Nanomaterials in EOR: A Review and Future Perspectives in Unconventional Reservoirs

With escalating global energy demands and the depletion of conventional oil reserves, the exploitation of unconventional oil reservoirs necessitates advanced recovery materials. Nanomaterials, due to their substantial surface-to-volume ratio and elevated surface energy, emerge as potential solutions to the challenges of ultralow permeability and intricate pore structures in these reservoirs. Despite copious laboratory research on nanosolid particles, nanosurfactants, and nanoemulsions, field data regarding their use in unconventional reservoirs remains scarce, hindering the development of a selection mechanism for optimal nanomaterial utilization across different production stages. Consequently, an exhaustive investigation into the characteristics, mechanisms, and field trial data of nanomaterials is paramount for enhancing recovery rates and economic efficiency and guiding the broader application of these materials in unconventional reservoirs. Therefore, this work reviews the characteristics and pros and cons of various nanomaterials in application. It elucidates several mechanisms of nanomaterials in enhancing recovery rates, such as increasing the viscosity of the injection fluid, reducing interfacial tension, changing rock wettability, especially altering oil flow, promoting spontaneous imbibition and expanding sweep efficiency. Furthermore, the paper also integrates the field application cases of the independently developed nanoemulsion in unconventional oil areas of shale in Xinjiang and tight oil in Jilin, China, to emphasize and illustrate the importance of matching different nanomaterials according to different stage extraction characteristics. Finally, this work looks forward to future research, advocating for a deeper understanding of the behavior of nanomaterials in unconventional oil reservoirs through the combination of physical and numerical simulation experiments, to optimize their performance and applicability in a wider industrial environment.