(1. Beijing Energy Conservation and Emission Reduction Key Technology Collaborative Innovation Center，Beijing University of
Civil Engineering and Architecture，Beijing 100044，China；2. University of Chinese Academy of Sciences，Beijing 100049，China；3. Key Laboratory of Shale Gas and Geoengineering，Institute of Geology and Geophysics，Chinese Academy of
Sciences，Beijing 100029，China；4. Institute of Geological Survey，Pearl River Planning Survey and
Design Co.，Ltd.，Guangzhou，Guangdong 510610，China)
Abstract：Hydraulic fracturing is commonly applied into shale gas exploitation industry. However mechanical mechanism of permeability under the fracturing has been unclear so far. In view of this，a statistical analysis and discussion of the mechanical mechanism by the laboratory experiments on the hydraulic fracturing cracks propagation，and the activation of bedding plane of shale specimen are presented in the study. It is demonstrated that the microscopic observed micro-cracks could not be produced by fluid pressure as the latter generated compressive stresses on the places of micro-cracks. On the contrary，the micro-cracks are produced by tensile stress concentration in front of the propagating fracture. This implies that the bedding plane reactivation is caused by fracture propagation along the plane. An analysis of micro-crack lengths shows that shale exhibits anisotropy in fracture toughness with the resistance to fracture propagation parallel to bedding planes being as twice a small as compared with the resistance to fracture propagation in the directions normal to bedding planes.
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2023, Vol. 42 
