Interplay mechanisms between hydraulic fractures and natural fractures in various propagation regimes

It is crucial for the successful development of fractured reservoirs to understand the interaction behavior between hydraulic fractures and natural fractures. This work employed a true-triaxial fracturing experiment using prefabricated samples with natural fractures, along with a three-dimensional (3 D) numerical model, to investigate the interaction mechanisms between hydraulic fractures and preexisting natural fractures. Various influencing factors, including the horizontal stress difference, injection rate, fluid viscosity, and approach angle, are considered. The results reveal three distinct modes of interaction between hydraulic fractures and natural fractures: crossing, deflection, and arrest. As the horizontal stress difference, injection rate, and viscosity increase, the interaction between hydraulic and natural fractures undergoes a gradual shift, evolving from arrest to deflection and ultimately crossing. A smaller approach angle enhances the likelihood of hydraulic fractures being captured by natural fractures. Furthermore, the evaluation criterion of propagating ability is proposed based on the dimensionless value to facilitate the evaluation of the interplay between hydraulic and natural fractures. The interaction behavior diagrams between hydraulic fracture and natural fracture in different regimes is established. It shows that the fracture penetration capacity gradually increases from toughness-dominated regime to viscous-dominated regime, as evidenced by the phased arrangement of arrest, deflection, and crossing in their interaction with natural fractures. When the tensile strength and cohesion of natural fractures is high, hydraulic fractures tend to pass through directly, while conversely, they are easily arrested by natural fractures. The research findings can offer valuable insights for optimizing the fracturing in unconventional reservoirs with developed natural fractures.