Prediction Research of Wellbore Fractures and the Impact on Drilling Fluid Leakage

Deep shale reservoirs in the Luzhou Block are characterized by developed fractures and complex structure. Accurate identification and characterization of natural fractures in reservoirs are crucial for shale gas exploration and development. In this paper, the main development characteristics of natural fractures in the target layer were clarified based on core observation data and imaging logging data, and then the natural fractures were identified by combining the R/S analysis method. Furthermore, due to the different orientations of different fractures, there are differences in fracture activation pressure and drilling fluid leakage, which have a significant impact on the identification of risk zones. The results showed that low-angle and east–west oriented fractures are not easily activated because their orientation relative to the maximum horizontal principal stress is unfavorable, resulting in lower shear stress on the fracture planes. Moreover, after fracture activation, the opening deformation decreases with increasing inclination, leading to differential changes in the leakage rate. The 60° inclination angle fracture is the critical value for high-risk leakage compared to the low-risk leakage. The research results can provide important guidance for further drilling optimization and development of deep shale gas in the Luzhou Block.