Abstract
Natural fractures (NFs) and bedding planes (BPs) are well developed in shale reservoirs. The propagation of hydraulic fractures (HFs) and the opening of NFs and BPs can produce induced stress fields (ISFs) within the fracturing process, causing interference to the in situ stress field. Aiming at the "stress shadow" effect among HFs in horizontal wells, the calculation models of HFs, BPs, and NFs for induced stress distributions are established based on displacement discontinuity theory, which can quantitatively characterize the composite ISF of the three under different connecting states. In addition, the interference coefficient of stress intensity factor (ICSIF) is introduced to quantitatively evaluate the interference degree of the composite ISF to the propagation of HFs. The results show that: (1) the ISF forms a "tensile stress concentration zone" near the fracture surface to promote the HFs opening and a "compressive stress concentration zone" at the fracture tips to suppress the propagation of HFs; (2) the ISF forms an elliptical effective swept area around the fracture, which is affected by the propagation height of HFs, while NFs or BPs generate local disturbances to the ISF; (3) the in situ stress reverses in the swept area, and the stress reversal interval is related to the in situ stress difference, fracture propagation height, Poisson's ratio, fracture net pressure, and fracture spacing; (4) the reasonable fracture spacing and fracture propagation height of horizontal wells can be determined by the ICSIF. The study can provide theoretical guidance for optimizing the fracture spacing and promoting the uniform propagation of multiple fractures in staged fracturing of horizontal wells.