Mitigate friction of coiled tubing by optimization and axial vibrations to facilitate extended reach drilling operations

A latest development in the drilling industry is the use of coiled tubing for drilling operations (CTD) that has emerged as a viable technique to ensure cost effective and trouble free drilling operations as compared to conventional jointed pipe drilling. The major challenge in CTD is the buckling that initiates as a consequence of it being a long slender tube and friction between the borehole and the tubing is known to be the main cause. This friction causes the CT to buckle sinusoidally and with increasing axial load ultimately to a helical configuration. Sufficient wall contact forces (WCF) are developed at the well bore and tubing interface thus eventually leading to a zero force transfer downhole. Thus a lockup situation is reached, beyond which the drilling cannot proceed further. Vibration is understood to be a well known technique to reduce friction between contacting forces in many engineering systems. This work presents a detailed analysis of factors that have significant influence on wall contact force, friction, lockup depth and hence buckling. A numerical simulation based technique is used to mitigate friction to reduce buckling, by applying axial vibrations. Various frequencies of axial vibrations were applied and their effect on friction and WCF is studied. A significant improvement in lockup depth was recorded while exciting the tube axially.