Downhole Reference Fiber Coil for Temperature and Strain Calibration
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Solution Overview
Problem
Subsea operations face challenges in optical fiber sensing due to signal quality issues in distributed fiber optic sensing systems, particularly with wavelength-dependent attenuation across connectors, splices, and optical feedthrough systems, leading to inaccurate temperature and strain measurements.
Innovation Solution
A coil of reference fiber, made from the same type of fiber as the sensing fiber, is positioned to provide a known temperature and strain, enabling real-time calibration and accurate measurement by differentiating between temperature and strain using Brillouin sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If distributed fiber optic sensing is used to obtain real-time temperature or strain data along a wellbore, then measurement coverage and resolution are improved, but signal quality deteriorates due to wavelength-dependent attenuation across connectors and splices
Solution Approach 1:
A reference fiber coil is introduced as an intermediary element between the sensing fiber and the measurement system. This reference fiber coil provides a known thermal and strain response that acts as a mediator to calibrate and compensate for the wavelength-dependent attenuation and environmental effects affecting the sensing fiber, thereby maintaining measurement accuracy despite signal quality degradation
Solution Approach 2:
The system uses the reference fiber coil to provide feedback information about the thermal and strain conditions. By comparing the known response of the reference fiber with the sensing fiber measurements, the system can dynamically adjust and compensate for attenuation variations, maintaining reliable measurements even when signal quality deteriorates due to connector and splice effects
2Length of moving object
If fiber optic cables are extended to reach deeper well sections, then measurement coverage is improved, but signal quality deteriorates due to increased attenuation and environmental effects
Solution Approach 1:
The reference fiber coil serves as a mediator that provides known thermal and strain reference points along the extended fiber network. This allows the system to compensate for attenuation and environmental effects over long distances, maintaining measurement precision even as fiber cable length increases to reach deeper well sections
Solution Approach 2:
The system changes the measurement approach by using the reference fiber coil to establish known parameter relationships between temperature, strain, and optical signal characteristics. This allows the system to account for attenuation variations and environmental effects when interpreting measurements from extended fiber cables, maintaining accuracy despite increased cable length
3Measurement precision
If calibration is performed periodically to account for changing attenuation characteristics, then measurement accuracy is maintained, but system complexity and data interpretation difficulty increase
Solution Approach 1:
The reference fiber coil acts as a stable intermediary that provides consistent known thermal and strain responses throughout the wellbore. This eliminates the need for complex periodic recalibration procedures, as the reference coil maintains stable reference points that simplify data interpretation while ensuring measurement accuracy
Solution Approach 2:
The reference fiber coil provides self-contained calibration information that is inherently stable and does not require external intervention or complex recalibration procedures. The system can use the reference coil's known characteristics to automatically compensate for attenuation effects, reducing operational complexity while maintaining measurement precision
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 coil of reference fiber allows for real-time calibration, overcoming signal distortions and inaccuracies, ensuring accurate temperature and strain measurements even at extended distances and varying environmental conditions.
Implementation Method 1
Measurements of the Brillouin frequency along sensing fiber regions can be interpreted in terms of strain, temperature, or pressure using Brillouin optical time domain reflectometry (BOTDR)
Data Source
AI summary
A method may include receiving interrogation data from a sensing fiber via a coil of reference fiber of a same type of fiber as the sensing fiber. The sensing fiber may be coupled in series with the coil of reference fiber. The method may also include receiving a known temperature and a known strain from the coil of reference fiber and outputting the known temperature, the known strain, and the interrogation data for use in calibrating a measurement of the interrogation data.