Marine Vibrator Control System Reducing Harmonics via Iterative Learning
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Solution Overview
Problem
Marine seismic surveying techniques face challenges in reducing environmental impact and harmonics interference, particularly when using marine vibrators, which can lead to correlation noise and interference between multiple vibrators operating at different frequency ranges.
Innovation Solution
The implementation of a control system for marine vibrators that employs an iterative learning control (ILC) mechanism, utilizing both near-field and far-field sensors to generate repeatable signals and reduce harmonics, allowing for the use of arbitrary signals and direct spread spectrum techniques to minimize peak energy and harmonics, thereby reducing environmental impact and improving data quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If marine vibrators use sweep signals to generate seismic energy, then environmental impact is reduced compared to impulsive sources, but harmonics are generated that cause correlation noise and interference between multiple vibrators
Solution Approach 1:
The patent implements a feedback control system where sensors (hydrophones, accelerometers, or GPS-aided position systems) monitor the actual output of the marine vibrator, and the control system adjusts the drive signal in real-time to minimize harmonics. The feedback loop compares the measured vibration signal with the desired sweep signal and generates corrective control signals to eliminate harmonic content, thereby resolving the contradiction between environmental friendliness and harmonics reduction.
Solution Approach 2:
The patent changes the parameters of the drive signal dynamically during the sweep operation. By adjusting amplitude, frequency, and phase parameters in real-time based on feedback measurements, the system optimizes the sweep signal to minimize harmonics while maintaining the environmental benefits of spread-spectrum operation. This parameter optimization allows the vibrator to operate at lower peak amplitudes with reduced harmonic content.
2Productivity
If multiple marine vibrators operate simultaneously at different frequency ranges, then surveying efficiency increases, but harmonics from one vibrator interfere with fundamentals of other vibrators
Solution Approach 1:
The feedback control system monitors not only the individual vibrator's output but also the combined field when multiple vibrators operate simultaneously. The control system adjusts each vibrator's drive signal to account for interactions with other vibrators, ensuring that harmonics from one vibrator do not interfere with the fundamental frequencies of others. This enables multiple vibrators to operate in close proximity without mutual interference.
Solution Approach 2:
The system performs preliminary characterization of each vibrator's harmonic content and transfer function before actual survey operations. Based on this pre-characterization data, the control system pre-calculates optimal drive signals that minimize potential interference between multiple vibrators. This preliminary preparation allows multiple vibrators to be deployed simultaneously with predetermined frequency assignments that avoid harmonic conflicts.
3Reliability
If feedback systems are used to reduce harmonics in marine vibrators, then signal repeatability improves, but certain feedback systems cannot effectively reduce harmonics and may add complexity
Solution Approach 1:
The patent implements a practical feedback control system that balances effectiveness with simplicity. The system uses readily available sensors (hydrophones, accelerometers, or GPS-aided position systems) and standard signal processing techniques to achieve harmonic reduction. The feedback loop is designed to be computationally efficient, using direct correlation methods and simple transfer function calculations that can be implemented in real-time without excessive complexity, while still achieving effective harmonic reduction and signal repeatability.
Solution Approach 2:
The system uses the vibrator's own output signal as the basis for generating corrective feedback, making the system self-regulating. The feedback control uses the measured vibration signal directly to generate the corrective drive signal, eliminating the need for complex external reference systems or sophisticated control algorithms. This self-service approach achieves effective harmonic reduction with minimal added complexity.
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 reduces peak amplitudes by up to 50 dB, minimizes harmonics, and enhances data quality while allowing multiple vibrators to operate simultaneously without interference, thus providing a more environmentally friendly and efficient seismic surveying method.
Implementation Method 1
measuring movement of an outer shell of the marine vibrator using a motion sensor to obtain a motion sensor signal
Implementation Method 2
running an iterative learning control characterization for the marine vibrator on the motion sensor signal
Implementation Method 3
The marine vibrator may then be operated to generate the seismic energy
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Disclosed are control systems for marine vibrators. An example method may comprise recording a signal at a seismic sensor; running an iterative learning control characterization for a marine vibrator on the signal from the seismic sensor; measuring movement of an outer shell of the marine vibrator using a motion sensor to obtain a motion sensor signal; and controlling the marine vibrator using the motion sensor signal as a reference signal.