A Field Method for Controlling Drillstring Torsional Vibrations

Abstract

Torsional vibrations are detrimental to the life of drillstring components (1,2,3,4). Although methods of controlling them have been proposed (1,3,4), their general dependence on strain gauges to measure drillstring torque make them unsuitable for the drilling environment. In this paper we describe a new, practical, system which does not use such a sensor, and present extensive field test results taken from a semisubmersible rig drilling in the North Sea. The system was shown to be very effective in suppressing torsional vibrations. It uses measurements of motor current, acceleration and a microprocessor to modulate the drive to the motor.An analysis is given to show that not only does the system performs just as well as one using a strain gauges sensor, but it also performs better than a system which uses motor current only. Considerations for the system design are also discussed.A significant reduction of drillstring torsional vibrations, DTV's, will reduce the cost of drilling wells by reducing damage to drillstring components and lost rig time. Drilling efficiency is enhanced through the suppression of "stick-slip" motion at the bit.References and illustrations at end of paper.

Sliding-mode control of a multi-DOF oilwell drillstring with stick-slip oscillations

“…For the control problem, there are also several solutions. For example, [4], [7], [10] proposed a vibration absorber at the top of the drillstring (referred to as soft torque rotary system). A classical PID control structure at the surface is used in [6], [11], [12].…”

D-OSKIL: A New Mechanism for Controlling Stick-Slip Oscillations in Oil Well Drillstrings

“…Historically, the experience of drillers has revealed that the manipulation of different drilling parameters (increasing the rotary speed, decreasing the weight-on-bit (W oB), modifying the drilling mud characteristics, introducing an additional friction at the bit [25], etc) is an effective strategy to suppress stick-slip motion [28]. However, this strategy depends too much on the personal skills of each drilling technician to be really effective.…”

Practical approach to modelling and controlling stick-slip oscillations in oilwell drillstrings

“…Manipulating different drilling parameters as increasing the rotary speed, decreasing the weight-on-bit (WOB) or modifying the drilling mud characteristics are shown in the field to suppress stick-slip motion [25]. More effective control methodologies have appeared in the literature in order to compensate drillstring stick-slip vibrations.…”

“…These methods can be divided into classical control techniques and more sophisticated ones. In the first group, the following ones are highlighted: 1) Introduction of what is regarded as soft torque rotary system (STRS) at the top of the drillstring [7], [25], [26]. A torque feedback is proposed, the underlying idea is making the top rotary system behave in a "soft" manner rather than as a fixed heavy flywheel.…”

“…This system has been incorporating in different wells and it has reduced significantly torque fluctuations at the surface (up to 80%) and bit stick-slip conditions [10], [31]. 2) Introduction of a vibration absorber at the top of the drillstring [9] which follows the same approach given in [7], [25]. 3) Introduction of a PID controller at the surface in order to control the rotary speed [21].…”