PDC钻头破岩效率及稳定性室内试验研究

Laboratory Experimental Study on Rock Breaking Efficiency and Stability of PDC Bit

为评价新研制的PDC钻头在目标岩性地层中的破岩效率与稳定性,以指导钻头优化改进和高效使用,对新研制深层高研磨地层PDC钻头A、页岩气水平段地层专打PDC钻头B在硬砂岩、灰岩、软砂岩及页岩等4种目标地层岩心中开展了全尺寸室内破岩试验。研究结果表明:钻头破岩机械钻速由钻头机械比能与破岩效率共同决定,提高钻压机械钻速升高并不一定意味着破岩效率升高,这取决于使用钻压与最大破岩效率"门限钻压"相对位置,而"门限钻压"受所钻地层岩性及使用钻头影响;钻头破岩稳定性主要取决于钻头振动强度,钻压、转速及地层岩性能够通过切削深度影响钻头振动强度;相同钻压和转速下,钻头A在硬砂岩中破岩效果与破岩稳定性优于灰岩,钻头B在软砂岩中破岩效果与破岩稳定性优于页岩。根据钻头三轴振动强度随切削深度的变化规律,从防止钻头先期损坏、保障2只钻头在4种岩性中机械钻速、工作时间及进尺长度的角度提出了建议。所得结论可为2只钻头结构优化及钻井参数优选提供指导。

In order to evaluate the rock breaking efficiency and stability of the newly developed PDC bit in the target lithologic formation,and guide the optimization,improvement and efficient use of the newly developed PDC bit,full scale laboratory rock breaking tests were carried out on newly developed PDC bit A for deep and high grinding formation and PDC bit B for shale gas horizontal section in four target formation cores,namely,hard sandstone,limestone,soft sandstone and shale.The results show that:the ROP of bit is determined by the specific energy of bit and rock breaking efficiency.The increase of ROP does not necessarily mean the increase of rock breaking efficiency,which depends on the relative position of WOB and the maximum rock breaking efficiency"threshold WOB",while the"threshold WOB"is affected by the lithology of the formation drilled and the bit used.The rock breaking stability of bit mainly depends on the vibration strength of the bit.The drilling pressure,rotation speed and formation lithology can affect the vibration strength of the bit through the cutting depth.Under the same WOB and rotation speed,the rock breaking effect and rock breaking stability of bit A in hard sandstone are better than those in limestone,and the rock breaking effect and rock breaking stability of bit B in soft sandstone are better than those in shale.According to the variation law of the triaxial vibration strength of the bit with the cutting depth,some suggestions are put forward from the aspects of preventing the bit from being damaged in advance and ensuring the ROP,working time and footage length of two bits in four kinds of lithology,which can provide guidance for the optimization and improvement of the structure of two bits and the optimization of drilling parameters.