Fiber Optic Acoustic Sensor for Cement Sheath Location
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Solution Overview
Problem
Existing methods for detecting acoustic waves in downhole applications are intrusive, time-consuming, and require prior knowledge of well properties, limiting their effectiveness in hydrocarbon production and other fluid monitoring applications.
Innovation Solution
A distributed acoustic sensor system using fiber optics is deployed along elongate structures to directly measure acoustic wave velocity and attenuation as a function of position, allowing for real-time monitoring of fluid properties and formation characteristics by tracking guided acoustic waves and analyzing coherent Rayleigh backscatter signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional acoustic logging with hydrophones is used, then acoustic wave detection is achieved, but the method is intrusive and extremely time-consuming
Solution Approach 1:
The patent replaces the mechanical hydrophone-based acoustic logging system with an optical sensing system using fiber optic cables. The fiber optic cable detects acoustic waves through optical interference patterns (such as Fabry-Perot resonances) that change in response to acoustic pressure, eliminating the need for mechanical hydrophones and significantly reducing measurement time while maintaining detection capability.
2Loss of information
If pressure pulses are launched from surface to detect obstructions, then information about wellbore obstructions is obtained, but prior knowledge of fluid properties and wave velocity calibration is required
Solution Approach 1:
The fiber optic acoustic sensing system performs self-calibration by directly measuring acoustic wave propagation characteristics along the wellbore. The system uses the fiber optic cable itself as both the sensor and the reference medium, detecting acoustic waves transmitted through the wellbore fluid and casing without requiring external calibration data or prior knowledge of fluid properties. The optical interference patterns provide direct measurements of acoustic velocity and obstruction locations.
3Productivity
If fiber optic cable is used to detect acoustic waves, then non-invasive real-time monitoring is achieved, but the system complexity increases
Solution Approach 1:
The fiber optic cable serves multiple functions simultaneously: it acts as the acoustic sensor, the signal transmission medium, and the structural element for deploying the sensing system along the wellbore. This multi-functionality reduces overall system complexity compared to using separate components for each function, while enabling non-invasive real-time monitoring of acoustic waves for wellbore characterization.
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 enables non-invasive, efficient monitoring of fluid properties and formation characteristics, improving the accuracy and speed of data collection while reducing the need for prior calibration, enhancing hydrocarbon production optimization and other fluid-related applications.
Implementation Method 1
tracking propagation of the guided acoustic wave along the elongate structure based on the detected coherent Rayleigh backscatter signals
Data Source
AI summary
A distributed acoustic wave detection system and method is provided. The system may include a fiber optic cable deployed in a well and configured to react to pressure changes resulting from a propagating acoustic wave and an optical source configured to launch interrogating pulses into the fiber optic cable. In addition, the system may include a receiver configured to detect coherent Rayleigh noise produced in response to the interrogating pulses. The CRN signal may be used to track the propagation of the acoustic waves in the well. Such capability allows the location of the cement sheath, as well as measuring the bonding of cement to at least a casing string at least partially surrounded by a cement sheath.