Downhole Logging Tool Anisotropic Resistivity Measurement
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Solution Overview
Problem
Existing resistivity logging tools face challenges in accurately measuring anisotropic resistivity in subsurface formations, particularly in harsh drilling environments, and require individual antenna calibration, which is cumbersome and sensitive to changes in coil configurations.
Innovation Solution
A downhole logging tool with a combination of transverse, tilted, and axial antennas that measures transverse-to-tilted and tilted-to-axial couplings, allowing for improved sensitivity to anisotropy and vertical response without the need for individual antenna calibration, using specific ratios that are insensitive to coil calibration changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transverse-to-tilted coupling measurements are used for small dip angles, then sensitivity to anisotropy is achieved, but vertical response is insufficient and individual antenna calibration is required
Solution Approach 1:
The patent combines transverse-to-tilted coupling measurements with tilted-to-axial coupling measurements into a unified measurement system. This merging allows the system to achieve both sensitivity to anisotropy and improved vertical response while eliminating the need for individual antenna calibration, as the combined ratio measurement is insensitive to calibration changes
Solution Approach 2:
The tilted antennas serve multiple functions: they provide sensitivity to anisotropy through transverse-to-tilted coupling measurements, improve vertical response through tilted-to-axial coupling measurements, and enable calibration-free operation. This multi-functionality resolves the contradiction by making the measurement system universally applicable without requiring individual antenna calibration
2Measurement precision
If only transverse-to-tilted coupling measurements are used, then anisotropy sensitivity is obtained, but vertical response is limited
Solution Approach 1:
The patent merges transverse-to-tilted coupling measurements with tilted-to-axial coupling measurements to simultaneously achieve anisotropy sensitivity and vertical response. The combination of these two measurement types allows the system to capture both horizontal anisotropy information and vertical resistivity information without losing either type of data
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 enhances the sensitivity to anisotropic resistivity and vertical resistivity measurements, providing more accurate logs and easier calibration, while maintaining stability in harsh drilling conditions.
Implementation Method 1
A downhole logging tool has a plurality of spaced antennas, at least one of which is a transverse antenna, at least two of which are tilted antennas, and at least two of which are axial antennas. Measurements of the transverse-to-tilted, and tilted-to-axial couplings are obtained.
Data Source
AI summary
The present disclosure relates to a method to determine the vertical resistivity of a subsurface formation. A downhole logging tool having a plurality of spaced antennas, at least one of which is a transverse antenna, at least two of which are tilted antennas, and at least two of which are axial antennas is provided. Measurements involving the transverse and/or the tilted antennas of the downhole logging tool are obtained. Voltage ratios are formed using the measurements, and conditioning factors are formed by raising the determined voltage ratios not involving the transverse antenna to some arbitrary power. The sum of the exponents of the conditioning factors preferably equals one. A voltage ratio involving the transverse antenna is multiplied by the conditioning factors, and the vertical resistivity of the subsurface formation is determined using the resulting ratio.