The Roles of Micro Pores and Minerals in Shale during Hydraulic Fracturing

Hydraulic fracturing is commonly used in the stimulation of shale reservoirs for sustainable production and commercial development. The fracturing mechanisms of shale matrix, especially the roles of micro pores and minerals, is of vital importance for our understanding of hydraulic fracturing treatments. In this study, we induced hydraulic fractures in laboratory by performing hydraulic fracturing experiments, and observed two dimensional and three dimensional structures of micro-scale cracks in the shale matrix before and after hydraulic fracturing treatment using scanning electron microscopy (SEM) and focused ion beam scanning electron microscope (FIB-SEM) tests. We also counted the probability of different cracking modes and analyzed the relationships between crack pathways and the distributions of minerals, organic matters and pores. The results showed that the cracks mainly propagated along the boundaries of different minerals. The intergranular and organic pores can be captured by the induced cracks, and the intraparticle pores are hard to be reactivated. The present study provides us more evidences for further study of fracturing mechanism in shale matrix.