In Jilin Oilfield, development of water-flooding operations in tight oil reservoirs is not satisfactory due to low effective permeability, tiny pore throats, and low mobility of crude oil in the matrix. In the interest of improving water-flooding efficacy for tight oil reservoirs, researchers in this study developed one nanofluid permeation flooding system through microemulsion preparation. This paper presents the experiments evaluating the characteristics and mechanism of improving tight oil recovery using nanofluids. The study results demonstrate that (1) the nanofluid permeation flooding system, with an average particle size of <25 nm, is very stable under the reservoir conditions and can effectively expand the swept volume ratio of the matrix with low porosity and ultralow permeability; (2) under the flow condition, the system can split the tight oil in Jilin Oilfield into "oil droplets in nanosize" which can be easily displaced from the matrix, with both swept volume and oil displacement efficiency exceeding 90% according to the micro etching model; and (3) the system has a good interfacial activity, leading to an interfacial tension with the tight oil in Jilin Oilfield of up to 10 −1 mN/m, so that it can greatly promote the efficacy of oil displacement in the matrix with tiny pores. According to the flooding experiments with cores retrieved from the oilfield, the nanofluid permeation flooding system with a concentration of 0.3% improves the oil displacement efficiency of water flooding by more than 27% averagely and reduces the injection pressure by over 38%. NMR evaluation results of tight cores indicate that the flooding system allows crude oil to be more efficiently displaced from meso/micropores. The nanofluid permeation flooding system is presumed to effectively improve the swept volume and oil displacement efficiency of water flooding and replenish formation energy. It can be a great support for efficient water-flooding development and continuous enhanced oil recovery in tight oil reservoirs of Jilin Oilfield.

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