Fiber Optic Pressure Sensors for Flexible Riser Annulus Water Detection
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Solution Overview
Problem
Current methods for detecting liquid presence in the annulus of flexible risers in subsea systems are inaccurate and difficult to control, particularly in low-lying areas, leading to potential catastrophic failures due to corrosion and pressure increases, with existing solutions failing to reliably identify small water intrusions or leaks.
Innovation Solution
A system utilizing fiber optic pressure sensors embedded in open-ended tubes within the annulus, allowing for real-time measurement of pressure and temperature changes, enabling accurate detection of water ingress and leak locations through optical interrogation, eliminating the need for electrical connections and simplifying the monitoring process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If periodic monitoring of vented gas flow rate and vacuum testing are used to detect liquid presence, then the monitoring process is simple, but the detection accuracy is low and small water intrusions are difficult to detect
Solution Approach 1:
The patent replaces mechanical/electrical pressure sensing systems with fiber optic pressure sensors that use optical principles. The fiber optic sensors measure pressure changes in the annulus caused by water accumulation, eliminating the need for electrical connections in the harsh subsea environment while providing high-resolution detection capability.
Solution Approach 2:
The patent introduces fiber optic cables as an intermediary medium to transmit pressure information from the annulus to the surface for analysis. The optical fiber acts as a mediator that carries measurement data without requiring electrical power or signal transmission through the corrosive environment, enabling accurate remote monitoring.
2Measurement precision
If fiber optic pressure sensors are used for real-time pressure measurement, then detection accuracy improves, but device complexity increases
Solution Approach 1:
The fiber optic pressure sensors are designed to be self-contained and self-powered, utilizing the existing optical infrastructure for both signal transmission and power delivery. The system leverages the natural properties of optical fibers to provide autonomous operation without requiring additional electrical infrastructure or complex control systems.
Solution Approach 2:
The fiber optic cable serves multiple functions simultaneously: it acts as the structural reinforcement element in the annulus, the pressure sensing medium, and the data transmission conduit. This multi-functionality reduces overall system complexity by eliminating separate components for each function.
3Reliability
If open-ended tubes with fiber optic sensors are installed in the annulus, then water ingress detection capability improves, but installation complexity increases
Solution Approach 1:
The fiber optic pressure sensors and open-ended tubes are pre-installed and integrated into the flexible riser structure during the manufacturing process, before the riser is deployed to the subsea location. This preliminary installation ensures proper positioning and sealing, reducing installation complexity during the actual deployment while maintaining high detection reliability.
Solution Approach 2:
The fiber optic sensor is nested within the open-ended tube, which itself is positioned within the annulus of the flexible riser. This nested configuration allows the sensing element to be protected and properly positioned without requiring separate mounting structures, simplifying the overall installation process.
Data Source
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AI summary
A method, device, and system for determining whether liquid enters a subsea system includes a flow line having an inside bore capable of carrying producing fluids from a subsea wellhead to a floating production storage and offloading vessel (FPSO). An annulus is defined between an innermost sheath that surrounds the inside bore and an outermost sheath at an exterior of the flow line. The device further includes a housing element disposed within the annulus and in hydraulic communication with the annulus; a sensor element disposed at a pre¬ determined location within the housing element; and data acquisition equipment capable of: determining environmental characteristics of the annulus based on measurements made by the sensor element, and determining at least one of the presence, location, and rate of collection of liquids in the subsea system based on the environmental characteristics of the annulus.