Distributed Acoustic Sensing Low Pulse Repetition Rates
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Solution Overview
Problem
Current distributed acoustic sensing (DAS) systems face challenges in efficiently processing low frequency components to accurately determine acoustic levels, especially in downhole exploration and production efforts, where data volume and aliasing issues arise when monitoring over long distances.
Innovation Solution
The DAS system employs low pulse repetition rates and uses a swept-wavelength laser to process the low frequency component of the DAS signal, allowing for reduced data volume and minimizing aliasing, enabling accurate acoustic level monitoring over extended distances by separating temperature and acoustic components through non-linear frequency mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high pulse repetition rates are used in DAS systems, then data acquisition completeness is improved, but data volume increases and aliasing occurs
Solution Approach 1:
The patent applies periodic action by using low pulse repetition rates (e.g., 10 Hz or lower) instead of high repetition rates, creating a periodic sampling pattern that reduces data volume while maintaining adequate coverage for acoustic monitoring over long distances. This periodic approach with extended intervals between pulses directly addresses the contradiction by reducing the quantity of data acquired while preserving essential measurement information.
2Reliability
If high pulse repetition rates are used in DAS systems, then data acquisition completeness is improved, but aliasing occurs
Solution Approach 1:
By implementing periodic action with low pulse repetition rates, the system avoids the harmful aliasing effect that occurs with high repetition rates. The extended periodic intervals allow the system to capture acoustic information without the frequency folding and distortion characteristic of aliasing, while still maintaining adequate data completeness for monitoring applications.
3Quantity of substance
If low pulse repetition rates are used, then data volume is reduced, but data acquisition completeness may be compromised
Solution Approach 1:
The patent applies the extraction principle by selectively acquiring only the essential acoustic information at low pulse repetition rates, rather than continuously acquiring all possible data. This selective extraction approach reduces data volume while maintaining the completeness needed for acoustic level monitoring, by taking out only the critical measurement points required for the application.
4Measurement precision
If conventional DAS processing is used, then processing accuracy is maintained, but processing complexity increases for long distance monitoring
Solution Approach 1:
By using periodic action with low pulse repetition rates, the patent simplifies the processing requirements for long distance monitoring. The reduced sampling rate decreases the computational burden and processing complexity while maintaining adequate accuracy for acoustic level determination, as the system only needs to process the essential periodic data points rather than continuous high-rate streams.
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 enables efficient monitoring of acoustic levels with lower data acquisition rates, reducing data volume and avoiding aliasing, thus facilitating longer distance monitoring with improved accuracy and reduced processing complexity.
Implementation Method 1
the photons may be elastically scattered in a phenomenon known as Rayleigh scattering
Implementation Method 2
processes the low frequency component of the DAS signal, allowing for reduced data volume and minimizing aliasing, enabling accurate acoustic level monitoring over extended distances by separating temperature and acoustic components through non-linear frequency mixing
Data Source
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AI summary
A distributed acoustic sensing system and a method of obtaining acoustic levels using the distributed acoustic sensing system are described. The distributed acoustic sensing system includes an optical fiber, a light source to inject light into the optical fiber, and a photodetector to sample a DAS signal in each section of one or more sections of the optical fiber resulting from two or more points within the section on the optical fiber over a period of time. The system also includes a processor to process only a low frequency portion of the DAS signal to obtain the acoustic levels at each of the one or more sections on the optical fiber over the period of time, the low frequency portion of the DAS signal being less than 10 Hz.