新型随钻取心钻头破岩提速工作机理

为了获得既能随钻取得岩心又不降低机械钻速的新型钻头,基于前人的研究成果和现有的设计方法,结合随钻取心钻头的结构与破岩特点,设计出了一款全新的随钻取心钻头,并利用台架实验与现场实验对其破岩特性、机械钻速进行测试,将测试结果与理论计算结果进行对比分析。结果表明:(1)新型钻头通过在钻头内部设计一个射流专用通道,经射流喷嘴流出的高压钻井液经过吸附通道产生负压作用,将携带所取岩心进入推送通道回到环空;(2)新型钻头提速增效的效果非常明显,在排量为25 L/s的现场实验中,其提速效果介于5%~40%;(3)实验室测试与现场实验新型钻头的破岩性能与理论计算结果吻合,验证了其可靠性。结论认为,新型钻头在破岩过程中具有"吸附下部岩屑、推送上部岩屑"的效果,可降低岩屑重复破碎率,提速增效效果显著。

Rock breaking and ROP improvement mechanisms of a new CWD drill bit

In order to achieve the CWD (coring while drilling) without affecting the ROP (rate of penetration), it is necessary to develop a new CWD drill bit. In this paper, a new CWD drill bit was designed based on previous research achievements and existing design methods, combined with the structure of a CWD drill bit and rock breaking characteristics. Then, its rock breaking performance and ROP were tested in bench tests and field tests. Finally, the test results and the theoretical calculation results were compared and analyzed. And the following research results were obtained. First, a dedicated jet channel is designed inside the new drill bit. The high-pressure drilling fluid that flows out of the jet nozzle generates negative pressure effect while passing through the adsorption channel, to carry the cored rock to the push channel and then to the annulus. Second, the new drill bit is quite remarkable in ROP improvement. The ROP is increased by 5–40% in field tests with a displacement rate of 25 L/s. Third, the rock breaking performance of the new drill bit in laboratory tests and field tests is coincident with the theoretical calculation results, verifying its reliability. It is concluded that the new drill bit has the effect of "entraining the lower cuttings and pushing the upper cuttings" in the process of rock breaking and it can reduce the repeated cutting breaking rate and significantly improve the ROP and efficiency.