Drillstring failure analysis and its prevention in northeast Sichuan, China

In this paper, the causes for drillstring failure encountered during drilling practice in northeast Sichuan region (China) are systematically investigated based on more than 130 failure cases. The fault tree of drillstring failure in northeast Sichuan (China) is then constructed with considering the drillstring failure as the top event of the fault tree. The minimal cut sets and the minimal path sets of the fault tree are respectively calculated using Boolean algebra based on the fault tree structure. The calculated probability of drillstring failure through FTA method is compared against the statistical value. There exists a good agreement between the calculated and statistical probability. In addition, three importance indexes of basic events in the fault tree, including structure importance index, probability importance index and criticality importance index, are computed. According to the calculated three importance indexes, countermeasures for preventing drillstring failure have been proposed from five perspectives so as to reduce the incidence of drillstring failure in northeast Sichuan (China).