Discussion on the Reason of 158.8mm Drill Collar Breaking in Hole in Chengbei 303 Well

By checking 158.8mm drill collar breaking in 311.2mm,215.9mm well bore many times and the appearance of fish breakpoint in Chengbei 303 well, analyzing drill tool structure and the calculation of drill collar bending strength ratio, the reason of drill collar breaking in hole is discussed. And the paper puts forward the problem of drill tool defecting detection, which will be avoided in the future similar situation.