东海深部高研磨地层冲击钻井PDC齿优选研究

Optimization of PDC Cutter for Percussive Drilling in Deep Highly-Abrasive Strata in the East China Sea Basin

东海盆地深部地层机械钻速(ROP)低、PDC钻头钻齿易磨损、单个钻头进尺数少的问题日益突出。为此,开展了岩石可钻性、硬度与塑性系数、强度、研磨性及组分检测试验,明确了导致该区域深部地层低ROP的主控因素,并对ROP变化规律进行了验证;设计了冲击载荷作用下PDC钻头异形齿破岩试验装置,开展了单齿破岩试验,利用3D扫描技术量化了三棱齿、斧形齿在不同冲击速度下的侵彻深度和破岩体积,计算了冲击破岩过程中的能量吸收效率以及破岩比功,对PDC钻头异形齿进行了优选;同时结合优选结果开展了现场试验。研究结果表明:岩石的高研磨性和高强度是东海盆地低ROP的主控因素,当冲锤冲击速度小于7.1 m/s时,三棱齿侵彻深度和破岩体积更大,提速效果较为明显;当冲锤冲击速度大于7.1 m/s时,斧形齿的破岩比功要小于三棱齿,且能量吸收效率更优,在高研磨地层作用下磨损较小,能更好地延长PDC钻头的寿命;现场试验也验证了该结论。研究成果可为东海盆地深部地层冲击钻井参数的确定以及PDC钻头钻齿的优选提供有效参考。

The problems of low rate of penetration(ROP),easy wear of PDC cutters and small single-bit footage are becoming increasingly prominent in the deep strata of the East China Sea Basin.The rock drillability,hardness and plasticity coefficient,strength,abrasiveness and component detection tests were performed to clarify the main controlling factors for low ROP in the deep strata of the study area,and the results were verified by the changes in ROP.Then,a rock breaking test device for special-shaped cutters of PDC bit under impact load was designed for rock breaking test of single cutter.The 3D scanning technique was used to quantify the penetration depth and rock breaking volume of triangular and axe-shaped cutters at different impact speeds,the energy absorption efficiency and rock-breaking specific energy during the percussive rock breaking process were calculated,and the special-shaped cutters of PDC bit were optimized.Finally,field tests were conducted based on the optimization results.The results show that the high abrasiveness and strength of rocks are the main controlling factors for low ROP in the East China Sea Basin.When the impact speed of the hammer is less than 7.1 m/s,the penetration depth and rock breaking volume of the triangular cutter are greater,and the ROP improving effect is more obvious.When the impact speed of the hammer is greater than 7.1 m/s,the rock breaking specific energy of the axe-shaped cutter is lower than that of the triangular cutter,and the energy absorption efficiency is better;when it is used for drilling in highly-abrasive strata,the wear is smaller,and the service life of PDC bit can be better prolonged.The field tests also verify these conclusions.The research results provide effective references for the determination of percussive drilling parameters and the optimization of cutters of PDC bit in deep formations of the East China Sea Basin.