Modeling the interaction of hydraulic fracture with natural fracture based on lattice methods

There are many interactions between hydraulic fractures (HFs) and nature fractures (NFs) during the use of hydraulic fracturing. At present, many scholars have studied hydraulic fracture morphology in hydro-mechanical (HM) coupling. In this paper, thermal-hydro-mechanical (THM) coupling is adopted to investigate the propagation of HFs in NFs. With the purpose of exploring the effects of approach angle, friction angle, NF cohesion, and injection rates on the HF-NF interaction process, the code XSite is used to establish a new THM coupling calculation model in this paper. In addition, we calculated the tensile strength and the toughness of the rock, and the accuracy of the model was verified by tri-axial experiment. Natural fractures and hydraulic fracturing fractures mainly exhibit three different forms: they have not penetrated natural fractures, they are penetrating natural fractures, and they have penetrated NFs. The results indicate that the direction and properties of fractures have a significant influence on the interaction between HFs and NFs. Furthermore, HFs tend to penetrate NFs with large approach angle, friction angle, fracture cohesion, and injection rate, suggesting that large approach angles, friction angles, NF cohesion, and injection rates will prevent NFs from opening and thus prevent cracks from expanding in NFs. With the propagation of fractures, the pressure in the injection well increases while that in the production well decreases. As the injected fluid flows through the rock mass, the low-temperature zone of rock mass diffuses in the same direction, eventually making the temperature of the production fluid and the injection fluid basically the same.