Abstract: The development characteristics of microfractures in shale reservoirs directly control hydrocarbon seepage capacity and the effectiveness of hydraulic fracturing stimulation,and thus constitute a key geological factor for the economical and efficient development of shale oil and gas.However,microfracture systems are characterized by large-scale spans,strong spatial heterogeneity and low identification accuracy,so their precise characterization and prediction have long remained core challenges in shale oil and gas geology.In response to the problem,this study systematically reviews the current status of microfracture characterization methods,including field outcrop observation,core and cast thin-section analysis,well-log identification,gas adsorption and high-pressure mercury intrusion,and electron microscopy.It also summarizes the theoretical progress in fracture prediction methods,such as equivalent continuum models,discrete fracture network models and hybrid models,and discusses development trends in shale microfracture characterization technology.The study shows that the integration of multiple techniques and coordinated multiscale characterization is an effective way to improve the recognition accuracy of shale microfractures.In the future,a continuous and complete pore-fracture evaluation system should be established,and the combinations of fracturing fluids and proppants should be optimized so as to achieve effective support and full-scale prediction from microscopic fractures to macroscopic fracture networks,thereby promoting the intelligent and precise development of shale oil and gas exploration and exploitation.This study provides a theoretical reference for microfracture characterization and hydraulic fracturing stimulation of shale reservoirs.

Key words: shale, microfracture, fracture prediction, review