Abstract: Rock drillability evaluation is an important basis for opitimizing drilling acceleration tools and parameters. A scientific and reasonable assessment of rock drillability is vital to drilling engineering. Drillability testing and classification methods need continuous improvement to keep pace with the development of drilling technology,and their scientific validity requires repeated verification. Thus,experiments were conducted on various rock samples with different strengths and lithologies. The rationality,repeatability,and universality of the rock drillability index testing and classification methods were explored by comparing with the foreign SJ drillability testing and corresponding methods. The research results show that:(1)Under a drilling pressure of 1.0 kN,the improved PDC micro drill bit can effectively solve the slipping problem in hard formations. The improved roller cone micro drill bit,operating at a rotational speed of 90 r/min,has effectively addressed the issues of restricted cone-tooth rotation and excessive tooth wear. (2)For hard formation rocks,the drillability testing methods for PDC and roller cone micro drill bits demonstrate better repeatability compared to the SJ drillability testing method. (3)The improved PDC and roller cone drillability testing methods significantly reduce the proportion of invalid test results,better adapting to current advances in drilling technology. (4)The drillability classification method facilitates the differentiation of rock drilling difficulty,while also establishing an extensible framework for future evaluation of drillability in harder rocks under bottom-hole pressure conditions.

Key words: drilling engineering, rock, drillability, PDC bit, cone bit

摘要： 岩石可钻性评价是钻井提速工具和参数优选的重要依据,科学合理地评价岩石可钻性对钻井工程至关重要。岩石可钻性测试及分级方法需不断改进以适应钻井技术的不断发展,同时需要反复验证其科学性。为此,尽可能多选用覆盖不同强度和岩性的岩样进行实验,并对照国外SJ可钻性测试及分级方法,讨论岩石可钻性指数测试和分级方法的合理性、可重复性、普适性。研究结果表明:①改进的PDC微钻头结构采用钻压1.0 kN,较好地解决了硬地层打滑现象,改进的牙轮微钻头结构使用转速90 r/min,较好地解决了牙轮齿不能自由旋转以及牙轮齿磨损过快的问题;②对于硬地层岩石,PDC和牙轮微钻头可钻性测试方法较SJ可钻性测试方法可重复性更好;③改进的PDC和牙轮可钻性测试方法能显著地降低无效测试结果的比例,更适应当前钻井技术的进步;④可钻性分级方法能够更易区分岩石的难钻程度,同时又为钻遇更坚硬岩石及考虑井底压力下的可钻性评价留足了空间。

关键词: 钻井工程, 岩石, 可钻性, PDC钻头, 牙轮钻头