Significance of the dynamic stress perturbations induced by hydraulic fracturing
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2018 Elsevier B.V. Hydraulic fracturing and microseismicity generation and radiation are dynamic processes. The associated dynamic stress perturbations could play a significant role in relevant studies, such as activation of weak planes including natural fractures, bedding planes, etc. We study how different the dynamic and static stress perturbations could be during hydraulic fracturing. Our work is based on a 2D plane-strain framework. A dynamic finite element method is applied to solve the equations of motion. The static stress perturbations are obtained when the models reach static equilibrium (i.e., after generated seismic waves die out). We compare the static and dynamic stress perturbations at a moment when a hydraulic fracture (HF) propagates to a certain length. Mohr circle analysis shows that around the HF the Mohr circle based on a dynamic stress tensor is closer to a failure line than that based on a static stress tensor. The peak static and dynamic stress perturbations during the process are also compared. We conclude that the absolute values of the peak dynamic stress perturbations are always greater than that of the peak static stress perturbations, especially in the area close to the HF and its tips. The effect of injection rates on the static and dynamic stress perturbations is also studied. The largest peak static and dynamic stress perturbations during the hydraulic fracturing process are measured. The absolute values of both the largest peak dynamic and static stress perturbations increase with injection rates. The absolute values of the difference between the largest peak dynamic and static stress perturbations also increase with injection rates due to more significant dynamic effects.
