牙轮—PDC混合钻头的破岩特性及温度场变化

较之于常规的PDC钻头或牙轮钻头,牙轮—PDC混合钻头有着更好的破岩效果,其破岩过程产生的热量对其使用寿命和钻井效率都有着重要的影响,但目前对其破岩过程中温度场和破岩特性的研究还不够深入。为了给混合钻头的优化和推广提供理论支撑,基于有限元法、弹塑性力学等建立钻头破岩仿真模型,据此研究了破岩过程中的混合钻头温度场变化规律和破岩特性。研究结果表明:(1)牙轮主导型混合钻头破碎岩石时牙轮切削结构先冲击岩石,形成破碎坑,PDC切削齿再进行剪切,而PDC主导型混合钻头由PDC切削齿对岩石进行刮切形成沟槽,牙轮切削齿再对岩石进行破碎;(2)混合钻头在破岩初始阶段温度上升较快,一段时间后趋于平稳且钻压越大温度越高;(3)较之于PDC钻头和牙轮钻头,混合钻头破岩过程中温度更低,混合钻头破岩量大于单个PDC钻头和单个牙轮钻头破岩总量之和;(4)混合钻头在硬地层中的破岩温度高于在软地层中的破岩温度,而钻速则相反;(5)钻头破岩温度和破岩特性与其自身结构有关。结论认为,该研究成果有助于混合钻头的优化设计和推广应用。

Rock-breaking characteristics and temperature field change of cone–PDC hybrid bits

Compared with a conventional PDC bit or a cone bit, a cone–PDC hybrid bit is better in rock breaking effect. The heat generated in the process of its rock breaking has a significant effect on its service life and drilling efficiency. So far, however, the temperature fields and rock breaking characteristics in the process of its rock breaking have not been researched thoroughly. In order to provide a theoretical support for the optimization and popularization of a hybrid bid, this paper established a rock-breaking simulation model based on finite element analysis method, elastic–plastic mechanics, etc. And based on this, temperature field change laws and rock breaking characteristics of the hybrid bit in the process of rock breaking were analyzed. And the following research results were obtained. First, when a cone-dominated hybrid bit is used for rock breaking, the rolling cutter firstly impacts the rock to generate breaking pit and then PDC cogging carries out shearing. And when the PDC-dominated hybrid bit is used, the PDC cogging creates grooves by conducting scraping and then the rolling cutter breaks the rock. Second, the temperature of a hybrid bit rises rapidly in the initial stage of rock breaking, and after a while it tends to be stable and the temperature increases with the increase of the weight on bit (WOB). Third, compared with a PDC bit or a cone bit, a hybrid bit has a lower temperature in the process of rock breaking. The rock-broken volume of the hybrid bit is larger than the sum of a single PDC bit and a single cone bit. Fourth, the rock breaking temperature of a hybrid bit in hard strata is higher than that in soft strata, while the resulted rate of penetration (ROP) is opposite. Fifth, a bit's rock breaking temperature and rock breaking characteristics are related to its own structure. In conclusion, the research results are conducive to the design optimization, popularization and application of hybrid bits.