Single-Photon Detector Interrogation for Subsea DAS Signal Integrity
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Solution Overview
Problem
Subsea operations face challenges in maintaining signal quality and noise ratio for Distributed Acoustic Sensing (DAS) systems due to long fiber lengths, leading to decreased pulse power and increased noise, which affects the accuracy of measurements in subsea environments.
Innovation Solution
The implementation of remote circulators and Raman amplification, along with optimized sampling frequencies and the use of single photon detectors, enhances signal strength, maintains pulse power, and reduces noise, thereby improving the signal-to-noise ratio and extending the effective length of fiber optic cables in subsea DAS systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If long fiber lengths are used in subsea DAS systems, then the sensing range is extended, but the signal-to-noise ratio deteriorates due to accumulated optical losses
Solution Approach 1:
Raman amplification is introduced as an intermediary mechanism to compensate for optical losses in long fiber lengths. The Raman pump laser provides distributed amplification along the fiber, acting as a mediator that maintains signal strength over extended distances without requiring discrete amplifier stations, thus preserving measurement precision while extending sensing range.
Solution Approach 2:
The system changes the optical parameters by using Raman pumping at specific wavelengths to stimulate Raman scattering, which transfers energy from the pump laser to the signal light. This parameter change enables distributed amplification along the fiber, compensating for losses and maintaining signal-to-noise ratio over long distances.
2Measurement precision
If conventional photodetectors are used, then the system complexity is lower, but the detection sensitivity and signal-to-noise ratio are insufficient for long fiber lengths
Solution Approach 1:
The patent replaces conventional photodetectors with single-photon detectors, substituting a more sensitive detection mechanism. Single-photon detectors can detect individual photons, providing significantly higher detection sensitivity and signal-to-noise ratio compared to conventional detectors, enabling reliable measurement over long fiber lengths despite the increased device complexity.
Data Source
AI summary
A distributed acoustic system may comprise an interrogator which includes a single photon detector, an umbilical line comprising a first fiber optic cable and a second fiber optic cable attached at one end to the interrogator, and a downhole fiber attached to the umbilical line at the end opposite the interrogator. A method for optimizing a sampling frequency may comprise identifying a length of a fiber optic cable connected to an interrogator, identifying one or more regions on the fiber optic cable in which a backscatter is received, and optimizing a sampling frequency of a distributed acoustic system by identifying a minimum time interval that is between an emission of a light pulse such that at no point in time the backscatter arrives back at the interrogator that corresponds to more than one spatial location along a sensing portion of the fiber optic cable.