Drill String Stick-Slip Mitigation via Impedance Matching
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Solution Overview
Problem
Stick-slip oscillations during drilling operations cause fatigue failures, excessive bit wear, and poor drilling rates due to nonlinear downhole friction and torsional vibrations in drill strings.
Innovation Solution
A system and method combining torque feedback and impedance matching using a feed-forward speed controller to mitigate stick-slip oscillations by adjusting the drive system's speed and stiffness, allowing for effective dampening of torsional waves without impairing the drilling rate of penetration (ROP).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the surface drive system runs at constant speed, then the drive system acts as an effective reflector and maintains stable operation, but torsional vibrations build up and severe stick-slip oscillations occur
Solution Approach 1:
The patent applies dynamics by transitioning from constant speed control to variable speed control. The drive system dynamically adjusts its rotational speed in real-time to counteract stick-slip oscillations, making the system adaptive rather than static. This allows the drive system to absorb and dissipate torsional vibrations rather than reflecting them, resolving the contradiction between stability and vibration mitigation.
Solution Approach 2:
The patent implements feedback control by continuously monitoring downhole torque and surface torque fluctuations, then using this information to adjust the drive system speed. The feedback mechanism detects oscillation patterns and automatically modifies operational parameters to reduce stick-slip, transforming the drive system from a passive reflector to an active vibration suppressor.
2Object-affected harmful factors
If impedance matching is used to dampen torsional waves, then stick-slip oscillations are reduced, but the drilling rate of penetration may be impaired
Solution Approach 1:
The patent uses dynamic speed adjustment to achieve impedance matching transiently rather than maintaining fixed impedance conditions. By varying speed in real-time based on oscillation detection, the system can dampen torsional waves during stick-slip events while maintaining optimal drilling speed during normal operation, thus preserving drilling rate while reducing vibrations.
Solution Approach 2:
The patent changes operational parameters (rotational speed) dynamically to achieve impedance matching only when needed for vibration suppression. This selective parameter modification allows the system to maintain high drilling rates during stable conditions while temporarily adjusting speed to dampen oscillations during stick-slip events, resolving the productivity-vibration contradiction.
3Object-affected harmful factors
If torque feedback control is applied to mitigate stick-slip, then oscillations are reduced, but the system complexity increases
Solution Approach 1:
The patent implements torque feedback control by monitoring downhole torque measurements and using this feedback to adjust drive system speed. The feedback mechanism processes torque data to detect stick-slip oscillations and automatically modifies operational parameters, providing vibration mitigation through a relatively simple feedback loop that leverages existing torque measurement capabilities.
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
The solution provides a balanced drive system that effectively dampens stick-slip oscillations while maintaining a high drilling rate, reducing fatigue and wear, and improving drilling efficiency.
Implementation Method 1
A system and method combining torque feedback and impedance matching using a feed-forward speed controller to mitigate stick-slip oscillations by adjusting the drive system's speed and stiffness
Implementation Method 2
Stick-slip may be generally defined as the torsional vibration of downhole components or equipment (e.g., drill pipe, drill bit), as it slides against the edges of the borehole
Implementation Method 3
The oscillations are driven by nonlinear downhole friction
Data Source
AI summary
The present disclosure is directed to systems and methods for rotating a drill string to mitigate stick-slip oscillations. An embodiment includes a method of rotating a drill string driven by a drive system using a control system. The method includes measuring torque values of the drive system with a torque sensor. The method also includes determining a frequency of stick-slip oscillations at the drive system based on the torque values using the control system. The method also includes determining an estimated instantaneous rotational speed of the drive system with the control system based on at least the frequency of stick-slip oscillations and a characteristic impedance of the drill string. The method also includes adjusting the estimated instantaneous rotational speed based on changes in the torque values to define an adjusted estimated instantaneous rotation speed with the control system. The method also includes providing an output signal representing the adjusted estimated instantaneous rotational speed to the drive system. The method also includes controlling rotation of a quill of the drive system based on the output signal.