Failure analysis of a bottom hole motor attached to a coiled tubing

Abstract

During well operations in Mexico, a weight loss incident occurred, accompanied by the detachment of a section of the Bottom Hole Motor (BHM) connected to coiled wellbore tubing. To investigate the cause of the BHM rupture, a comprehensive analysis was conducted, including chemical analysis, metallurgical examination, thickness measurements, hardness, tension, and impact tests, as well as Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS). The results indicated brittle failure, potentially initiated by excessive torque, with evidence of plastic deformation and fatigue. The failure was attributed to weight forces overcoming well-related resistances, generating flexion stresses in the BHM body. Mechanical damages, including scratch marks, and localized deformation areas, indicated that the material is brittle, which is observed in the low elongation values (6 %) and energy impact exhibited. Microscopic analysis revealed predominantly brittle characteristics of the surface fracture. The failure of the BHM occur during attempts to unclog CT due to the material exhibiting low elongation and impact energy, suggesting that the material experienced deformation hardening, and fatigue before reaching failure. Additionally, scratches and excessive torque contributed to the material failing prematurely.