Optical Fiber Feedthrough Integrating FBG for Downhole Pressure Gauges
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Solution Overview
Problem
Existing pressure gauge devices for subterranean operations face challenges in accurately measuring downhole pressure and temperature due to the need for separate sensors and space constraints, which affect the sensitivity and integrity of the measurements.
Innovation Solution
A pressure gauge device that incorporates a Fiber Bragg Grating (FBG) to measure both pressure and temperature, with a feedthrough device that minimizes thermal resistance and tension in the fiber optic line, allowing for remote diagnostics of the gauge's condition and integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the FBG is suspended with slack to avoid tension, then the FBG is protected from elastic strain, but the device size increases due to additional space requirements
Solution Approach 1:
The patent combines the FBG mounting structure with the pressure sensor housing, integrating the FBG support directly into the existing device architecture. This eliminates the need for separate suspension mechanisms and slack accommodation space, thereby reducing overall device volume while maintaining FBG protection from tension.
Solution Approach 2:
The FBG is nested within the pressure sensor housing structure, with the grating section positioned inside the sealed cavity. This nesting approach allows the FBG to be protected and positioned accurately without requiring additional external support structures, thus minimizing device size.
2Measurement precision
If the FBG is coupled to a metallic structure to increase temperature sensitivity, then temperature measurement sensitivity improves, but the device complexity increases
Solution Approach 1:
The pressure sensor housing serves multiple functions: it provides mechanical support for the FBG, acts as a thermal coupling structure to enhance temperature sensitivity, and maintains the sealed environment. This multi-functionality eliminates the need for separate temperature sensing structures, thereby reducing device complexity while improving temperature measurement capability.
Solution Approach 2:
The patent utilizes the thermal expansion properties of the metallic housing structure to enhance FBG temperature sensitivity. As the metal housing expands or contracts with temperature changes, it transfers thermal strain to the FBG, amplifying the temperature measurement signal without requiring additional active heating or cooling mechanisms.
3Temperature
If the FBG is placed proximate to the pressure sensor, then thermal coupling is improved, but space availability is constrained
Solution Approach 1:
The patent creates a localized thermal coupling zone within the pressure sensor housing where the FBG is positioned in direct thermal contact with the pressure sensing elements. This local optimization of thermal coupling allows efficient temperature measurement without requiring the entire device to be redesigned for space accommodation.
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
Enhances temperature sensitivity and allows for remote monitoring of the pressure gauge's condition, detecting potential failures and ensuring accurate measurements by maintaining the FBG proximate to the pressure sensor and minimizing thermal resistance.
Implementation Method 1
The temperature sensor of the fiber gauge may consist of a Fiber Bragg Grating (FBG) which can be placed in line with the pressure sensor... the FBG's response to a change in temperature includes the effect of the thermal response of the host material to which it is coupled... typically) larger Coefficient of Thermal Expansion (CTE) of metals compared to silica
Implementation Method 2
a pressure sensor and a temperature sensor... a single fiber may be used to interrogate both the pressure sensor and the temperature sensor
Data Source
AI summary
Methods and systems for effectively sealing a fiber optic line to a pressure gauge device are disclosed. A pressure gauge device has an outer body, a reference volume within the outer body and a pressure sensor having a first side and a second side. The first side of the pressure sensor is exposed to a pressure inlet and the second side of the pressure sensor is exposed to the reference volume. A fiber optic line is coupled to the pressure gauge device using a feedthrough device. The fiber optic line comprises a first fiber optic line portion located within the feedthrough device, a second fiber optic line portion located within the reference volume and a third fiber optic line portion located within a cable located outside the pressure gauge device and coupled to the feed through device. The first fiber optic line portion comprises a first Fiber Bragg Grating (“FBG”).