Lateral vibration: the key to BHA failure analysis

Axial and torsional vibration analysis of three bottomhole assemblies was unable to identify the cause of repeated washouts and twistoffs. Finite element analysis, involving the six degrees of freedom available to the BHA and taking into account wellbore trajectory, WOB and other variables, established lateral vibrations as the probable culprit. Failures occurred when operating at speeds and in the drillstring locations predicted.