Study Explores Mechanisms of Surface Damage on Coiled Tubing

Although several kinds of mechanical damage cause coiled tubing (CT) failure, longitudinal plowing marks (LPMs) account for a large portion of such damage. Understanding the mechanisms of LPM damage on CT surfaces will help reduce the occurrence of this type of damage. In this paper, the authors study the stress status of CT string held by gripper blocks, the axial force distribution of gripper blocks, and the longitudinal resonance of CT strings in vertical wells.

Introduction

The overwhelming majority (greater than 80%) of CT failures have been classified into four categories: corrosion, mechanical damage, string-manufacturing issues, and human error. Of these, failures caused by mechanical damage constitute almost 30% of all CT failures.