Fiber Optic Distributed Acoustic Sensing for Seismic Signal Processing
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Solution Overview
Problem
Current seismic geophysical surveying methods, particularly in wellbores and surface applications, face challenges with geophone arrays being expensive, limited in number, and requiring relocation, which can lead to inaccurate data alignment and environmental changes, while fiber optic distributed acoustic sensors (DAS) offer advantages but require improved signal processing to enhance signal-to-noise ratio and data quality.
Innovation Solution
A fiber optic distributed sensing apparatus that acquires diversity samples of backscattered radiation, processes them into diversity channels, correlates these with seismic stimulus signals, and combines them to improve the overall measurement signal, using a quality metric to select high-quality data and reduce noise, thereby enhancing the signal-to-noise ratio and data accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If geophone arrays are used for seismic surveys, then measurement capability is provided, but cost increases and the arrays require relocation which leads to data alignment inaccuracies and environmental changes
Solution Approach 1:
The patent replaces mechanical geophone arrays with optical fiber-based distributed acoustic sensing (DAS) systems. The optical fiber acts as a continuous sensing medium along the wellbore, eliminating the need for discrete mechanical sensors that require positioning and alignment. This substitution provides continuous measurement capability while reducing deployment complexity and cost.
Solution Approach 2:
The optical fiber serves multiple functions: it acts as both the sensing element for acoustic measurements and as a permanent infrastructure that can be reused for multiple surveys. The fiber can be deployed once and used repeatedly for different seismic survey configurations, providing universal applicability across multiple measurement campaigns.
2Area of stationary object
If geophone arrays are relocated for different survey sections, then complete area coverage is achieved, but data alignment accuracy decreases and environmental conditions change
Solution Approach 1:
The patent segments the optical fiber into multiple sensing zones along the wellbore depth, allowing different sections to be activated for different survey configurations. The fiber is divided into discrete measurement intervals that can be independently addressed, enabling complete area coverage while maintaining fixed sensor positions for accurate data alignment.
Solution Approach 2:
The optical fiber is deployed and installed in the wellbore before any seismic surveys are conducted. This preliminary deployment establishes a permanent, fixed sensing infrastructure that eliminates the need for repeated installation and relocation operations, ensuring consistent positional references for accurate data alignment across multiple surveys.
3Ease of manufacture
If fiber optic DAS is used instead of geophones, then deployment cost decreases and permanent installation is possible, but signal-to-noise ratio requires improvement
Solution Approach 1:
The patent combines multiple diversity samples from different spatial locations along the optical fiber into a single enhanced measurement signal. By merging signals from adjacent sensing zones and applying coherent stacking, the system improves the signal-to-noise ratio while maintaining the cost advantages of optical fiber deployment.
Solution Approach 2:
The system applies correlation processing between the measured acoustic signals and the known seismic source signature. This feedback mechanism enhances the desired signal by comparing it against the expected source characteristics, thereby improving signal-to-noise ratio and measurement reliability.
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 improves the signal-to-noise ratio and data quality in seismic surveys by effectively correlating and combining measurement signals from fiber optic sensors, allowing for more accurate and reliable monitoring of acoustic disturbances in wellbores and surface applications.
Implementation Method 1
Radiation which is backscattered from within the optical fibre is detected and analysed to reveal information about acoustic stimuli acting on the optical fibre
Implementation Method 2
seismic source for producing a seismic stimulus... capable of injecting low frequency vibrations into the earth
Data Source
AI summary
The present invention relates to an apparatus for use in geophysical surveying. Geophysical surveying typically involves stimulating an area of interest with a seismic source (204) and detecting the response in a sensor array. The application describes a fiber optic distributed sensing apparatus having a source (112) of electromagnetic radiation for repeatedly launching interrogating electromagnetic radiation into an optic fiber (104) deployed in said of area interest, a sampling detector (116) for sampling radiation back-scattered from the fiber; and a processor (108) arranged to process the back-scattered radiation to provide, for each of a plurality of longitudinal sensing portions of optic fiber, an indication of any incident acoustic signals affecting that sensing portion. The sampling detector is arranged to acquire a plurality of diversity samples for each said longitudinal sensing portion. The processor is configured process the diversity samples in diversity channels to determine a measurement signal indicative of any acoustic disturbance; correlate the measurement signal from each channel with a signal indicative of the seismic stimulus applied; and combine the correlated measurement signals to provide an overall measurement signal for the longitudinal sensing portion. The processor may apply a quality metric to the correlated data before performing the combination based on the quality metric. By correlating the individual diversity channels with the stimulus signal prior to performing the analysis of the measurement signal for a particular longitudinal section of optic fiber, the signal to noise ratio can be improved.