DAS Seismic Profile De-spiking via Quadrature Phase Analysis
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Solution Overview
Problem
Distributed Acoustic Sensing (DAS) systems for vertical seismic profiling face noise issues due to transient or permanent material property variations in optical fibers, leading to signal degradation and inaccurate seismic data.
Innovation Solution
The implementation of a DAS-based VSP system that uses quadrature modulated backscatter responses processed by a phase analyzer, combined with a threshold filter to remove noise and enhance signal quality, allowing for accurate seismic profiling by correlating the filtered seismic response with recorded seismic signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DAS systems utilize Rayleigh backscatter of laser light energy to detect acoustic/seismic energy, then spatial detection capability is improved, but noise from material property variations in optical fibers degrades signal quality
Solution Approach 1:
The patent extracts and removes spiky noise portions from the DAS signal that exceed a calculated threshold. The threshold is determined based on the standard deviation of the signal, allowing selective removal of abnormal noise while preserving legitimate seismic signals. This extraction principle directly addresses the contradiction by eliminating the harmful noise components without affecting the underlying seismic data.
Solution Approach 2:
The patent changes the parameter of signal threshold by calculating it dynamically based on signal statistics (mean and standard deviation). This adaptive threshold parameter allows the system to distinguish between normal signal variations and spiky noise, resolving the contradiction by providing a dynamic criterion for noise rejection while maintaining sensitivity to legitimate seismic events.
2Reliability
If trace fading is removed through filtering, then signal quality is improved, but legitimate seismic signals may be lost
Solution Approach 1:
The patent employs feedback by using the statistical properties (mean and standard deviation) of the signal itself to determine the threshold for noise removal. This self-referential approach allows the system to adapt to the specific characteristics of each signal, ensuring that the filtering criterion is optimized for the actual data being processed rather than using fixed thresholds that might eliminate legitimate signals.
Solution Approach 2:
The patent changes the threshold parameter dynamically based on signal statistics rather than using a fixed value. By calculating the threshold as a function of the signal's mean and standard deviation, the system adapts to varying signal conditions, maintaining reliability in noise removal while preserving legitimate seismic signals that fall within the dynamically adjusted threshold range.
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 significantly improves the accuracy and reliability of seismic profiling by minimizing noise and preserving essential seismic data, resulting in more precise seismic profiles.
Implementation Method 1
DAS systems utilize Rayleigh backscatter of laser light energy to spatially detect deformation (often referred to as strains) that is distributed along the optical fibers
Implementation Method 2
The backscattered light is processed by a DAS system to determine light phase differences caused by strain and changes in strain along the fiber's core
Data Source
AI summary
Embodiments disclosed herein include components, devices, systems, and operations and functions for generating a seismic profile. An optical signal is generated in an optical signal medium disposed in proximity to a formation. A seismic source induces seismic signals within the formation. A backscatter response corresponding to the seismic signals from the optical signal medium is detected and quadrature modulated to generate a quadrature trace. A seismic response is generated by determining phase differences in the backscatter response based on the quadrature modulated backscatter response. Portions of the seismic response above or below a response threshold are removed to generate a threshold seismic response. The threshold seismic response is correlated with at least one of the seismic signals to generate a correlated seismic response.