DYNAMIC FRACTURE PROPAGATION EXPERIMENT IN HYDRAULIC FRACTURING BASED ON HIGH-FREQUENCY GRATING MONITORING

The propagation behavior of hydraulic fractures directly determines the effectiveness of reservoir stimulation and the potential for production enhancement, which constitutes a core scientific problem in the design and optimization of fracturing engineering. Accurate characterization of this dynamic evolution process therefore holds profound theoretical value and substantial practical significance. This study proposes an experimental method for monitoring the dynamic evolution of hydraulic fracturing fractures based on high-frequency Fiber Bragg Grating (FBG) technology, which effectively addresses the critical technical challenge that traditional monitoring means face in capturing the dynamic characteristics of fracture propagation in real time. In true triaxial fracturing experiments, a high-frequency FBG sensor array was strategically embedded within the rock specimen, and both strain and strain rate response signals were systematically acquired at different sampling frequencies of 10 Hz, 100 Hz, and 1000 Hz. The experimental results demonstrate that high-frequency monitoring at 1000 Hz can clearly identify the pressure accumulation near the wellbore, the development and progressive accumulation of damage prior to fracture initiation, thereby revealing the fundamental mechanical mechanism that governs rock damage and rupture in the near-wellbore region. Furthermore, through comparative analysis of the propagation behaviors between curved and planar fractures, it is found that with increasing tortuosity of curved fractures, they exhibit significantly more pronounced localized transient strain response enhancement during propagation, which are characterized by strain rate spikes that become progressively more frequent and of substantially greater amplitude, clearly indicating a significant enhancement of the local strain response intensity during the fracture deflection process.. This study validates the high-resolution advantages of high-frequency FBG monitoring technology in identifying fracture propagation stages and discriminating fracture morphology, and further reveals the correlation between strain response and fracture morphology during hydraulic fracturing fracture propagation, thus providing experimental evidence for laboratory-scale investigation of non-planar fracture propagation and for the design of fracturing monitoring methods.