Rotary Steerable Pad Control for Drill String Oscillation Mitigation
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Solution Overview
Problem
Existing methods struggle to effectively mitigate torsional drill string oscillations, particularly backward whirl and harmonic stick slip, which can cause severe component fatigue and catastrophic failure during downhole drilling operations.
Innovation Solution
A rotary steerable system with at least three pads is used to measure stick slip and whirl amplitudes, comparing them to thresholds, and simultaneously actuating the pads to mitigate or promote oscillations when thresholds are exceeded, employing a roll-stabilized control unit for precise pad control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional drill string components and drilling parameters are used, then drilling operations can proceed, but torsional oscillations (backward whirl and harmonic stick slip) cause severe component fatigue and catastrophic failure
Solution Approach 1:
The patent applies inversion by promoting fundamental stick slip oscillations (typically considered harmful) to counteract and mitigate the more damaging backward whirl and harmonic stick slip oscillations. The RSS pads are actuated to enhance fundamental stick slip, which then interferes destructively with the harmful higher-frequency oscillations, reducing overall vibration damage to drill string components.
Solution Approach 2:
The system dynamically changes operational parameters by adjusting RSS pad actuation forces and timing based on real-time detection of oscillation amplitudes and frequencies. The controller modulates pad engagement to shift the system's torsional response characteristics, transforming the drill string's vibrational behavior from a harmful state to a less harmful state.
2Object-affected harmful factors
If intensive mitigation efforts are applied to reduce damaging oscillations, then some oscillation tendency is reduced, but backward whirl and harmonic stick slip remain challenging problems
Solution Approach 1:
The system employs self-service by using the drill string's own fundamental stick slip oscillations as a mitigation mechanism. Rather than introducing entirely external counter-vibrations, the system harnesses and amplifies the naturally occurring fundamental frequency oscillations through RSS pad actuation, allowing the system to self-regulate and mitigate harmful oscillations using its inherent vibrational characteristics.
Solution Approach 2:
The patent implements feedback control by continuously monitoring drill string oscillations with sensors, analyzing the amplitude and frequency characteristics, and dynamically adjusting RSS pad actuation in response. The controller uses real-time feedback on stick slip and backward whirl amplitudes to modulate pad forces, creating a closed-loop system that adapts to changing drilling conditions and oscillation patterns.
3Object-affected harmful factors
If RSS pads are actuated to mitigate stick slip oscillations, then stick slip is reduced, but this may not effectively address harmonic stick slip and backward whirl
Solution Approach 1:
The patent applies universality by designing the RSS pad actuation system to perform multiple oscillation mitigation functions simultaneously. The same pad actuation mechanism that reduces fundamental stick slip is also configured to mitigate harmonic stick slip and backward whirl through coordinated multi-frequency actuation patterns. The system universally addresses multiple types of torsional oscillations using a single integrated control approach rather than separate specialized systems for each oscillation type.
Data Source
AI summary
Wellbore operations include rotating a drill string in a wellbore. The drill string includes a rotary steerable system having at least three pads configured to contact the wellbore wall to steer a direction of drilling. These are simultaneously actuated while rotating the drill string to mitigate stick slip, harmonic stick slip, or backward whirl oscillations.