SPECIAL FOCUS: DRILLING REPORT

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

Metallographic examination of a drill pipe reveals that frictional forces produced while rotating drillstring induced sufficient heat to either locally temper the pipe or cause a phase transformation of the drill pipe material.

Samit Gokhale and Sean Ellis, T H Hill Associates, Inc.; Nicholas Reynolds, SPE

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. In addition, the limitations of available methods used to determine the maximum allowable loads that may be applied when packed off with no circulation are presented.

TWO CASES OF HEAT-INDUCED DRILL PIPE TENSILE FAILURE

Case 1 - South Texas onshore. In December 2002, while making a connection at 11,756 ft MD, the wellbore packed off around the 5-in. 19.50-lb G-105 drill pipe. The drillstring was “worked” by applying torque and tension for about 45 min. The drillstring moved up the hole with a loss of 60 kips as noted by rig personnel. The drillstring was pulled and a fractured joint of the 5-in. 19.50-lb G-105 drill pipe was found at 9,553 ft.