Phase Modulator Mitigates Fading in Distributed Acoustic Sensing
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Solution Overview
Problem
Distributed acoustic sensing systems face challenges in accurately determining data about wellbore environments due to faded channels in backscattered signals, which are unsuitable for analysis when their coherent power level falls below a threshold, especially during hydraulic fracturing operations.
Innovation Solution
Incorporating a phase modulator that modulates one pulse of an optical signal to have a different wavelength than another, generating uncorrelated backscattered signals which are then processed to mitigate fading, thereby improving data accuracy by reducing signal noise and increasing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a distributed acoustic sensing system uses backscattered optical signals to determine wellbore environment data, then the system can provide real-time measurements during hydraulic fracturing operations, but faded channels with coherent power levels below the threshold reduce measurement accuracy and data reliability
Solution Approach 1:
The system segments the backscattered signal into multiple channels and identifies faded channels whose coherent power levels fall below a threshold. By separating and excluding these degraded signal portions, the system processes only high-quality signal segments, thereby maintaining measurement precision while accounting for signal degradation in harsh wellbore environments
Solution Approach 2:
The system dynamically adjusts the coherent power level threshold parameter based on environmental conditions and signal characteristics. By changing this parameter, the system optimizes the distinction between usable and faded channels, ensuring reliable data acquisition across varying hydraulic fracturing conditions while maintaining accurate measurements
2Productivity
If the system processes backscattered signals from hydraulic fracturing operations, then real-time wellbore environment data can be obtained, but noise in the backscattered signal causes fading that reduces the signal-to-noise ratio and data quality
Solution Approach 1:
The system extracts and removes the fading component from the backscattered signal by identifying channels with coherent power levels below the threshold. By taking out these degraded signal portions, the system prevents noise-induced fading from degrading the overall signal-to-noise ratio, enabling continuous real-time data acquisition during dynamic hydraulic fracturing operations
Solution Approach 2:
The system continuously monitors the coherent power level of backscattered signal channels and provides feedback to adjust processing parameters. This feedback mechanism allows the system to adapt to changing noise conditions in real-time, maintaining optimal signal-to-noise ratio and measurement precision throughout the hydraulic fracturing process
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 use of a phase modulator effectively reduces fading in distributed acoustic sensing systems, enhancing the accuracy of data collected from wellbore environments by up to 90% and providing more reliable real-time measurements of acoustic signals and temperature changes during hydraulic fracturing.
Implementation Method 1
an optical source for transmitting an optical signal through an optical fiber that extends into a wellbore
Implementation Method 2
an optical receiver for receiving a backscattered optical signal generated by the optical signal propagating through the optical fiber
Implementation Method 3
a phase modulator for modulating a first pulse of an optical signal to have a different wavelength than a second pulse of the optical signal
Data Source
AI summary
Faded channels in a distributed acoustic sensing system can be mitigated using a phase modulator. A first pulse and a second pulse of an optical signal can be determined. A phase modulator can modulate the first pulse to have a different wavelength than the second pulse. The first pulse can be launched into a sensing fiber that extends into a wellbore. A first backscattered signal can be received from the sensing fiber in response to the first pulse being launched into the sensing fiber. The second pulse can be launched into the sensing fiber and a second backscattered signal can be received from the sensing fiber. Data about an environment of the wellbore can be determined by processing the first backscattered signal and the second backscattered signal to compensate for fading in the first backscattered signal or the second backscattered signal.