环脊式PDC钻头破岩机理实验研究

环脊式PDC钻头是一种采用不连续布齿原理在井底形成易破碎岩石环脊的钻头技术新思想。在不同岩性、不同岩脊尺寸等条件下,开展了针对岩脊的牙轮牙齿的单齿静压和PDC齿刮切破岩单元实验,以及针对平整表面岩石的对比实验;设计制造了全尺寸可变参数实验钻头,并进行了环脊式PDC钻头与常规PDC钻头的室内钻岩对比实验。实验研究结果表明:与平整岩样的实验相比,牙轮牙齿和PDC齿在岩脊上的切削破碎载荷和破碎比功均显著降低;在全尺寸钻头钻岩实验中,与同等布齿密度条件下的常规PDC钻头相比,环脊式钻头的破岩比功显著降低,破岩效率明显提高;环脊式PDC钻头在钻进过程中有明显的体积性破碎现象,岩屑的尺寸或粒度显著增大,有利于地质录井。

Experimental Research on the Rock-breaking Mechanism of Annular-ridge PDC Bit

The annular-ridge PDC bit is a new technological concept utilizing the method of discontinuous cutter-distribution to form breakable annular rock ridges in the bottom-hole. In this research, a series of experiments were conducted, including the unit experiments on single-tooth pressing and PDC cutter cutting in the rock of different lithology and the rock ridges with varies sizes, and contrast experiment on a flat bottom-hole was furtherly conducted. On basis of the unit experiments, an experimental PDC bit with adjustable parameters was designed and manufactured, and the drilling characteristic of the bit was contrasted with a normal PDC bit. Results of the experiment show that both the rock-breaking load and specific power of the cone-teeth and PDC cutters on the annular-ridge PDC bit obviously lowered. In the whole-bit experiment, the rock-breaking specific power of the new bit apparently lower than the normal PDC bit, while the rock-breaking efficiency obviously higher. Moreover, obvious volumetric fracture generated in the rock drilled by the annular-ridge PDC bit. Moreover, compared with normal PDC bits, sizes of the rock debris generated by the new bit much larger, so that the annular-ridge PDC bit beneficial to geological logging.