# Study on Explosive Fracturing Mechanism of Qianjiang Shale Oil
## 3 Results and Discussion
### Blasting Damage Simulation Process
For instance, measurement points E and F, located near the borehole, respond to the stress wave earlier than points A and J, which are situated at the farthest end of the borehole. Initially, all measurement points experience compressive stress, but over time, the stress state transitions to tensile stress. According to the dynamic tensile characteristics of the reservoir rock, if the peak tensile stress remains below the dynamic tensile strength of the rock, the reservoir rock will remain intact; otherwise, cracks or even fractures may develop within a certain range. Figure 6: Theta-stress distribution curves at various radial distances for each measurement point. A–J indicates the monitoring points. Compared to Y-stress and effective stress, the vibration velocity at the measuring points provides a more direct representation of the dynamic response of reservoir rock during blasting analysis. As illustrated in Figure 8, immediately following explosive initiation, each measuring point initially moves away from the explosion source. The D-G measuring point is sequentially damaged by the explosion stress wave, resulting in values dropping to zero. For other measuring points at equivalent distances from the blast hole, the waveform curves exhibit similar patterns, showing an oscillatory trend with sequential wave peaks. The amplitude decreases as the distance between the measuring points and the blast source increases, which clearly demonstrates the symmetric propagation of the explosion stress wave and aligns with the observed attenuation of vibration velocity caused by these waves. The damage and fracture development of rock mass are the consequence of the synergistic effects of compressive stress, tensile stress, and explosive gases on reservoir rock during blasting operations. In the crushing zone, the predominant form of rock mass damage is attributed to compressive stress, whereas in the circumferential fracture zone, tensile stress plays a dominant role. As illustrated in Figure 9, the initiation, propagation, and coalescence of fractures induced by the explosive, along with the propagation of the explosion-induced stress wave through the fractured rock at various time intervals, are depicted. Figure 8: Vibration velocity time history curve. A–J indicates the monitoring points. Figure 7: Stress–time history curve. A–J indicates the monitoring points. At t = 9.9229 \(\upmu\)s (Figure 9a), immediately following explosive initiation, the generated shock wave directly impacted the borehole wall, causing localized compressive damage to the surrounding rock. Subsequently, the combined effects of compression and shear stresses led to the formation of a crush zone adjacent to the borehole wall, where the strain exceeded the predefined threshold. By t = 459.68 \(\upmu\)s (Figure 9b), the crush zone was fully developed. At this stage, the initial shock wave had attenuated into a stress wave that continued to propagate forward. Although the stress wave's intensity remained below the rock's compressive strength, insufficient to cause further crushing, it induced tensile stresses that initiated radial cracking outside the crush zone, marking the onset of the crack zone. At t = 819.81 \(\upmu\)s (Figure 9c), the crush zone ceased expanding while the main fractures began to propagate. Notably, fracture propagation lagged behind the stress wave, which had already reached the non-reflective boundary. By t = 1219.9 \(\upmu\)s (Figure 9d), fractures around the borehole continued to extend independently, with secondary branching fractures developing within the main fracture network. At t = 1989.3 \(\upmu\)s (Figure 9e), most cracks between blast holes coalesced, with only a few continuing to spread in irregular directions without merging. As the explosion-induced stress waves propagated, the cracks in the rock gradually extended. Finally, at t = 2500.6 \(\upmu\)s (Figure 9f), the fractures had fully developed throughout the model, reaching their final configuration.