Helical Optical Cable Structure for Omnidirectional Seismic Sensing
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Solution Overview
Problem
Existing optical cables used for detecting underground resources using seismic waves face challenges such as poor response to seismic waves incident perpendicular to the cable, nonlinear response to transverse waves, insufficient cable strength and heat resistance, and unsuitable long-term installation methods.
Innovation Solution
An optical cable structure featuring an optical fiber surrounded by helically wound first steel wires and a flexible material, with a specific winding angle and strain ratio parameter, forming an annular body to enhance sensitivity and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the optical fiber is mounted substantially in the axial direction of the cable, then the cable structure is simple, but the optical fiber does not respond to seismic waves incident perpendicular to the cable
Solution Approach 1:
The optical fiber is mounted helically around the cable axis rather than axially, changing the mounting dimension from linear to three-dimensional spiral configuration. This enables the fiber to detect seismic waves incident from multiple directions including perpendicular directions, resolving the contradiction between structural simplicity and detection reliability
2Reliability
If the optical fiber is helically mounted on the cable, then the seismic wave detection capability is improved, but the response to transverse waves becomes nonlinear and difficult to use for quantitative analysis
Solution Approach 1:
The helical pitch and winding angle of the optical fiber are optimized to specific parameter ranges. By controlling these geometric parameters, the fiber's response to transverse waves is linearized, enabling both improved seismic wave detection capability and quantitative analysis capability simultaneously
3Measurement precision
If the cable body size is increased, then the sensor resolution increases, but the space for oil well installation becomes insufficient
Solution Approach 1:
The cable body dimensions are optimized to a specific size range that balances sensor resolution requirements with installation space constraints. The optical fiber's helical parameters are adjusted to achieve high resolution within a compact cable body, resolving the contradiction between measurement precision and volume
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 optical cable effectively detects seismic waves irrespective of incident direction, improves sensitivity, and ensures robustness and suitability for long-term installations.
Implementation Method 1
technology of acquiring an acoustic wave, i.e., a strain change amount, at each point on an optical fiber in a distributed manner by distributed acoustic sensing (DAS)
Implementation Method 2
a plurality of first steel wires helically wound so as to surround the optical fiber, and a flexible material surrounding the optical fiber and the plurality of first steel wires
Data Source
Figure 1A~2B
Figure 3A~3C
Figure 4~5
AI summary
An optical cable (31) includes: a stress wave detection optical cable (30) having an optical fiber (7) and a plurality of first steel wires (8) which are helically wound so as to surround the optical fiber (7) and which are surrounded by a flexible material (9); and second steel wires (32) different from the first steel wires (8). The stress wave detection optical cable (30) and the plurality of second steel wires (32) are helically wound to form one annular body as a whole, and a winding angle (α) of the stress wave detection optical cable (30) with respect to the axis is determined by a property value prescribed by Lamé constants of the flexible material (9).