硬岩地层PDC钻头不良工况原因分析与改善措施

Reason analysis and improving measures of PDC bit in hard formations under bad working conditions

传统PDC钻头在硬岩地层钻进时,不良工况多,钻头寿命及钻进效率非常低。为了找出硬岩地层PDC钻头不良工况发生的原因,以四川元坝地区须家河组致密砂岩为例,建立单个PDC复合片切削岩层的模型,分别对模型中复合片及微小岩块进行受力分析,发现单个复合片受力随切入岩石弧长、岩石的内摩擦角及黏聚力的增加而增加。视所有复合片破岩的临界钻压及扭矩为整个钻头受到岩石的作用力,钻头受力超出转盘的输出钻压及扭矩会导致不良工况的发生。最后,从提高PDC钻头结构使其能适应硬岩钻进,及使用PDC钻头伴侣来改善PDC钻头的切削条件两方面提出了PDC钻头不良工况的改善措施。

When drilling in hard formations with conventional PDC bit, bad working conditions are often encountered, and life of bit is very short and drilling efficiency is very low. In order to find out reasons about bad working conditions of PDC bits in hard formations, the mechanical model of single PDC bit acting on rock formation was established based on compacted sandstone of Xujiahe Formation in Sichuan Yuanba area. Force analysis about PDC and small rock was carried out. It＇s found out that loads on single PDC was increased with the increase of the plunged arc length of PDC in rock, the internal friction angle and the internal cohesion of rock. Regarding the critical bit pressure and torque as the force of bit from rock, bad wording conditions occured when the whole force PDC bit exceeds bit pressure and torque from rotary disk of drilling machine. Finally, some improving measures about bad working conditions of PDC bit are summarized from two aspects, namely, enhancing structure of PDC bit to accommodate with hard rock, and employing partners of PDC bit to optimize the working conditions of PDC bit.