October 2007
Special Focus

Rotating while packed off may cause unexpected heat-induced drill pipe tensile failures

The amount of tensile pull that can be applied to free a stuck drillstring is usually restricted by the drillstring’s minimum Margin Of Overpull (MOP).1 To free a stuck string, the drillstring is often rotated and pulled simultaneously. When this is done, the maximum permitted pull is reduced, depending on the amount of torque applied. Application of pull, either based on MOP or the decreased tensile rating given the applied torque, has resulted in instances of overload failures of drill pipe. These failures have occurred at loads significantly lower than the drillstrings rated capacity. As the material gets locally heated, the material hardness decreases. The actual load capacity of the drillstring depends on the temperatures reached downhole. This paper discusses the factors that contribute to these failures and provides test data to support the findings.

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