PDC钻头岩石可钻性测定与分级新方法研究

A New Method for Measuring and Grading of PDC Bit Rock Drillability

PDC钻头作为最重要的油气钻井破岩工具,其岩石可钻性级值是进行钻头个性化设计与选型、优化钻井参数的关键依据,在中硬以上的地层价值尤为重要。然而,我国2000年颁布实施的石油天然气行业标准《岩石可钻性测定及分级方法》却存在明显的缺陷,对中硬以上的岩石经常出现测试无效、无法获得可钻性级值数据的现象。通过对不同岩性岩石试样的大量微钻头可钻性实验测试,发现标准钻压过低、PDC微钻头结构参数不合理是中硬以上岩石测试无效的主要原因。针对这些问题,首先,研究了微钻头切削齿安装角度对其干涉状态的影响规律,提出了最优的微钻头侧转角,消除了微钻头切削齿与岩石发生干涉的可能性;其次,开展了5种岩石在不同钻压下的微钻头钻岩实验,实验数据表明变压可钻性级值与钻压之间呈线性关系,提出了采用钻压分档测试、当量转化分级或分档独立分级的可钻性测试与分级新方法。该方法既能有效解决中硬以上岩石的可钻性测试问题,又能与过去的软岩测试数据相兼容。主要研究成果已经被2016版行业标准《岩石可钻性测定及分级》所采纳。

PDC bit is regarded as the most important rock-breaking tool for oil and gas drilling, the value of rock drillability is the key basis for personalized design, selection and optimization drilling parameters of the drill bit, especially in moderately hard or abrasive formation. However, oil and gas industry standard in China named "Rock drillability measurement and its classification" has obvious flaws on a moderately hard or abrasive rock, problems like invalid test, unable to obtain the drillability evaluation data appear frequently. According to a large number of micro bit test carried on different lithology rock samples, low standard weight on bit and unreasonable side rake angle parameter of micro P D C bit are identified to be the main reasons which lead to invalid test on the moderately hard or abrasive rock. To solve these problems, first, side rake angle of micro bit was modified to eliminate possible interference between cutter and rock on micro bit;secondly, drilling experiments of micro bit with five kinds of rocks under different drilling pressures were carried out before combining the experimental results and the cutting theory together to understand the relationship between drilling pressure and times, put forward drillability measurement and new classification of drilling pressure grading test and equivalent transformation grading. This method can not only solve the moderately hard or abrasive rock drillability test problems effectively, but also be compatible with the old test data of soft rock. The main research results have been adopted by the 2016 edition of the industry standard “Rock Drillability Determination and Classification”.