Fiber Optic Shape Sensing with Anchoring Points
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Solution Overview
Problem
Existing shape sensing systems for downhole structures, such as boreholes, face challenges in accurately monitoring the dynamic shape and relative position due to factors like twisting and localized effects, which can affect the reliability of measurements, especially for inaccessible structures.
Innovation Solution
A shape sensing system employing optical fibers with fiber Bragg gratings and a tunable laser, combined with attachment points for enhanced accuracy, processes interferometric data to estimate the shape of tubular structures by integrating error corrections from known attachment points, addressing torsional effects and improving measurement reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fiber optic cables are embedded or attached to monitor dynamic shape, then shape information can be obtained independently from temperature or load effects, but localized effects such as twisting can affect measurement reliability
Solution Approach 1:
The system segments the continuous fiber optic cable into discrete measurement sections by identifying attachment points where the cable is secured to the structure. These attachment points serve as reference segments that anchor the shape calculation, dividing the measurement problem into manageable sections that can be independently validated against known positional relationships.
Solution Approach 2:
The system uses feedback from known attachment point locations to continuously validate and correct shape measurements. By comparing measured positions of attachment points against their known fixed positions, the system can detect and compensate for cumulative errors, maintaining measurement reliability over the entire length of the structure.
2Loss of information
If the shape of the structure is calculated by comparing the measured waveform and an earlier zero-strain waveform, then shape information can be extracted, but localized effects such as twisting are not accounted for
Solution Approach 1:
The system performs preliminary identification and recording of attachment point locations along the fiber optic cable before shape measurements are taken. These pre-established reference points serve as known constraints that are incorporated into the shape calculation algorithm, allowing the system to distinguish between actual shape changes and measurement artifacts from localized effects like twisting.
3Ease of operation
If fiber optic cables are used to monitor inaccessible structures such as boreholes, then downhole information can be obtained, but the reliability of shape information is crucial and may be compromised by measurement limitations
Solution Approach 1:
The system uses attachment points as intermediary reference elements that mediate between the fiber optic measurements and the actual structure shape. These attachment points serve as known intermediaries whose fixed positions provide a reliable reference framework, allowing accurate shape reconstruction even in the challenging downhole environment where direct observation is impossible.
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
The system provides more accurate strain and shape measurements by compensating for torsional effects, enhancing the reliability of downhole operations and maintenance through precise data interpretation and error correction.
Implementation Method 1
Information pertaining to the shape of the structure is manifest in the phase of radiation propagating within the fiber and is therefore extractable using interferometric techniques
Implementation Method 2
one or more optical fibers coupled to the tubular at a one or more attachment points
Implementation Method 3
A shape sensing system employing optical fibers with fiber Bragg gratings
Data Source
Figure 1
AI summary
Disclosed herein is a method for sensing one or more selected parameters related to a structure of interest, for example, the shape of an isolated structure. A cable is attached to the structure of interest at one or more attachment points. The cable contains one or more optical fibers. One or more light signals are transmitted into the one or more optical fibers and then detected to form a data set. The data set is compared with information known about the one or more attachment points to determine error values. The error values are then combined with the data set to determine the selected parameters associated with the structure.