Top Drive Torque Control for Drill String Torsional Waves
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Solution Overview
Problem
Drilling operations face challenges with stick-slip phenomena, leading to excessive bit wear, premature tool failures, and poor drilling rates due to torsional vibrations and friction between the drill bit and the formation, which existing control systems fail to effectively mitigate.
Innovation Solution
A control system that regulates the torque output of the drill string drive system based on rotation measurements at the surface, minimizing the reflection of torsional vibrations by using a proportional-derivative (PD) controller to absorb torsional vibrations at the junction between the drill string and the top drive, ensuring no wave is reflected back into the drill string.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional control system is used to regulate drill string rotation, then the drill bit can rotate at high angular velocity, but torsional vibrations and stick-slip phenomena occur causing excessive bit wear and tool failures
Solution Approach 1:
The control system continuously measures the rotational speed of the drill string at the surface and uses this feedback to regulate the torque output of the drive system. The measured rotational speed serves as feedback to adjust the drive torque, enabling active control of torsional vibrations and mitigation of stick-slip phenomena through real-time monitoring and adjustment.
2Productivity
If the drill string is rotated at high speed to maintain drilling rate, then productivity increases, but axial and lateral accelerations and forces increase causing vibrations
Solution Approach 1:
The control system measures rotational speed at the surface and uses this feedback to actively regulate drive torque, damping torsional vibrations that would otherwise amplify axial and lateral accelerations during high-speed drilling operations.
Solution Approach 2:
The system actively controls and dampens torsional vibrations in the drill string through regulated torque output. By controlling the vibrational characteristics of the drill string, the system reduces harmful axial and lateral accelerations that occur during high-speed rotation while maintaining productivity.
3Force
If torque is increased to overcome friction and maintain drill bit rotation, then drilling continues, but stick-slip oscillations are exacerbated causing bit wear
Solution Approach 1:
The control system uses real-time measurement of drill string rotational speed as feedback to dynamically regulate torque output. This feedback mechanism enables the system to apply torque smoothly and prevent the build-up that leads to stick-slip oscillations, thereby reducing bit wear while maintaining drilling progress.
Solution Approach 2:
The control system dynamically adjusts torque output based on measured rotational speed variations. By making torque dynamic rather than constant, the system adapts to changing drilling conditions and prevents the cyclic stick-slip behavior that causes bit wear.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively dampens torsional vibrations, reducing adverse effects of stick-slip, maintaining consistent rotational speeds, and minimizing drill string oscillations, thereby enhancing drilling efficiency and reducing wear on drill components.
Implementation Method 1
the drill string can also exhibit a complicated dynamic behavior resulting in one or more of axial, lateral and torsional vibrations
Implementation Method 2
the drill bit can periodically stop rotating while the top drive continues to rotate the drill string and, thereby, build up torque in the drill string. At one point, the torque overcomes the friction and the drill bit suddenly rotates again
Implementation Method 3
due to torsional vibration and friction between the drill bit and the formation, the drill bit can periodically stop rotating
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A method includes generating a torsional wave that propagates in a drill string having a drill bit coupled at a first end of the drill string and a top drive coupled at a second end of the drill string, and determining first and second components of the torsional wave. The first component propagates from the drill bit to the top drive and the second component propagates from the top drive to the drill bit. The method further includes calculating a first control signal to mitigate the first component, calculating a second control signal to regulate the second component, and generating a torque command based on the first and second control signals to control the top drive to dampen the torsional wave.