Distributed Vibration Sensing Calibration via Temperature Gradients
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Solution Overview
Problem
Distributed fiber optic sensors face challenges in linking channel data to physical locations, such as depth in a wellbore, due to the difficulty in determining reliable reference points, which hinders the generation of a calibrated depth scale for accurate seismic and fluid flow monitoring.
Innovation Solution
A channel-depth calibration system is employed using a localized calibration source, such as a temperature or vibration source, to generate a calibration scale by identifying reference points through processing backscattered light, allowing for the determination of specific locations along the optical fiber and thus calibrating the depth of acoustic events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If distributed fiber optic sensors are deployed to monitor acoustic events in wellbores, then the sensing coverage and monitoring capability are improved, but the ability to accurately link channel data to physical locations deteriorates due to difficulty in determining reliable reference points
Solution Approach 1:
The patent introduces an intermediary calibration process that uses environmental condition interfaces (such as temperature gradients between above and below wellhead regions) as mediator markers to establish reference points. These intermediary markers bridge the gap between the sensor channel data and physical depth locations, enabling accurate calibration without requiring direct physical access to all sensor points.
Solution Approach 2:
The patent utilizes changes in environmental parameters (temperature, vibration characteristics) at known physical locations to create detectable signatures that mark reference points. By monitoring parameter changes along the fiber optic sensor, the system can identify specific depth locations corresponding to channel data, thereby establishing the channel-depth calibration scale.
2Measurement precision
If reference points are determined to generate a channel-depth calibration scale, then the location identification precision is improved, but the system complexity and calibration process difficulty increase
Solution Approach 1:
The calibration system utilizes naturally occurring environmental condition interfaces (such as the temperature gradient at the wellhead interface) that exist in the field environment. These self-existing markers eliminate the need for complex artificial calibration devices or manual reference point establishment, allowing the system to calibrate itself using readily available environmental features.
Solution Approach 2:
The calibration methodology uses environmental condition interfaces that can serve multiple purposes: they mark reference points for calibration, provide information about wellhead location, and can indicate transitions between different wellbore zones. This multi-functionality reduces the need for separate calibration mechanisms and simplifies the overall system.
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 the generation of a reliable channel-depth calibration scale, allowing for precise location identification and accurate monitoring of acoustic events in wellbores, enhancing the effectiveness of distributed vibration sensing systems.
Implementation Method 1
a detector to detect backscattered light generated by the optical fiber in response to the launched optical signals
Implementation Method 2
The localized calibration event is a temperature change
Data Source
AI summary
A method for calibrating a distributed vibration sensing system includes applying a localized calibration event, such as a temperature change, to at least one location along an optical fiber cable. Backscattered light generated the optical fiber while the localized calibration event is applied includes phase information having low frequency components. The center of energy of the low frequency components can be identified in order to generate a reference point along the fiber that can be used to generate a channel-depth calibration scale that can be applied to vibration data acquired from the fiber when used in various applications, such as borehole seismic surveying.