Fabrication of Experimental Setup for Investigation of Drill String Fatigue Failure

Abstract

Drill string and downhole tool failure usually results from failing to control one or more of the vibration mechanisms. The solution starts with the ability to measure different modes and hence identify the different vibration mechanisms. An in house experimental setup was developed to imitate the downhole axial, lateral and torsional vibration modes and mechanisms. Single and coupled vibration modes and mechanisms were created. This paper mainly focused the design and fabrication of the experimental setup. Capability of the setup for creating different vibration modes were examined. Experiments were performed to investigate the effects of rotational speeds and lateral vibration mode on the fatigue life of drill strings. Fatigue life is measured from the number of cycles associated with the amplitude of the stress cycles created due to lateral vibration Results showed that drill string size and lateral vibration stress cycles have significant effects on the fatigue life of the drill string. Investigations also showed that operating on a rotation speed higher than 90% of the drill string critical speed leads to yielding of the drill string. Such setup is essential for oil/gas industries as it can be utilized to investigate and provide solutions for very common problems such as drill string fatigue failure.