Fiber Optic Magnetic Field Sensing via Lorentz Force
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electronic tools for magnetic field sensing in oil field exploration are temperature-sensitive, have high loss, slow speeds, and lack durability, making permanent installation difficult, and are limited to single-point measurements.
Innovation Solution
A fiber-optic magnetic field sensing system using a strain-sensing fiber coupled with a conducting strip, where the induced Lorentz force causes strain, measured by a distributed feedback fiber laser, enabling accurate and robust distributed magnetic field measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electronic tools are used for magnetic field sensing, then magnetic field measurement is achieved, but temperature sensitivity and high loss make them unsuitable for permanent downhole installation
Solution Approach 1:
The patent replaces electronic sensing tools with a fiber-optic-based magnetic field sensing system. The fiber optic cable transmits light signals that are modulated by magnetic field effects on the surrounding medium, eliminating the temperature sensitivity and signal loss issues inherent in electronic tools while maintaining magnetic field measurement capability
Solution Approach 2:
The system changes the operating parameters by using optical signals instead of electrical signals for sensing. The magnetic field induces changes in the optical properties of the surrounding medium (such as refractive index), which are then detected by the fiber optic system, providing temperature-stable measurements with low signal loss
2Measurement precision
If electronic tools are used for magnetic field sensing, then single-point measurement is achieved, but distributed measurements require multiple tools increasing complexity
Solution Approach 1:
The fiber optic cable is segmented into multiple sensing zones along its length, each capable of detecting magnetic field changes independently. By dividing the sensing function into discrete segments along the fiber, the system achieves distributed measurements without requiring multiple separate tools, reducing complexity while maintaining measurement accuracy
Solution Approach 2:
A single fiber optic cable performs multiple sensing functions at different locations simultaneously. The fiber acts as a universal sensing element that can measure magnetic fields at multiple points along its length, eliminating the need for multiple specialized tools and simplifying the overall system configuration
3Productivity
If electronic tools are used for magnetic field sensing, then measurement capability is achieved, but slow speeds and lack of durability make permanent installation difficult
Solution Approach 1:
The patent replaces electronic sensing systems with an optical fiber-based system that uses light propagation and optical modulation. This substitution enables faster measurement speeds through optical signal transmission and provides superior durability for permanent installation, as fiber optic cables are resistant to corrosion, heat, and mechanical damage in downhole environments
Solution Approach 2:
The sensing system uses composite material structures including the fiber optic cable combined with magnetic field-responsive materials or coatings. This composite approach enhances both the speed of optical signal transmission and the durability of the sensing element in harsh downhole conditions, enabling permanent installation with high measurement throughput
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 high-speed, low-loss, and temperature-stable magnetic field sensing capable of permanent downhole deployment, enabling efficient monitoring of magnetic fields in complex wellbores and allowing for early detection of waterfront movement.
Implementation Method 1
A conducting strip is coupled to a strain-sensing fiber to form a composite structure. A current is generated on the conducting strip. When a magnetic field is present, a Lorentz force is induced that causes a deflection of the conducting strip and a corresponding strain on the strain-sensing fiber.
Data Source
AI summary
A method and apparatus for magnetic sensing is described. The apparatus includes a strain-sensing fiber coupled to a conducting strip. The strain-sensing fiber may be, for example, a distributed feedback fiber with Bragg gratings. A current may be induced to flow on the conducting strip by electrically coupling a photodiode to the conducting strip and then activating a laser optically coupled to the photodiode. In the presence of a magnetic field, a Lorentz force will be exerted on the conducting strip, causing a displacement of the conducting strip that will induce strain on the strain-sensing fiber. The strain on the strain-sensing fiber may be measured by laser-pumping the strain-sensing fiber and measuring the reflected waves. The measured strain may be used to calculate the magnitude of the magnetic field. Multiple strain-sensing fibers may be optically coupled in series and deployed into a borehole for distributed magnetic field measurements. The magnetic field measurements may be used to determine the resistivity of formations surrounding the borehole and, for example, to monitor the movement of relatively-low resistivity water fronts.