under such unconventional conditions. We present the fundamental mechanisms for the improved performance by H-GO. Specifically, the effectiveness of H-GO is experimentally verified from multiple perspectives, including emulsifying ability, interfacial activity, and wettability alteration action. Experimental observations show that H-GO has excellent emulsifying ability that the amphiphilic Janus nanosheet is inclined to move onto the oil-water interface. Pickering emulsion formed by H-GO and oil, with an average droplet diameter of only 2.66 mu m, is considerably stable, which can be maintained for at least 30 days. Besides, H-GO reduces the oil-water interfacial tension to 0.493 mN/m, 1 order of magnitude lower than that between the common nanoparticle and oil. H-GO shows better wettability alteration efficiency compared to a common nanoparticle. Consistently, micromodel tests show that H-GO gives a promising sweep and displacement efficiency to oil. As a result of these advantages of H-GO, the oil on the rock surface can be separated and form the emulsion or oil zone easily, leading to the incremental recovery of 10.83% using only H-GO (1 mg/mL) in an ultralow-permeability core. The study provides a novel approach for EOR in ultralow-permeability reservoirs. The high performance, convenient operation, and environmental protection make H-GO flooding have great potential for oilfield practice.