Fracture Aperture Calculation with Uncertainty Correction
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Solution Overview
Problem
Existing methods for determining fracture aperture in wellbores are limited by assumptions that may not always hold, leading to varying confidence levels in calculated outputs due to factors like fracture orientation, length, fluid fill, and background resistivity uncertainties.
Innovation Solution
A method involving downhole resistivity measurements, fracture detection, and calculation using a predetermined model with corrections for hypotheses not met, determining an uncertainty range for fracture aperture based on measured parameters and corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the Luthi-Souhaité equation is used to calculate fracture aperture, then the calculation is simple and widely applicable, but the confidence level varies due to multiple hypotheses that may not be met
Solution Approach 1:
The patent segments the uncertainty analysis into multiple independent hypothesis evaluations (fracture orientation, fluid fill, background resistivity, etc.). Each hypothesis is assessed separately and assigned a weight, allowing the overall confidence level to be calculated as a composite of individual hypothesis confidences. This segmentation enables systematic handling of multiple sources of uncertainty while maintaining calculation simplicity.
Solution Approach 2:
The patent introduces new parameters including confidence level (0-1 scale), hypothesis weights, and uncertainty metrics. These parameters transform the qualitative assessment of hypothesis validity into quantitative confidence levels, enabling more reliable interpretation of fracture aperture calculations without complicating the core Luthi-Souhaité equation.
2Reliability
If multiple hypotheses are assumed for the predetermined model, then the model is more comprehensive, but the complexity of evaluating and correcting for unmet hypotheses increases
Solution Approach 1:
The patent implements a tiered approach where not all hypotheses require full evaluation. A confidence level threshold system allows the methodology to focus computational resources on the most critical unmet hypotheses. When confidence exceeds the threshold, comprehensive evaluation is performed; when below, simplified corrections are applied, reducing overall complexity while maintaining reliability.
Solution Approach 2:
The patent establishes a feedback loop where the calculated confidence level feeds back into the model selection process. High confidence results use the base Luthi-Souhaité equation, while lower confidence results trigger hypothesis evaluation and correction procedures. This feedback mechanism dynamically adjusts the level of analysis based on result reliability, optimizing the balance between comprehensiveness and complexity.
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
Enhances the reliability of fracture aperture data by accounting for uncertainties, allowing for more accurate analysis and decision-making in wellbore operations.
Implementation Method 1
Measuring resistivity with a downhole tool in a wellbore for obtaining an image of the wellbore
Implementation Method 2
In the case of open fractures, and a normal overbalanced drilling condition with water base mud, the fractures appear conductive. The excess conductivity (or more correctly excess current flow) relative to the background response has a close relationship with the aperture of the fracture
Data Source
AI summary
A method for determining a fracture aperture of a fracture aperture in a wellbore comprises measuring a resistivity of the wellbore with a downhole tool in a wellbore for obtaining an image of the wellbore. Based on the image, the method detects fractures in the wellbore, and calculates a fracture aperture of the detected fracture according to a predetermined model of the wellbore set up based on hypothesis relative to the configuration of the wellbore. Then, the method estimates a correction to the predetermined model when at least one of the hypothesis is not met, and determines an uncertainty range for the fracture aperture also using a measured parameter.