Safely Exceeding Buckling Loads in Long Horizontal Wells: Case Study in Shale Plays

Abstract

Summary Drilling operations face several limits that intensify uncertainty and risks. Because of the deeper and/or longer wells, drilling equipment is pushed to its mechanical and endurance limits. The general industry perception is that when drillstrings or casing strings exceed conventional helical-buckling criteria, they cannot be operated safely in the hole because the risk of failure or lockup is too high. However, some theoretical, experimental, and field case studies have shown that tubular may be run in the hole even in a buckling state, within safe limits. This paper shows a case study in long horizontal wells for which helical-buckling load has been exceeded without compromising the success of the operations. Drilling data from Bakken field in North Dakota have been gathered, analyzed, and compared with an advanced drillstring-mechanics model that enables simultaneous calculation of torque, drag, and buckling. A strong focus has been placed on the comparison between conventional buckling criteria and drillpipe (DP) or tubular bending stresses. Field results supported by drillstring modeling suggest that the helical-buckling load has been exceeded during operation at some locations along the drillstring during slide drilling and liner running but with bending stresses at an acceptable level. However, in rotary drilling, buckling should be avoided because it will create high vibrations. In this case study, the effect of drillstring dynamics is not considered.