Taking the shale in the eastern Sichuan Basin as examples

we studied the formation and evolutionary patterns of structural fractures in shale through field observation

rock mechanics experiment

physical simulation of photo elastic and finite element simulation in combination with statistical data of development via hydraulic fracturing. It is revealed that the shale has rich deposit rhythm

pre-existing weak surfaces and strong heterogeneity. Shale bedding is the preferred structure surface for fracture development and controls the formation and evolutionary characteristics; Stress will adjust its direction when encountering shale bedding during structural deformation. The compressive stress tends to parallel weak surface

while the tension stress tends to be vertical to weak surface

which leads to weak plane opening and preferred development bedding-parallel fractures. Bedding-crossing fractures would develop when the bedding-parallel fractures are not enough to accommodate tectonic deformation. Characteristics of shale fracture distribution have sharp distinction in different locations of tectonic deformation which can be divided into five areas such as anticlinal top high angle fractures

extension of bedding-crossing fracture to bedding-parallel fracture

slip conversion

bedding-crossing fracture climbing to bedding-parallel fracture and synclinal bottom high angle fractures. It is proposed that areas with multiple sets of cap rocks overlapping is a favorable condition for exploration on structural highs

while the development and expansion of fractures is the key factor for exploration in sweet spots.