Drillstring Stretch Correction Using Formation Image Continuity
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Solution Overview
Problem
Discrepancies in drillstring length measurements lead to misalignments in data logs during drilling operations, as existing methods fail to accurately account for drillstring stretch and depth variations, affecting the accuracy of downhole measurements.
Innovation Solution
A method involving a formation evaluation sensor that makes measurements with both compressional and reduced loads on the drillstring, estimating drillstring stretch by analyzing changes in image continuity, allowing for precise determination of drillbit contact with the borehole bottom and correcting for depth discrepancies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the drillstring is assumed to be inelastic and does not stretch, then the depth measurement process is simplified, but depth measurement accuracy deteriorates due to discrepancies between surface-estimated depth and actual borehole depth
Solution Approach 1:
The patent employs feedback by continuously monitoring image continuity features and using them to detect drillstring stretch events. The system feeds back depth correction information based on detected stretch events, adjusting the depth estimation to maintain accuracy despite drillstring elasticity. This closed-loop approach resolves the contradiction by adding intelligence to the measurement process rather than simply assuming inelasticity.
Solution Approach 2:
The patent changes the parameter being measured from raw depth to corrected depth by detecting changes in image continuity. When discontinuities are detected in formation features across successive images, the system infers drillstring stretch and applies corrections. This parameter transformation allows accurate depth measurement while accounting for elastic deformation without requiring complex real-time stress modeling.
2Measurement precision
If depth corrections are applied based on drillstring stress, then depth measurement accuracy is improved, but the measurement and correction process becomes more complex
Solution Approach 1:
The patent uses image continuity features as an intermediary to indirectly measure drillstring stretch. Instead of directly measuring stress or strain, the system uses formation images as a proxy - when the drillstring stretches, formation features appear discontinuous in the images. This intermediary approach simplifies the correction process by using easily observable image data rather than complex stress calculations.
Solution Approach 2:
The patent replaces direct mechanical stress measurement with image-based detection. Instead of using strain gauges or stress sensors on the drillstring, the system substitutes a mechanical measurement system with an optical/image analysis system. This substitution reduces measurement complexity while maintaining accuracy, as image analysis is computationally simpler than direct stress monitoring.
3Loss of information
If multiple sensors with different resolutions are used, then more comprehensive measurements are obtained, but depth correlation and vertical resolution matching become more difficult
Solution Approach 1:
The patent applies universality by using the same image continuity analysis method for all sensors and measurement types. The image-based depth correction system serves as a universal reference that can be applied regardless of which specific sensor is being used or what parameter is being measured. This multi-functional approach simplifies depth correlation across multiple sensors by providing a common correction framework.
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 accurate estimation of drillstring stretch and depth variations, improving the alignment of data logs and enhancing the accuracy of downhole measurements, thereby correcting for misalignments and improving drilling operations.
Implementation Method 1
making measurements with a formation evaluation (FE) sensor... producing an image of the formation using the measurements
Data Source
AI summary
Borehole images obtained with MWD measurements have a mismatch with subsequent images obtained when measurements are repeated over the same depth interval after the drillstring has been raised up. The difference is attributable to stretch of the drillstring. This can be estimated by correlating the two images. The difference can also be estimated by monitoring drilling conditions such as RPM, WOB and torque on reentry.