Segmented Resistivity Lookup for Faster Downhole Well Logging
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Solution Overview
Problem
Resistivity lookup and Lagrange interpolation in wellbore logging tools consume significant memory and processing cycles due to the need for storing data for every value of resistivity and performing complex interpolation calculations, which is impractical given the limited computational resources of downhole tools.
Innovation Solution
Implementing a segmented lookup table with polynomial coefficients for resistivity calculations, where data is grouped into segments and represented by low-order polynomials, reducing the need for interpolation and minimizing memory and processing requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complete lookup table with data for every resistivity value is used, then measurement precision is improved, but memory usage and device complexity increase significantly
Solution Approach 1:
The lookup table is divided into multiple segments, each covering a specific resistivity range. Instead of storing complete data for all possible resistivity values, the system stores segmented tables with representative data points. This segmentation allows the system to achieve accurate resistivity calculations within each segment while dramatically reducing the total memory required compared to a complete lookup table.
2Measurement precision
If Lagrange interpolation is used to calculate resistivity between table values, then measurement precision is improved, but processing time and computational resources increase
Solution Approach 1:
By segmenting the lookup table and storing pre-calculated representative data points for each segment, the system eliminates the need for complex Lagrange interpolation calculations. The segmented structure allows for direct or simplified calculations within each segment, dramatically reducing processing time while maintaining adequate precision for logging applications.
Solution Approach 2:
The system changes the approach from continuous interpolation to discrete segmented representation. By transforming the continuous resistivity scale into discrete segments with representative values, the system achieves a practical balance between precision and computational efficiency suitable for downhole processing constraints.
3Measurement precision
If downhole tools are designed with sufficient memory and processing power for complete lookup tables and interpolation, then measurement precision is improved, but device complexity and design constraints are worsened
Solution Approach 1:
The segmented lookup table approach allows downhole tools to achieve accurate resistivity measurements without requiring large memory capacities or high-speed processors. By dividing the data into manageable segments with representative points, the system reduces the computational burden and memory requirements, enabling implementation in resource-constrained downhole environments while maintaining measurement quality.
Data Source
AI summary
A method for well logging may comprise: inserting a downhole tool into a wellbore penetrating a subterranean formation wherein the downhole tool comprises: a transmitter; a receiver; a memory configured to store at least one look up table with polynomial coefficients; and a processor coupled to the memory; obtaining a measurement using the resistivity tool; and generating a resistivity output using the measurement as an input to a polynomial with polynomial coefficients sourced from the look up table.