From fundamental mechanisms to applications and challenges of nanofluid flooding in enhanced oil recovery: A review

• An overview of research statistics about different types of nanoparticles flooding. • Evaluation methods, mechanisms, and influencing factors of nanofluid stability are summarized. • Mechanisms behind nanofluids in enhanced oil recovery are introduced. • Discussion of the field application, challenges, and future prospects. Nanofluid flooding technology has shown great potential in enhancing oil recovery (EOR) of unconventional oil and gas resources. However, due to the complex physical and chemical properties of nanofluids and the complex mechanism in the harsh reservoir environment, the research and application of nanofluids still face many difficulties. Therefore, it is necessary to review the latest research on nanofluids. This paper reviews laboratory studies of different types of nanomaterials for EOR, with particular attention to SiO 2 , TiO 2 , Fe 3 O 4 , and carbon-based nanomaterials. The evaluation methods, stability mechanisms, and influencing factors of nanofluid stability are summarized. The mechanism of nanofluid EOR is discussed in detail, including structural disjoining pressure, wettability alteration, interfacial tension reduction, mobility ratio reduction, log-jamming effects, and pressure-reducing and injection-enhancing. Field trials in China, Colombia, Saudi Arabia and Japan were described. In addition, the challenges and future research directions in nanofluid EOR are also discussed. This paper will provide theoretical support for the laboratory studies and field applications of nanofluids, and aims to assist researchers in further advancing nanofluids EOR.