DAS Fiber Optic Assembly with Coated Sections for Broadside Wave Detection
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Solution Overview
Problem
Current Distributed Acoustic Sensing (DAS) systems are primarily sensitive to axial strain and become less sensitive or fail to detect acoustic signals traveling at angles close to perpendicular to the fiber axis, limiting their effectiveness in seismic and microseismic applications.
Innovation Solution
A DAS fiber optic assembly comprising two lengths of optical fibers with different directional acoustic sensitivities, achieved through varying coatings such as acrylate and copper, which alter the Young's Modulus or Poisson's ratio, allowing for enhanced detection of radial strain and broadside waves by converting radial strain into axial strain for improved sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single optical fiber with standard coating is used for DAS, then axial strain detection is effective, but radial strain detection sensitivity is insufficient
Solution Approach 1:
The optical fiber is divided into multiple sections with different coating properties along its length. Each section has coatings with specific Young's Modulus and Poisson's ratio characteristics that enable differential response to radial and axial strains, allowing the system to detect both strain components effectively
Solution Approach 2:
Different sections of the optical fiber are equipped with locally varied coating properties. The coating material composition, thickness, or structure changes at specific locations to create sections with distinct mechanical characteristics, enabling each section to respond differently to applied strains based on local requirements
2Reliability
If acoustic signals travel at perpendicular angles to the fiber axis, then broadside wave detection is required, but standard DAS systems become much less sensitive or fail to detect
Solution Approach 1:
The optical fiber assembly incorporates composite coating structures with materials having different mechanical properties. These composite coatings create sections that can detect both axial and radial strain components, enabling reliable broadside wave detection while maintaining sensitivity through the differentiated material responses
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 solution enables more sensitive detection of acoustic signals traveling normal to the fiber axis, allowing for better seismic data acquisition and subsurface imaging by distinguishing between axial and radial strain components, thereby improving the sensitivity and accuracy of seismic data recording.
Implementation Method 1
distributed measurement of optical path length changes along an optical fiber by measuring backscattered light from a laser pulse input into the fiber
Implementation Method 2
the Young's Modulus or Poisson's ratio of the first length of coated fiber is less than the Young's Modulus or Poisson's ratio of the second length of coated fiber
Data Source
AI summary
A Distributed Acoustic Sensing(DAS) fiber optical assembly comprises adjacent lengths of optical fiber A, B with different directional acoustic sensitivities, for example by providing the first length of optical fiber A with a first coating 35, such as acrylate, and the second length of optical fiber B with a second coating 36, such as copper, wherein the first and second coatings 35 and 36 may be selected such that the Poisson's ratio of the first length of coated fiber A is different from the Poisson's ratio of the second length of coated fiber B. The different Poisson's ratios and/or other properties of the adjacent lengths of optical fiber A and B improve their directional acoustic sensitivity and their ability to detect broadside (radial) acoustic waves.