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石油钻柱主要由方钻杆、钻杆、钻铤三大部分组成，因服役条件十分恶劣，使其成为钻井设备工具中的一个薄弱环节。特别是在深井、超深井及复杂地质环境条件下钻井，钻具失效事故时有发生，四川川东地区仅１９９６年～１９９７年间就发生了人钻具井下断裂事故，造成了很大经济损失。防止和减少钻具失效，关键在预防，为此，根据钻柱各部分在井内的受力特点不同将其划分为钻柱井口处、零应力点上部、零应力点附近、零应力点下部四个钻具

ANALYSIS OF THE CAUSE FOR DRILL STRING FAILURE ACCIDENTS AND THE COUN TERMEASURES

??The drill string for oil well drilling is composed of three major parts,namely,square kelly,drill pipe and drill collar.Very adverse service condition makes the drill string become a weak link in drilling tools.Especially,in case of drilling deep or ultradeep well,or under complex geological conditions,the drill string failure accidents occur sometimes.In East Sichuan region,for example,303 downhole drilling pipe breaking accidents have occurred only during 1996??1997,causing a great pecuniary loss.The key to prevention and reduction of the drill string failure lies in prevention.For this reason,in view of the different stressed characteristics of the different sections of the drill string in borehole,the research is conducted by dividing the drill string into four failure sections,namely,the section at the wellhead and the sections at the upper part,vicinity and lower part of the zero stress point,to investigate the essence and basic reason of the failure,and to put forward scientific and feasible preventing measures,thus,being advantageous to complete and systematic prevention and forecast of the drill string failure.Through analyzing the stressed state of each part of the drill string in borehole,the four main characteristics and basic reasons of the drill string failure that often occurs and is of general character are analyzed and the feasible,scientific and effective measures for preventing these common drill string failure accidents are emphatically proposed in this paper.