Stick-Slip Vibration Suppression in Drill String Using Observer-Based LQG Controller

Area of Science:

• Engineering
• Control Systems
• Petroleum Engineering

Background:

• Rotary drilling systems are crucial for hydrocarbon exploration and production.
• Drill string vibrations, particularly torsional stick-slip, reduce efficiency and increase costs.
• Existing methods struggle to effectively mitigate these severe vibrations.

Purpose of the Study:

• To eliminate severe stick-slip vibrations in rotary drilling systems using an LQG observer-based controller.
• To address nonlinear rock-bit interactions and unmeasurable bit rotational velocity.
• To enhance the stability and efficiency of hydrocarbon exploration and production operations.

Main Methods:

• Designed an LQG (Linear Quadratic Gaussian) observer to estimate unknown model inputs based on surface measurements.
• Implemented the observer-based controller in a 10-degree-of-freedom drill string model.
• Validated performance through simulations in SimScape/Matlab and compared with other control strategies.

Main Results:

• The proposed LQG observer-based controller effectively suppressed severe stick-slip vibrations.
• Demonstrated good robustness against various simulation scenarios and structured disturbances.
• Outperformed other controllers, including H∞, in terms of performance and sensitivity.

Conclusions:

• The LQG observer-based controller is a highly effective solution for mitigating stick-slip vibrations in rotary drilling.
• The approach offers improved drilling efficiency and reduced operational expenses.
• Recommended for implementation in smart rotary drilling systems for enhanced performance.