Experimental and computational failure analysis of drillstrings

Drillstring failure analysis in an Iranian oilfield is investigated in this paper. A database containing over 750 failures developed and some conclusions were made. Based on the gathered database, the effects of the depth and casing pipe installation points were examined. The failures were investigated by metallurgical examinations and computational approach using finite element method. The results show that the fatigue cracks produced by different type of drillstring vibrations were responsible for majority of failures. Moreover, dynamic post failure analyses were done to predict the critical rotary speeds and the response of drillstring components. The results have been found to agree well with the field experiences.