Experimental study on fractures quantitative characterization of shale during uniaxial compression

Introduction Fractures are crucial to the development of shale oil and gas because they operate as a seepage pathway. The key to ensuring effective development is the fractures strong connection. Therefore, it is of great significance to carry out experimental research on the development of shale fractures. Methods This research thoroughly assesses the quantitative features of shale fractures using a number of criteria by combining the indoor uniaxial compression test with 3D CT reconstruction. Results and discussion The findings indicate that the bedding angle has a significant impact on the distribution characteristics of shale fractures and that its quantitative features cannot be well described by a single metric. The volume weight of many fractures can be used to determine the new fracture angle and complexity coefficient, which more accurately reflect the actual fracture distribution given the complexity of fracture growth under 3D reconstruction. The connectivity examination also shows that the axial shear and radial tensile mixed fractures have higher connection than the single shear fracture, suggesting that the radial tensile fracture may lead to a higher overall connectedness. The parameters (fracture rate, fracture complexity coefficient, connectivity) used in this paper have a good correlation with the fractal dimension correlation coefficient R2 > 0.7, which indicates that these parameters are suitable parameters for quantitative characterization of shale fracture distribution characteristics. The influence mechanism of bedding angle on shale fractures is also suggested based on experimental results and earlier research. This mechanism is that the bedding angle will alter the effect of principal stress on interlayer micro-pores, micro-fractures, and cementation of bedding planes, leading to a significant anisotropy of fracture morphology created by macroscopic fracture.