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<p>Hot dry rock (HDR) shows great potential in ensuring future energy security and improving the energy mix. However, formation conditions, such as high rock strength and large in situ stress, lead to low drilling efficiency and high breakdown pressure. Percussion drilling holds promise for enhancing rock-breaking efficiency. Meanwhile, the induced stress generates radial cracks and damages the wellbore, thereby reducing breakdown pressure. To simultaneously enhance the drilling efficiency and reduce hydraulic fracturing difficulty, a series of experiments and numerical simulations are conducted. Rock damage characteristics and mechanisms under varying impact velocities, rock temperatures, and bit structures are investigated. Moreover, the effects of rock damage on breakdown pressure are also evaluated. The results indicate that higher impact velocities can increase penetration depth and energy transfer efficiency while exacerbating rock damage, thus improving both drilling efficiency and hydraulic fracturing performance. Elevated rock temperatures lead to lower rock strength and greater plasticity, resulting in larger penetration depth but lower energy transfer efficiency. The cutter–rock interaction area rises at larger forward rake angle changes, which alters the direction of stress propagation. Consequently, wellbore damage is enhanced. In this study, a forward rake angle of 20° is found to balance drilling efficiency and wellbore damage. Results obtained with spherical cutters validate that simultaneously increasing impact velocity and cutter–rock interaction area is an effective approach for enhancing wellbore damage. The combined effects of induced tensile stress and tensile damage during percussion drilling can efficiently reduce breakdown pressure, thereby facilitating the hydraulic fracturing process. This study provides new insights for the further optimization of percussion parameters.</p>

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Mechanisms and Regulation Methods of Damage in Bottomhole and Wellbore Rocks During Percussive Drilling

  • 期刊论文

  • 发表日期：

    2026年8月3日

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  • Xianwei Dai,
  • Pengju Chen,
  • Lingchao Xuan,
  • Jiawei Wang

摘要

Hot dry rock (HDR) shows great potential in ensuring future energy security and improving the energy mix. However, formation conditions, such as high rock strength and large in situ stress, lead to low drilling efficiency and high breakdown pressure. Percussion drilling holds promise for enhancing rock-breaking efficiency. Meanwhile, the induced stress generates radial cracks and damages the wellbore, thereby reducing breakdown pressure. To simultaneously enhance the drilling efficiency and reduce hydraulic fracturing difficulty, a series of experiments and numerical simulations are conducted. Rock damage characteristics and mechanisms under varying impact velocities, rock temperatures, and bit structures are investigated. Moreover, the effects of rock damage on breakdown pressure are also evaluated. The results indicate that higher impact velocities can increase penetration depth and energy transfer efficiency while exacerbating rock damage, thus improving both drilling efficiency and hydraulic fracturing performance. Elevated rock temperatures lead to lower rock strength and greater plasticity, resulting in larger penetration depth but lower energy transfer efficiency. The cutter–rock interaction area rises at larger forward rake angle changes, which alters the direction of stress propagation. Consequently, wellbore damage is enhanced. In this study, a forward rake angle of 20° is found to balance drilling efficiency and wellbore damage. Results obtained with spherical cutters validate that simultaneously increasing impact velocity and cutter–rock interaction area is an effective approach for enhancing wellbore damage. The combined effects of induced tensile stress and tensile damage during percussion drilling can efficiently reduce breakdown pressure, thereby facilitating the hydraulic fracturing process. This study provides new insights for the further optimization of percussion parameters.