Optic Fiber Leak Detection in Well Casings
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Solution Overview
Problem
Existing methods for monitoring the integrity of well casings, particularly in production and injection wells, are inadequate for detecting leaks effectively, especially before cementing, due to limitations in existing distributed acoustic sensing technologies.
Innovation Solution
A method involving the deployment of optic fibers along the well casing, creation of a pressure differential, and distributed acoustic sensing to detect acoustic signals indicative of leaks, with additional steps to validate signals and account for systematic errors using multiple fibers and fiber movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If distributed acoustic sensing is used to detect leaks in well casings, then leak detection capability is improved, but systematic errors and false signals increase
Solution Approach 1:
The patent applies local quality by making different sections of the optical fiber serve different functions: some sections are stationary and buried in cement for stable baseline measurements, while other sections are moved to detect leaks. This differentiation allows the system to distinguish between systematic errors (detected by stationary fibers) and genuine leak signals (detected by moved fibers), thereby improving both reliability and measurement precision simultaneously
Solution Approach 2:
The patent implements preliminary action by performing multiple iterations of the leak detection process, moving the optical fiber to different positions and comparing signals across iterations. This preliminary repeated measurement allows the system to identify and filter out systematic errors before final leak detection, improving signal accuracy while maintaining reliable leak detection capability
2Measurement precision
If multiple optical fibers are deployed for signal validation, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the optical fiber system to serve multiple functions: the same optical fiber is used both as a sensing element and as a reference element across different iterations. By moving the fiber to different positions and reusing it for multiple measurements, the system achieves signal validation without requiring separate dedicated reference fibers, thus improving measurement precision while limiting the increase in device complexity
3Reliability
If pre-cementing leak detection is performed, then well integrity reliability is improved, but time required for well completion increases
Solution Approach 1:
The patent implements preliminary action by performing leak detection before cementing the well casing, allowing any integrity issues to be identified and addressed while the well is still accessible. This early detection prevents the need for time-consuming remediation after cementing, thereby improving well integrity reliability while actually reducing total well completion time by avoiding rework
Solution Approach 2:
The patent applies skipping by rapidly performing the leak detection measurement and iteration process before cementing, using efficient optical fiber deployment and quick signal analysis. This rapid assessment allows the system to obtain reliable integrity data without significantly extending the well completion schedule, thus improving reliability while minimizing time loss
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 allows for reliable pre-cementing leak detection in well casings, reducing the risk of environmental and economic consequences by ensuring well integrity before cementing, and enabling multiple iterations for accurate signal validation.
Implementation Method 1
interrogating the optic fibre to provide a distributed acoustic sensor
Implementation Method 2
providing a pressure differential between a fluid in the conduit and a fluid external to the conduit
Data Source
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Figure 3
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AI summary
The present invention relates to a method of integrity monitoring of a conduit. An optic fibre is provided optic fibre along the path of the conduit, and a fluid in the conduit is pressurized and depressurized. The optic fibre is interrogated to provide a distributed acoustic sensor, and data is sampled from a plurality of longitudinal portions of the fibre during the pressurizing and depressurizing. The data is processed to detect a signal characteristic of the integrity of the conduit.