The Mechanism of Three-Dimensional Hydraulic Fractures Propagation in Interbeded Shale

Shale gas reservoirs in Southern Sichuan Basin are characterized by well-developed bedding and complex tectonic stress regime, which result in the limitation of hydraulic fracture height and the efficient development of shale gas resources. By using the unique experimental technology of ultra-large scale hydraulic fracturing combined with the strain optical fiber (DSS) diagnosis technology, a full three-dimensional numerical model of hydraulic fracturing based on discrete lattice theory is established and optimized. Then the fracture vertical propagation morphology and the influencing factors in strike-slip shale gas reservoirs with beddings are simulated. The results show that: (1) there are five types of fracture height: “1”, “丰”, “T”, “十” and “工”, which correspond to totally uncontrolled, slightly controlled, partially controlled and completely controlled modes. The shape of “T” and “十” belong to partially controlled mode. (2) The main controlling factor affecting fracture vertical propagation is the cement strength of bedding, followed by beddings spacing (development), vertical stress, fluid viscosity and pumping rate, but the influence degree of the last four factors on fracture height is similar. (3) There are obvious logarithmic relationship between the fracture height and the beddings development and a power exponential relationship between the fracture height and the cement strength of bedding, which can be used for analytical prediction of the fracture height. The innovation of this paper is the development of a discrete element simulation method for hydraulic fracturing that takes into account the shale beddings. It is important guarantees for accurately understanding the hydraulic fracture propagation in the shale gas reservoirs and optimizing the design of corresponding processes.