Drill String Vibration Damping via Impedance Matching
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Solution Overview
Problem
Existing methods for mitigating stick-slip vibrations in tool strings, such as those used in drilling systems, are limited in effectively damping all frequencies due to frequency-dependent components, leading to incomplete absorption of torsional wave energy and potential for standing waves and resonance.
Innovation Solution
A method and system that adjust the rotational speed of the tool string by calculating a rotation correction signal based on the tool string impedance, matching the drive system's impedance to that of the tool string, and combining this with a control signal to absorb torsional waves across a selected frequency band, ensuring the drive system's inertia appears zero to the waves, thus absorbing energy for all frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing methods for mitigating stick-slip vibrations are used, then some vibration damping is achieved, but frequency-dependent components limit effectiveness across all frequencies
Solution Approach 1:
The patent changes the parameter of drive system impedance by dynamically adjusting the rotational speed based on detected torsional wave characteristics. By modifying the operating speed parameter in response to wave frequency and amplitude, the system adapts to dampen vibrations across different frequencies rather than being limited to a fixed frequency range.
Solution Approach 2:
The system transitions from a static vibration mitigation approach to a dynamic one by continuously monitoring torsional wave parameters and adjusting the drive speed in real-time. This dynamic adjustment allows the drive system to adapt its impedance characteristics to match and absorb waves across a broad frequency spectrum.
2Loss of energy
If the drive system impedance is matched to tool string impedance, then torsional wave energy is absorbed across all frequencies, but control system complexity increases
Solution Approach 1:
The patent implements a feedback control mechanism where torsional wave parameters (amplitude, frequency, direction) are continuously detected and used to adjust the drive system rotational speed. This closed-loop feedback enables automatic impedance matching without requiring complex manual tuning or additional hardware components.
Solution Approach 2:
The rotational speed acts as an intermediary parameter that mediates between the drive system and tool string impedance mismatch. By adjusting this intermediate parameter, the system achieves energy absorption across all frequencies without directly modifying the fundamental impedance characteristics of either the drive system or tool string.
3Stability of the object's composition
If rotational speed is adjusted to absorb torsional waves, then standing waves are prevented, but precise speed control is required
Solution Approach 1:
The system applies periodic adjustments to the rotational speed that correspond to the detected torsional wave frequency. By synchronizing the speed modulation with the wave period, the system effectively counteracts wave formation and prevents standing waves without requiring excessive precision in continuous speed control.
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 all vibrational modes within a selected frequency range, including harmonics, reducing reflection coefficients and preventing standing waves, thereby enhancing the reliability and performance of drilling equipment by minimizing shock loads and wear.
Implementation Method 1
adjust the rotational speed of the tool string by calculating a rotation correction signal based on the tool string impedance, matching the drive system's impedance to that of the tool string
Implementation Method 2
absorb torsional waves across a selected frequency band, ensuring the drive system's inertia appears zero to the waves, thus absorbing energy for all frequencies
Implementation Method 3
damping vibrations in a tool string system
Implementation Method 4
the coefficient of kinetic friction between the parts is less than the coefficient of static friction between the parts
Implementation Method 5
any drive connection in a mechanical system exhibits some degree of compliance, i.e. a tendency to yield or bend under load, within the elastic limit of the material
Data Source
AI summary
The invention provides a control system and method for limiting vibrations in a tool string system, comprising a relatively heavy rotatable device, such as a pump system or a bottom hole assembly, connected to a long rotatable tool string driven by a drive system. The control system comprises feedback of both torque and rotational speed signals to correct the set rotational speed. An objective is to maintain the drive speed over torque ratio equal to the connected tool string impedance. A secondary objective, for lower frequencies, is to approach and maintain a setpoint speed as drive rotation speed. The system may include a rotational speed sensor and a torque sensor, with the latter optionally replaced by a motor torque signal already available from a variable frequency drive (VFD) for an AC motor and the current safeguarding signal for a DC motor.