Drillstring Rotation Control for Stick-Slip and Wave Energy Reduction
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Solution Overview
Problem
Existing drilling technologies face challenges in controlling rotational vibrations and stick-slip phenomena during oil and gas well drilling, which can lead to reduced drilling rates, bit wear, and torsional damage, and previous methods often compromise optimal drilling parameters to mitigate these issues.
Innovation Solution
A method and controller that optimize the rotation speed of the drillstring by reconciling conflicting objectives of maintaining a stable rotation speed and minimizing downgoing rotational energy, using an expression that adapts to changes in resonant frequency without requiring accurate modeling of the drilling system, and can be implemented as an outer controller with existing drive systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active methods are used to dampen oscillations and prevent stick-slip by adjusting drilling speed and weight on bit, then stick-slip is reduced, but optimal drilling parameters cannot be maintained
Solution Approach 1:
The system continuously measures the actual rotation speed of the drillstring and compares it with the desired rotation speed, using this feedback to calculate and adjust the downgoing energy component in real-time, enabling dynamic prevention of stick-slip while maintaining optimal drilling parameters
Solution Approach 2:
The patent replaces traditional mechanical damping methods (which physically reduce oscillations) with a control system that uses energy calculation and modulation to prevent stick-slip, allowing optimal mechanical drilling parameters to be maintained while still preventing harmful vibrations
2Productivity
If drilling speed is increased to improve rate of penetration, then productivity increases, but rotational vibrations and stick-slip are exacerbated
Solution Approach 1:
The system calculates the downgoing energy component before it can cause harmful vibrations, and takes preliminary action by modulating the drive system to prevent the buildup of excessive rotational energy that would lead to stick-slip and harmful vibrations
Solution Approach 2:
The system dynamically adjusts the rotation speed around the optimal value based on real-time energy calculations, allowing the drilling speed to vary within acceptable ranges to maintain both high productivity and low vibrations, rather than using fixed conservative speed limits
3Measurement precision
If accurate modeling of the drilling system is used to control rotational vibrations, then control precision improves, but system complexity increases
Solution Approach 1:
The patent extracts only the essential downgoing energy component from the complex drillstring dynamics using a simplified calculation based on measured rotation speed and desired rotation speed, avoiding the need for comprehensive system modeling while achieving effective control
Solution Approach 2:
The system uses the calculated downgoing energy component as an intermediary parameter that bridges the gap between simple measurements and effective control, enabling precise vibration control without requiring direct complex modeling of the entire drilling system
Data Source
AI summary
An apparatus and method for controlling a drilling system in a manner that reduces stick-slip by receiving a desired rotation speed v0 of the drive system to rotate the drillstring, receiving property measurements of the drilling system, and deriving therefrom a rotation speed vup of upgoing rotational waves of the drillstring associated with upgoing rotational energy in the drillstring. An actual rotation speed v of the drive system to rotate the drillstring is determined by representing energy in the drillstring as a mathematical expression containing a sum of rotational energy produced by the drive system and downgoing rotational energy caused by the upgoing rotational waves that are reflected downwardly at an upper end of the drillstring, and then optimizing the mathematical expression, which is then used for controlling the drive system to rotate the drillstring at v.