Coiled Tubing Vibration and 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.

A study of the influence deformation of the drilling riser on the longitudinal oscillations of the drill string

The article deals with the study of the effect of drilling riser transverse vibrations on the longitudinal vibrations of the drill string and the change of the dynamic component of weight on the bit when drilling wells from floating drilling vessel in deep sea conditions. The impact assessment was carried out by comparing the results of the simulation of the drilling system in the software based on the Modelica language. For this purpose, a simulation model has been created to enable the study of the operation of the «drill ship – riser wire tension system – drilling riser – drill string heave compensator – drill string» system in the case of irregular sea agitation obtained from decomposition the JONSWAP energy spectrum. The influence of the deformation of the drilling riser on the axial vibrations of the drill string is taken into account by introducing into the "classical" equation of the axial vibrations of the drill string the nonlinear term of the longitudinal-transverse strain. The drill string transverse deformation was determined based on the assumption that the axes of deformation of the drilling riser and drill string were coincident in the course of operation. A series of simulation experiments was carried out in the case from three to six WMO sea state code, absence of action of sea currents and active mode of work of the drill string heave compensator. The obtained results show that the greatest influence of the deformation of the drilling riser on the axial vibrations of the drill string is observed in the section at the level of the well head, where the amplitude of longitudinal vibrations increases up to 4 times. In general, the deformation of the drilling riser causes the growth of the dynamic impact factor of weight on the drill bit to increase by 4-7% for the investigated structure of the drilling system.