Advances in micro-nano scale seepage in unconventional reservoirs: Experiments, simulations, and modeling perspectives

The global energy landscape is undergoing a strategic shift toward unconventional oil and gas resources, which are predominantly hosted in complex multiscale pore systems dominated by micro- and nanoscale pores. A major bottleneck to their cost-effective development lies in the limited understanding of hydrocarbon transport mechanisms at these scales. This review begins with a systematic assessment of pore network structures in unconventional reservoirs, categorizing current pore characterization techniques according to their strengths in qualitative identification and quantitative analysis. Accurate description of pore morphology and connectivity is emphasized as the foundation for both physical experimentation and numerical simulation of microscale and nanoscale flow. The review then highlights the unique transport phenomena and phase behaviors that emerge under nanoscale confinement from a molecular mechanistic perspective. In such restricted environments, oil-gas two-phase systems display distinct physical characteristics and phase transitions-such as gas rarefaction, oil-phase interfacial effects, and vapor-liquid equilibria-that deviate substantially from macroscopic behavior. Finally, the review surveys the state of physical and computational modeling approaches for micro- and nanoscale flow, analyzing their respective advantages and limitations to inform the development of systematic transport models. We conclude that future models for unconventional resource development must incorporate multiphysics and multiscale effects, including complex stress fields, pore structure heterogeneity, and multiphase interactions. Such integrative frameworks will underpin the construction of predictive mathematical models for oil, gas, and water transport in confined porous media, thereby advancing the efficient exploitation of unconventional reservoirs.