Although significant progress has been made in the development of shallow natural gas, the exploitation of deep shale gas continues to face numerous challenges. Therefore, conducting research on deep shale gas extraction is crucial. The efficient exploitation is contingent upon a comprehensive understanding of the mechanical properties, fracturing behaviors, and transformation processes of deep reservoir formations. This paper initially delineates the geo-mechanical characteristics and key development challenges associated with deep shale gas reservoirs. It subsequently reviews recent advancements in laboratory experiments, numerical simulations, and field technologies. Finally, suggestions and strategies are proposed to enhance the efficiency of deep shale gas development. The perspectives offered in this paper aim to provide new insights into optimizing exploration and production in deep and complex geological environments.

The analysis of mechanical response and deformation-cracking behavior contributes to the high-efficiency extraction of geo-energy and long-term safety of underground engineering structures. Compared to natural cores, the mechanical properties of 3D-printed samples made from quartz sand as raw material are relatively homogeneous, and can be used for quantitative studies on the influence of natural defects on the mechanical properties of rocks. In this work, 3D-printed samples with single fractures of different crack angles, lengths and widths were fabricated and used for uniaxial compression tests. Adopting the digital image correlation method, the stress-strain distribution during uniaxial compression tests were visualized, and the influence of prefabricated fracture characteristics (dip angle, length, and width) on the deformation-failure process were studied. An extended finite element method subroutine for ABAQUS^® software was modeled and used for the uniaxial compression simulation, which was validated by experiments. Then, the influence of mechanical parameters (Young's modulus, Poisson's ratio, cohesion, and internal friction angle) on the deformation-cracking mechanics were simulated and studied. The results indicate that, compared to the intact sample, fractures reduce the sample strength. With the extension of fracture length and width, or the decline of fracture angle, both the peak strain and strength of the 3D-printed samples decrease. The splitting tensile failure, or shear failure, or both were determined for the 3D-printed samples with different fracture angles. For the same axial strain, the extension length of the new crack increases linearly with rising Young's modulus and decreases linearly with increasing Poisson's ratio. The initial strain of new cracks decreases linearly with increasing Young's modulus, while little variations are found in samples with different Poisson's ratio. For the same axial displacement load, the peak stress increases linearly with growing internal friction angle and cohesion.

The fracture-controlled matrix unit is commonly found in low-permeability fractured reservoirs. Due to the permeability difference between the fracture system and the matrix system, a large amount of oil will remain in the matrix during traditional water injection development, thus limiting reservoir productivity. However, the special imbibition mode of the fracture-controlled matrix unit provides a breakthrough for secondary oil recovery. In this paper, based on the model of single fracture-controlled matrix unit, the dynamic production process of fractured reservoir is studied by the numerical simulation method. The numerical simulation of the imbibition oil production is carried out on the two-point well model by using the method of huff and puff injection. The results show that imbibition is the main mechanism in the middle and late stages of oil recovery from fractured reservoirs. The water in the fracture is absorbed into the matrix by capillary force and the oil is replaced; in this way, imbibition can increase the recovery rate by 20%. The findings provide a basis for the further study of the fracture-controlled matrix unit and imbibition.