基于离散元法的砾岩地层三棱齿切削破岩数值模拟

三棱齿因具有强抗冲击性与高耐磨性,可提高PDC钻头在砾岩地层中破岩效率及寿命,但在砾岩地层中的破岩机理及破岩效果不明确,导致砾岩地层中三棱齿PDC钻头设计缺乏理论依据。针对上述问题,基于离散元法建立了三棱齿切削破碎砾岩的数值仿真模型,研究不同砾石与胶结物基质黏结强度差情况下砾岩破岩形式与过程,并分析了三棱齿直径及后倾角对三棱齿切削力及砾岩破碎过程中岩石裂纹拓展的影响。结果表明:在黏结强度差大于70 MPa时,砾石会直接被剥离,而强度差小于40 MPa时,砾石直接被破碎;2种黏结强度差情况下,三棱齿直径为16 mm,后倾角为15 °时,切削破碎砾岩效率均能达到最高。该研究对三棱齿PDC钻头设计具有理论意义。

Numerical Simulation of Rock Breaking by Triangular Prismatic Cutter in Conglomerate Formation Based on Discrete Element Method

Due to its strong resistance to impact and wear, triangular prismatic cutter grants PDC bit with better rock-breaking efficiency and longer service life when it is used in conglomerate formation, but the rock-breaking mechanism and rock-breaking effect in conglomerate formation are not clear, resulting in a lack of theoretical support for the design of the PDC bit with triangular prismatic cutter which is used in the conglomerate formation. A numerical simulation model of conglomerate breaking by triangular prismatic cutter was established based on the discrete element method to study the conglomerate breaking mode and process under the condition of different bonding strength between conglomerate and cement matrix, and to analyze the effect of diameter and back rake angle of triangular prismatic cutter on the cutting force of triangular prismatic cutter and the propagation of rock cracks during conglomerate breaking. The results showed that the conglomerate was directly stripped at a bonding strength difference of more than 70 MPa, while it was directly broken at a bonding strength difference of less than 40 MPa; the conglomerate cutting and breaking efficiency was maximized at a triangular prismatic cutter diameter of 16 mm and a back rake angle of 15 ° for both bonding strength differences. The study is theoretically significant for the design of PDC bit with triangular prismatic cutter.