Experimental Study on Rock Crack Characteristics of PDC Cutter in the Process of Rock Breaking
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摘要:
PDC齿是PDC钻头的重要破岩单元,其破岩过程包含压入和旋转切削,但现有研究忽略了压入过程的岩石损伤。为了研究PDC齿压入岩石的能力和探究岩石损伤机理,为PDC钻头的参数选择提供理论依据,采用室内试验方法研究了不同前倾角PDC齿压入青砂岩、花岗岩的破岩过程,采用岩石无损显微检测技术分析了岩石宏观及细观的裂纹。研究表明,砂岩的破碎方式为细小砂粒和黏结物的脱落,花岗岩的破碎方式为晶体的脆性破碎。岩石受载后会先在岩石内部薄弱地方萌生出单一的微裂纹,微裂纹连贯扩展形成主裂纹,主裂纹持续扩展形成宏观可见的裂纹;主裂纹附近为薄弱区域,其内部包含很多尚未成形的微裂纹;接触区域的齿尖处为应力集中区,主裂纹沿此开裂。岩石损伤过程随着前倾角的变化而变化,20°前倾角PDC齿压入青砂岩的能力最强,25°前倾角PDC齿压入花岗岩的能力最强;压入深度小于4 mm时,5°前倾角PDC齿压入岩石的能力最差。研究结果对于揭示岩石的细观与宏观损伤机理、建立PDC钻头破岩的评价方法和优化PDC钻头的设计参数及工作参数等具有重要作用。
Abstract:Polycrystalline diamond compact (PDC) cutters are an important rock-breaking unit of PDC bits, which include indentation and rotary cutting in rock breaking process. However, existing studies ignore the rock damage during indentation. The objective of this paper is to investigate the indentation ability of PDC cutters into the rock and explore the mechanisms of rock damage. This study aims to provide a theoretical basis for the parameter selection of PDC bits. The rock-breaking process of PDC cutters with different rake angles pressed into blue sandstone and granite was studied by laboratory test methods. Macroscopic and mesoscopic cracks in the rock were analyzed using non-destructive microscopic detection technology. The study found that the crushing of sandstone was caused by the falling off between fine sand particles and the binder, and the crushing of granite was manifested as the brittle fracture of crystals. After the rock was loaded, a single micro-crack would first appear in the weak part of the rock, and the micro-crack would continuously expand to form a main crack. The main crack would continue to expand to form a macroscopic and visible crack. The part near the main crack would become a weak area containing many micro-cracks that have not yet formed. The cutter tip in the contact area was the stress concentration area, and the main crack was developed along this area. The process of rock damage varies with the rake angle. The ability of PDC cutter with a rake angle of 20° to press into blue sandstone is the strongest, and the ability of PDC cutter with a rake angle of 25° to press into granite is the strongest. PDC cutter with a rake angle of 5° and an indentation depth of 4 mm had the worst ability to press into the rock. The research results are of great significance for revealing the mesoscopic and macroscopic damage mechanisms of rock, establishing the evaluation method of PDC bits for rock breaking, and selecting and optimizing the design and working parameters of PDC bits.
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Keywords:
- PDC cutter /
- rock breaking mechanism /
- crack /
- macroscopic damage /
- mesoscopic damage
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表 1 试验岩样主要的物理力学性质参数
Table 1 Main property parameters of rocks
岩性 抗压强度/MPa 弹性模量/GPa 泊松比 抗拉强度/MPa 黏聚力/MPa 内摩擦角/(°) 密度/(g·cm−3) 青砂岩 25.54 4.05 0.30 1.63 18.64 40.69 2.23 花岗岩 148.45 11.81 0.25 3.34 26.28 56.68 2.66 -
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