Experimental study of microscopic fracture characteristics of shale reservoirs

For shale reservoir reform it is critical to connect a larger reservoir volume by developing complex fracture network. Microscopically, however, the characteristics of fracture plane in shale reservoir affect the conductivity of self-propping fractures, and the microfractures formed on the fracture plane affect the permeability of shale gas. These aspects are equally important for shale reservoir stimulation. In this paper, the mineral composition and fracture test is conducted firstly for a series of shale samples taken from the Sichuan Basin and Jiyang Depression, and then a 3D laser scanner is used to scan the fracture planes in a group of samples, so as to analyze the flatness of such planes. Next, a scanning electron microscope is used to scan the fracture planes in two groups of samples at different multipliers to analyze the microscopic characteristics of the fracture surfaces. The results show that, higher the calcite content, stronger the fracture planes’ regularity on the contour chart, and more easily the formation of microfractures in the fracture plane; shear fracture is more possible in case of lower clay content and higher content of quartz and calcite. These conclusions are significance for understanding the fracture characteristics of shale reservoir and guiding the fracturing design.