Waveguide Tension Control for Downhole Strain Sensing
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Solution Overview
Problem
Optical fibers used in monitoring wells for micro-seismic and strain detection often break due to excessive tension or strain during deployment, leading to damage and interference with strain measurements in surrounding formations, which is costly and limits the effectiveness of subsurface sensing systems.
Innovation Solution
Implementing a system that actively monitors and controls fiber tension in real-time during and after deployment using sensors like strain gauges and Fiber Bragg Gratings, regulating pump rates to maintain optimal flow and minimize tension, and releasing additional fiber to reduce remnant tension, thereby preventing breakage and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If optical fiber is deployed in monitoring wells using gravity and fluid pumping, then the fiber can reach the wellbore for micro-seismic and strain detection, but excessive tension and strain during deployment cause fiber breakage and damage
Solution Approach 1:
The system performs preliminary actions by deploying the fiber optic cable completely into the wellbore before any tension-relief operations. The fiber is deployed through gravity and fluid pumping to the target location, ensuring full deployment is achieved first. Only after complete deployment does the system then release additional fiber to create slack and reduce tension, preventing breakage during subsequent operations.
Solution Approach 2:
The system changes the physical state of the fiber deployment by transitioning from a tensioned state during initial deployment to a slack state after deployment. This is achieved by releasing additional fiber length, which changes the tension parameter from high (during deployment) to low (after deployment with slack), thereby preventing fiber breakage while maintaining deployment effectiveness.
2Productivity
If pump rate is increased to propel the dart to the toe of the well, then deployment speed increases, but excessive tension is created in the optical fiber
Solution Approach 1:
The system allows the fiber to be deployed completely under pump force first, achieving the deployment goal. Only after the dart reaches the toe of the well does the system then release additional fiber to create slack, thereby retroactively reducing the tension that was necessary to achieve the deployment speed.
Solution Approach 2:
The system changes the tension parameter after deployment by releasing additional fiber length. This parameter change from high tension (during high-speed pumping) to low tension (after slack is introduced) resolves the contradiction by allowing high deployment speed during the deployment phase while maintaining low tension during the monitoring phase.
3Reliability
If additional fiber is released to create slack and reduce tension, then fiber breakage risk decreases, but the system complexity increases
Solution Approach 1:
The system uses the existing fiber optic cable itself to resolve the tension problem by releasing additional length of the same cable. This self-service approach creates slack to reduce tension without introducing entirely new components, thereby reducing system complexity while improving fiber durability.
4Measurement precision
If optical fiber tension is not minimized, then strain measurements in surrounding formations are interfered with by noise, but implementing tension monitoring and control increases system complexity
Solution Approach 1:
The fiber optic cable serves dual functions: it both senses strain in the formation and provides the mechanism for tension relief. By releasing additional fiber length, the system uses the sensing element itself to control tension, thereby improving measurement precision without proportionally increasing system complexity.
Solution Approach 2:
The fiber optic cable performs multiple functions: it serves as both the sensing element for strain measurement and as the mechanism for tension control. This multi-functionality allows the system to improve measurement precision while minimizing additional complexity, as the same component used for sensing also enables tension relief.
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 extends the service life of disposable waveguides, reduces the risk of fiber breakage, and enhances the precision of strain measurements by maintaining the waveguide at minimal tension, thus improving the detection of strain changes in the wellbore.
Implementation Method 1
detecting one or more properties of a waveguide having a downhole end and an uphole end
Data Source
AI summary
A method, includes: detecting one or more properties of a waveguide having a downhole end and an uphole end; and responsive to the detected one or more properties, positioning into a passage of a wellbore the waveguide to minimize tension thereof.