Cane-Based Bragg Grating Sensors for Well-Bore Temperature Monitoring
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Solution Overview
Problem
Distributed Temperature Sensing (DTS) systems face challenges with weak signal reflection, especially in deep wells, and Array Temperature Sensing (ATS) systems struggle with strain sensitivity and fluid/gas ingress affecting measurement accuracy.
Innovation Solution
The use of cane-based Bragg grating sensors in a single conduit with large diameter optical waveguides, protected by a metal plating and armor layer, reduces strain sensitivity and fluid/gas ingress, enhancing signal reflection and measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Distributed Temperature Sensing (DTS) systems are used to monitor temperature along the length of a well, then temperature monitoring capability is provided, but the signal reflected back is weak and difficult to read, especially in deep wells
Solution Approach 1:
The waveguide is segmented into multiple sections, each containing a Bragg grating sensor at specific locations. This segmentation allows for discrete reflection points that return stronger signals compared to distributed sensing, while still providing temperature monitoring along the entire length of the well.
Solution Approach 2:
Bragg gratings are placed periodically or at specific intervals along the waveguide, creating periodic reflection points. This periodic structure enables the system to return stronger reflected signals at known locations, improving signal strength while maintaining temperature monitoring capability.
2Loss of energy
If Array Temperature Sensing (ATS) systems with Bragg gratings are used to overcome weak signal issues, then signal reflection strength is improved, but the system becomes sensitive to strain changes that cause errors in temperature measurement
Solution Approach 1:
The strain sensitivity problem is addressed by extracting or removing the strain effect from the measurement. This is achieved through differential measurement techniques where strain effects are separated and eliminated, leaving only temperature-induced wavelength shifts for accurate temperature measurement.
Solution Approach 2:
Different sections of the waveguide or different Bragg gratings are designed with different properties to selectively measure temperature while being insensitive to strain. By creating local variations in grating characteristics, the system can distinguish between temperature and strain effects at different locations.
3Ease of operation
If traditional fiber optic cables are used in the ATS system, then the system can be installed in the well-bore, but production fluids and gases cause significant increases in fiber loss and refractive index, affecting measurement accuracy
Solution Approach 1:
A protective coating or sheath is applied to the waveguide to create a barrier against fluid and gas ingress. This flexible protective layer prevents production fluids from reaching the glass optical fiber, maintaining stable refractive index and low loss characteristics while allowing the system to be installed in the well-bore environment.
Solution Approach 2:
The waveguide structure uses composite materials that are inherently resistant to hydrogen and fluid ingress. This may include metal-plated waveguides or waveguides with specialized coatings that prevent chemical interaction with production fluids, ensuring long-term reliability and measurement accuracy in harsh well-bore conditions.
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 provides improved temperature monitoring with increased signal strength, reduced strain errors, and protection from fluid/gas ingress, enabling accurate temperature measurements over long distances with high resolution and immunity to hydrogen-induced changes.
Implementation Method 1
several Bragg gratings are placed in a waveguide, such as a fiber. The gratings can be at any desired location along the waveguide. Advantageously, a reflected signal from the grating is greater than that of the DTS system.
Implementation Method 2
A DTS system utilizes an optical waveguide, such as an optical fiber, as a temperature sensor. In a typical DTS system, a laser or other light source at the surface of the well transmits a pulse of light into a fiber optic cable installed along the length of the well.
Implementation Method 3
The effects of these strain changes are generally indistinguishable from those of changes in temperature and cause errors in the temperature measurement.
Implementation Method 4
A further need exists for methods and assemblies to provide the ATS system that is protected from the ingress of fluids and gases.
Data Source
AI summary
Methods and apparatus enable monitoring conditions in a well-bore using multiple cane-based sensors. The apparatus includes an array of cane-based Bragg grating sensors located in a single conduit for use in the well-bore. For some embodiments, each sensor is located at a different linear location along the conduit allowing for increased monitoring locations along the conduit.