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<p>The extensive application of hydraulic fracturing in unconventional reservoirs raises new challenges in understanding the fracture mechanism of granitic materials. Triaxial hydraulic fracturing experiments were conducted to examine the influence of coarse grains on the failure behaviour of impermeable granites based on the associated seismic responses. The waveform frequencies in laboratory hydraulic fracturing are predominantly below 600 kHz, with a dominant frequency around 200 kHz. Source mechanism analysis reveals that tensile cracks constitute the largest proportion among all crack types while have smaller magnitudes than non-tensile cracks. The micro-cracks are induced prior to fracture initiation which delays the immediate macro rupture, following peak injection pressure by the dilatancy hardening effect. The tensile cracks contribute to the increase in damage volume while the non-tensile ones lead to a reduction effect. Overall, the total damage volume escalates as average grain size increases. Granites have event magnitude less than -6.0 and b-values greater than 2. Small magnitude seismic events take less dominance of proportion with increasing grain size. Larger average grain size and lower grain size heterogeneity weaken the cementation between mineral grains, triggering larger boundary cracks. These cracks result in greater offset distance between multiple fractures and increase fracture tortuosity, also leading to longer failure duration, stronger seismic detectability, and a larger slip plunge range and average degrees.</p>

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Seismic Characterisation of Hydraulic Fractures Influenced By Granitic Coarse Grains

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2025年3月10日

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  • Xin Zhang,
  • Guangyao Si,
  • Jianguo Zhang,
  • Man Wang,
  • Guozhen Zhao,
  • Joung Oh

摘要

The extensive application of hydraulic fracturing in unconventional reservoirs raises new challenges in understanding the fracture mechanism of granitic materials. Triaxial hydraulic fracturing experiments were conducted to examine the influence of coarse grains on the failure behaviour of impermeable granites based on the associated seismic responses. The waveform frequencies in laboratory hydraulic fracturing are predominantly below 600 kHz, with a dominant frequency around 200 kHz. Source mechanism analysis reveals that tensile cracks constitute the largest proportion among all crack types while have smaller magnitudes than non-tensile cracks. The micro-cracks are induced prior to fracture initiation which delays the immediate macro rupture, following peak injection pressure by the dilatancy hardening effect. The tensile cracks contribute to the increase in damage volume while the non-tensile ones lead to a reduction effect. Overall, the total damage volume escalates as average grain size increases. Granites have event magnitude less than -6.0 and b-values greater than 2. Small magnitude seismic events take less dominance of proportion with increasing grain size. Larger average grain size and lower grain size heterogeneity weaken the cementation between mineral grains, triggering larger boundary cracks. These cracks result in greater offset distance between multiple fractures and increase fracture tortuosity, also leading to longer failure duration, stronger seismic detectability, and a larger slip plunge range and average degrees.