IOFDR Fiber Bragg Grating Array for Extended Downhole Sensing
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Solution Overview
Problem
Current technologies for monitoring borehole structural and environmental conditions in hydrocarbon production lack accuracy and cost-effectiveness, particularly in sensing downhole properties over long distances with existing optical fiber systems.
Innovation Solution
An optical sensing system utilizing fiber Bragg gratings and an optical interrogator with Incoherent Optical Frequency Domain Reflectometry (IOFDR) for precise measurement of downhole properties, including temperature, strain, and pressure, by employing a chirped optical signal and multiple sections of fiber Bragg gratings with distinct resonant wavelengths to enhance measurement accuracy and range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single resonant wavelength is used for fiber Bragg gratings, then the system is simpler, but the measurement range and accuracy are limited
Solution Approach 1:
The optical fiber is divided into multiple sections, each containing fiber Bragg gratings with distinct resonant wavelengths. This segmentation allows the system to measure different downhole conditions at different locations along the borehole, extending the measurement range and improving accuracy without requiring a single complex grating design
Solution Approach 2:
Each section of the optical fiber is assigned a specific resonant wavelength tailored to the measurement requirements of that particular downhole zone. This local customization of grating properties enables optimized measurement accuracy for different environmental conditions at different depths
2Length of stationary object
If the measurement range is extended over long distances, then more downhole coverage is achieved, but signal degradation occurs
Solution Approach 1:
By dividing the optical fiber into multiple sections with distinct resonant wavelengths, the system can process signals from different distances simultaneously. The frequency domain reflectometry technique processes each wavelength component separately, preventing signal degradation from accumulating across the entire long distance
Solution Approach 2:
The system transitions from time-domain to frequency-domain signal processing. By using frequency domain reflectometry with multiple resonant wavelengths, the system can distinguish signals from different distances based on their frequency characteristics rather than relying solely on time-of-flight, thereby maintaining signal quality over extended measurement ranges
3Measurement precision
If multiple fiber Bragg gratings with different resonant wavelengths are used, then measurement range and accuracy are improved, but processing time increases
Solution Approach 1:
The system uses continuous wave (CW) laser illumination combined with frequency domain reflectometry to simultaneously interrogate all fiber Bragg grating sections. This continuous measurement approach eliminates the need for sequential scanning of different wavelengths, maintaining high measurement accuracy while minimizing processing time
Solution Approach 2:
By transforming the measurement approach from time-domain sequential detection to frequency-domain simultaneous detection, the system can extract information from multiple resonant wavelengths concurrently. The frequency domain processing allows parallel analysis of all grating sections, significantly reducing the time penalty associated with measuring multiple wavelengths
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
The system provides accurate and cost-effective monitoring of downhole properties over extended distances, overcoming limitations of signal degradation and processing time, enabling real-time data acquisition and alerting for threshold exceedances.
Implementation Method 1
Each fiber Bragg grating is configured to reflect a specific resonant wavelength of light
Implementation Method 2
An optical interrogator illuminates the optical fiber with a frequency domain light signal having a chirped amplitude and a swept wavelength
Data Source
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AI summary
An apparatus for performing a measurement of a downhole property includes an optical fiber having a first section that has a first set of fiber Bragg gratings with a first resonant wavelength inscribed therein and a second section that has a second set of fiber Bragg gratings with a second resonant wavelength different from the first resonant wavelength inscribed therein. The second section is in series with the first section. An optical interrogator emits a swept-wavelength frequency domain light signal having varying wavelength amplitude modulation into the optical fiber, receives a frequency domain return light signal, and transforms the frequency domain return signal into a time domain to determine a resonant wavelength shift of each fiber Bragg grating and the corresponding location of each interrogated fiber Bragg grating. A processor converts the resonant wavelength shift of each interrogated fiber Bragg grating into the downhole property measurement.