A new type of coiled tubing (CT) failure mechanism has appeared in the past four years. The failures occur in CT strings used for frac plug milling in extended reach horizontal wells. Although significant effort has been put into understanding these failures in the past several years, the mechanism that leads to them is still not well understood. Different hypotheses have been discussed among the industry, like the impact the use of extended reach tools (ERT) have on the low cycle fatigue performance of the CT [1] [2] [3]. The objective of this paper is to further investigate possible causes for these failures focusing on the analysis of the effects of circulating pressure and strain on the mechanical properties of the CT that could eventually contribute to a premature failure.

A new coiled tubing (CT) failure mechanism has appeared in the past two to three years. The failures occur in CT strings used for frac plug milling in extend reach horizontal wells. The objective of this paper is to investigate a possible cause for these failures. The primary emphasis is analyzing the dynamic response of the CT to axial vibrations induced by a downhole extended reach tool [1], and the resulting tubing material response leading to failure.