Development Model of Natural Fractures in Continental Shale of the Pingdiquan Formation in the Shuangjingzi Area,Eastern Junggar Basin
The Permian Pingdiquan Formation shale oil resources in the eastern Junggar basin are abundant,however,the exploration and development of shale oil are hindered since natural fractures serve as important storage spaces and fluid migration channels for hydrocarbons there. In this paper,the development characteristics and controlling factors of natural fractures in the Pingdiquan Formation were analyzed through detailed characterization of outcrops in the Shuangjizi area,and the distribution patterns of fractures were discussed based on these findings. The results show that the natural fractures in the Pingdiquan Formation in the Shuangjizi area of the Junggar basin include three types:bed-bounded fractures,unbounded fractures,and bed-parallel fractures,with the bed-bounded fractures being the most extensively developed and distributed. The development of natural fractures is influenced by lithology,rock mechanics layers,and structures,which is mainly manifested in:(1) the degree of development of fractures in different lithologies varies,with the most developed fractures occurring in siltstone and tuffaceous siltstone;(2) the development of fractures is controlled by rock mechanics layers,with the degree of development of natural fractures being higher in thinner rock mechanical stratigraphy;and (3) there is a fracture development zone near faults,with the degree of development of fractures being higher closer to the fault plane,on the footwall and at the end of the fault. The types and distribution characteristics of fractures differ greatly in different rock layers and structural positions,with intraformational open fractures being mostly developed in rock mechanical stratigraphy with greater brittleness,transformational shear fractures can cut through multiple sets of rock layers,and bed-parallel shear fractures mainly develop in rock layers with higher mud content. The formation and distribution of fractures are closely related to the differences in rock mechanics properties between sandstone and mudstone interbeds,as well as the thickness of mudstone interbeds.
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