Interleaved Fiber Bragg Gratings for High-Resolution Downhole Sensing
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Solution Overview
Problem
Current technologies for monitoring borehole structural and environmental conditions in hydrocarbon production are limited by low accuracy and high costs, particularly in achieving precise measurements as a function of depth.
Innovation Solution
An optical fiber system with interleaved fiber Bragg gratings and an optical interrogator that emits a frequency domain light signal with a swept wavelength and chirp, allowing for precise measurement of resonant wavelength shifts to determine downhole properties such as temperature, pressure, and strain, with improved spatial resolution through wave division multiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fiber Bragg gratings are spaced closely to improve spatial resolution, then measurement accuracy improves, but adjacent gratings with similar resonant wavelengths interfere with each other
Solution Approach 1:
The patent applies parameter changes by assigning different resonant wavelengths to adjacent fiber Bragg gratings, creating an interleaved wavelength pattern. This wavelength differentiation allows closely spaced gratings to be distinguished without signal interference, resolving the contradiction between spatial resolution and signal interference.
Solution Approach 2:
The patent transitions from spatial differentiation alone to wavelength-spatial differentiation by introducing the wavelength dimension. Instead of relying solely on physical separation, the system uses wavelength multiplexing to distinguish adjacent gratings, enabling closer spacing while maintaining measurement accuracy.
2Measurement precision
If the optical interrogator sweeps wavelength slowly to improve measurement accuracy, then resonant wavelength shift detection improves, but the measurement time increases
Solution Approach 1:
The patent implements periodic action through the chirped pulse sequence, where the optical interrogator emits repeated pulses with linearly increasing frequency. This periodic sweeping allows multiple measurements to be taken efficiently, improving signal-to-noise ratio and measurement accuracy without proportionally increasing total measurement time.
Solution Approach 2:
The patent applies preliminary action by pre-sweeping the wavelength range before actual measurement. The chirped pulse sequence performs a preliminary frequency sweep that prepares the system for accurate resonant wavelength detection, enabling faster subsequent measurements with maintained 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
This approach enables increased spatial resolution and accuracy in monitoring borehole conditions, allowing for closer spacing of fiber Bragg gratings and improved shape sensing of structures, thereby enhancing the efficiency and cost-effectiveness of hydrocarbon production.
Implementation Method 1
each section having a first fiber Bragg grating having a first resonant wavelength and a second fiber Bragg grating having a second resonant wavelength
Implementation Method 2
emit a frequency domain light signal into the optical fiber, the frequency domain light signal having a swept wavelength for a first time duration and a chirp having a modulation of amplitude with a varying of wavelength
Implementation Method 3
transform the frequency domain return signal into a time domain in order to determine the resonant wavelength shift of each fiber Bragg grating and the corresponding location of each interrogated fiber Bragg grating
Data Source
AI summary
A downhole property measurement apparatus includes an optical fiber having a series fiber Bragg gratings with interleaved resonant wavelengths such that adjacent fiber Bragg gratings have different resonant wavelengths and a difference between adjacent resonant wavelengths is greater than a dynamic wavelength range of each of the adjacent fiber Bragg gratings. An optical interrogator is in optical communication with the optical fiber and configured to emit a frequency domain light signal having a swept wavelength for a first time duration and a chirp having a modulation of amplitude with a varying of wavelength for a second time duration that is less than the first time duration. A return light signal is transformed by the optical interrogator into a time domain to determine a resonant wavelength shift and corresponding location of each of the gratings. A processor converts the resonant wavelength shifts into the downhole property.