Failure analysis of drillstring in petroleum industry: A review

• Understanding of a complete separation of bottom hole assembly (BHA) is conducted.
• Effect of vibrations, slip cuts, etc. on initiating cracks and drillstring failures is undertaken.
• The concepts of drilling process and drillstring components in the oilfield are discussed.
• The common failures occurred in drillstring and their main causes are reviewed.
• The effect of several working parameters on life of drilling tools is presented.

Understanding the failure analysis of drillstring and its components i.e., drill collar and drilling bit is one of the essential issues in the oil and gas industry for the high cost of oil well drilling. Different ways such as air drilling, percussion drilling and downhole hydraulic ultra-high pressure (UHP) jet assisted drilling have been often used to improve the rate of penetration (ROP), minimize the cost of drilling per foot and diminish well deviation. Nevertheless, these drilling ways aggravate the working conditions of the downhole drilling tools materials and hence their properties cannot meet the demands of these conditions and consequently causing a risk drillstring failure. The unfavorable geological conditions and the repeated impact for breaking the rock may also cause severe bit bouncing and violent vibration. Tooth loss, tooth fracture, tooth wear and microcracks in addition to drill pipe fatigue from bending stress caused by buckling load are realistic examples of failure modes which occurred in the drilling tools. This study comprehensively describes the reasons causing these failure modes in order to manage risks and achieve high performance of wells and borehole sections. The role of working parameters i.e., bottom hole temperature and solid content on the drilling tools' life time, and the role of predrill predictions of pore pressure or wellbore stability on the drilling process are presented.