Fiber Optic CO2 Sensor Using Long Period Gratings
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Solution Overview
Problem
Existing technologies are not well-suited for densely spaced, shallow subsurface CO2 measurements, detection of CO2 fluxes, leak identification in wellbores, and subsea environments, and are economically impractical for distributed Monitoring, Measurement, and Verification (MMV) of CO2 geosequestration sites.
Innovation Solution
The development of fiber-optic sensors with optical fibers incorporating long period gratings, Fabry-Perot interferometers, and Mach-Zehnder interferometers, coated with materials that enhance sensitivity to CO2 concentrations, allowing for simultaneous or sequential wavelength detection and deployment in arrays for large-scale environmental coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MMV technologies are used for CO2 geosequestration monitoring, then measurement capability is provided, but capital and operating costs become impractically high
Solution Approach 1:
The patent replaces conventional mechanical/electronic sensing systems with fiber-optic based sensing technology. The fiber-optic sensors use optical principles (evanescent field interaction, refractive index changes) to detect CO2 concentrations, eliminating the need for complex electronic components and reducing both capital and operating costs while maintaining measurement precision.
Solution Approach 2:
The patent utilizes changes in refractive index as a parameter to detect CO2 concentrations. By monitoring the refractive index changes in the surrounding medium that affect the optical properties of the fiber, the system achieves accurate CO2 measurement through a simple, cost-effective optical parameter rather than complex mechanical or electronic measurements.
2Area of stationary object
If densely spaced sensors are deployed for shallow subsurface CO2 measurements, then measurement coverage is improved, but system complexity and cost increase
Solution Approach 1:
The fiber-optic sensor system serves multiple functions simultaneously: it can detect CO2 concentrations, monitor refractive index changes, and provide distributed sensing along the fiber length. This multi-functionality allows densely spaced sensors to be deployed for comprehensive coverage without proportionally increasing system complexity, as the same optical infrastructure supports multiple measurement objectives.
Solution Approach 2:
The patent employs distributed fiber-optic sensing where the fiber itself is segmented into multiple sensing points along its length. This allows densely spaced measurement locations to be achieved by simply extending the fiber network, rather than deploying discrete complex sensor units at each location, thereby reducing overall system complexity while maintaining high spatial resolution.
3Measurement precision
If fiber-optic sensors with multiple interrogation wavelengths are used, then CO2 detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent employs periodic wavelength modulation in the interrogation system, where multiple wavelengths are applied in a sequential or modulated manner rather than simultaneously. This periodic action allows accurate CO2 detection through multi-wavelength analysis while simplifying the interrogation device architecture compared to systems requiring simultaneous multi-wavelength generation and detection.
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
These sensors provide accurate and cost-effective monitoring of CO2 concentrations and fluxes, enabling efficient detection of leaks and storage verification across various environments, reducing capital and operating costs while improving measurement precision.
Implementation Method 1
sensors are responsive to the refractive index of a medium that surrounds (as used herein, 'surrounding refractive index' or 'SRI') the fiber and thereby to the concentration of an analyte such as CO2 in the medium
Implementation Method 2
Refractive indices can be detected using sensors that include in-fiber Bragg gratings, long period gratings
Implementation Method 3
Refractive indices can be detected using sensors that include in-fiber Bragg gratings, long period gratings, Fabry-Perot interferometers
Implementation Method 4
Refractive indices can be detected using sensors that include in-fiber Bragg gratings, long period gratings, Fabry-Perot interferometers, Mach-Zehnder interferometers
Data Source
AI summary
Fiber optic sensors include sensor regions in which an optical phase is modulated by an analyte to be detected. A long period fiber grating (LPG) is coupled to a coating that is arranged to selectively interact with the analyte. The resulting phase change is detected based on a transmission spectrum associated with the LPG so that analyte is detected and quantified. A plurality of such sensors is distributed along a fiber to form a sensor array that can be situated to detect analyte at a plurality of discrete regions.