Abstract: Coiled Tubing (CT) is the "neural line" of the "universal working machine". The safe operation of CT is related to the entire construction process. The service life of CT is one of the important indicators of the safe operation. At present, there is little study on the safety assessment of the whole life of CT operation. Survival analysis was used to study 6 influencing factors of CT and 20 component variables. The Kaplan-Meier analysis method was used to describe the single-factor survival time of CT fatigue life, and the Cox proportional hazard model was used to perform multi-factor analysis in combination with the effective time of CT service. The comparison between the cumulative fatigue results and the Cox proportional hazard model calculation results shows that the model is feasible. The research results show that collinearity test and PH hypothesis are feasible for 399 samples survival analysis; among the classification variables:OD, wall thickness, corrosion, and welding have significant effects on the risk of CT; the risk rate of large-diameter CT (diameter>50.80 mm) is 1.484 times that of smalldiameter CT (diameter<50.80mm); the corrosion risk rate of H₂S environment is 2.509 times that of no corrosion risk rate; The risk rate of straight welds is 5.595 times that of no welds; the conclusions of the study are consistent with the statistical results of field CT failure. The four-level evaluation criteria proposed based on the cumulative survival rate and field failure statistical results have guiding significance for the safe operation of the CT in drilling, completion and gas lift.

Key words: survival analysis, Coiled Tubing, Kaplan-Meier method, Cox proportional hazards model, level 4 evaluation