Fracture Cause of Centralizer Joint of a Well in Drilling and Mining Operation

In drilling and mining operation of a well in the west of the South China Sea, a centralizer broke at the internal thread of joint. The fracture reason was analyzed by macroscopic examination, chemical composition analysis, microscopic morphology analysis, mechanical property test and finite element simulation. The results show that the fracture mode of the centralizer joint was fatigue fracture, and the fatigue crack originated from the thread root of the joint. The decrease of centralizer body outer diameter, and the increasing stress at the joint thread root were the main reasons for the failure of the centralizer. It was suggested that the combination of bottom drill tools should be optimized, and the combination of centralizer, drill collar and centralizer could effectively avoid the relatively great stress concentration at the threaded connection of centralizer.