Drill String Vibration: How to Identify and Suppress
Authors: Sotomayor Gabriel P.G. , Placido Joao Carlos , Cunha J.C. 
Published: December 2007

Drill string vibrations can diminish the life of the pipe by accelerating the process of fatigue. Also excessive vibration can cause pipe failure, wash-outs and decrease in the penetration rate. This work describes the first experience in Brazil on identification and suppression of vibrations of the pipe string during drilling operations. The article shows field tests with indications of many types of possible vibrations (axial, longitudinal, torsional, stick-slip) obtained from the interpretation of the drilling parameters acquired in high frequency. It is also shown how to suppress these vibrations by modification of the drilling parameters or by using soft-torque rotary system (STRS).

The field experience shown in the paper demonstrates that it is important to measure and suppress (or minimize) the vibrations in order to have better rate of penetration and more safeness in the drilling process regarding drill string failures.

Introduction

Drilling costs can be reduced with the use of technologies that make the drilling process more efficient. Recent some field tests on how to detect and control vibrations were performed in Brazil. One of the advantages of the tool used is its low cost, which is not common among the tools available in the market. Although similar experiences were realized before, the ones described in this article were the first performed in Brazil and are part of a new drill string monitoring system now being implemented.

Brief Description of Possible Drillstring Vibrations Mainly reasons for drill string vibrations are due to the contact of the bit with the formation and the contact of the string (drill pipes, collars, stabilizers) with the well wall. Also other causes like bent pipes and misalignment of the drill string can cause or increase the severity of drill string vibrations. Those vibrations can generate axial, lateral and torsional movements on the bit and the drill string.

Depending on the severity of the problem, vibrations can cause loss of efficiency on the drilling process and conduct to pipe fatigue, reduction of bit life and unexpected changes in the direction of the well.

Axial Vibration. This type of vibration can cause jumps in the drillstring and slow down the rate of penetration. Besides that, the bouncing also can damage the bit and the BFlA (breaking cutters and bearings and leading to fatigue failure). Axial vibration is more common when drilling with roller cone bits. In case of shallow vertical wells the vibration can be noticed at surface with variations in the hook load and bouncing of the kelly or topdrive. At greater depths and/or directional wells the vibration may be dampened and a vibration detection system is needed to identify the problem at surface, although the damage in the bit and BHA will still be the same.

Torsional Vibration. This vibration makes the rotation of the bit to be irregular and may cause damage to the bit and pipe connections reducing the drilling performance. The most common torsional vibration is called "stick-slip". In this case, the bit or stabilizer decreases its rotational speed, due to tight hole for example, while the rotary table or the top drive remains with the same velocity. This process makes the bit or stabilizer to accumulate an increasing amount of energy up to a point when it breaks free with a very high rotational speed. This torsional wave travels in the string from the bottom hole up to the surface and back to the bit and continues in this behavior unless the drilling parameters are changed in order to interrupt it.

Lateral Vibration. This vibration occurs when the bit or the stabilizer rotates with a center of rotation that is not coincident with the center of the well, which will cause hole enlargement.