Resistivity Logging Tool Ferrites with Non-Magnetic Dividers
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Solution Overview
Problem
Molded ferrites used in wellbore logging tools often exhibit non-homogeneous permeability due to the molding process, leading to variations in magnetic field roundness and symmetry, which affects the accuracy of measurements.
Innovation Solution
The use of a high length-to-width aspect ratio for ferrites and non-magnetic dividers between adjacent ferrites to prevent a continuous magnetic path, along with air-gapping or laminations, to control and compensate for permeability variations and enhance magnetic field directionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If ferrites are molded into desired geometric shapes using powder mixing and pressing, then complex geometries can be achieved, but non-homogeneous permeability and large variance in relative permeability occur
Solution Approach 1:
The patent divides the ferrite structure into multiple discrete elements or segments arranged in specific patterns. This segmentation allows each element to be manufactured with more consistent properties while the collective arrangement achieves the desired geometric function, reducing the impact of local non-homogeneities on overall performance
Solution Approach 2:
The patent employs different ferrite material properties or compositions in different regions of the structure. By tailoring the local permeability characteristics to specific functional requirements, the design compensates for molding non-homogeneity and optimizes the magnetic field distribution in critical areas
2Ease of manufacture
If ferrites are molded from powder mixtures, then manufacturing complexity is reduced, but field roundness and symmetry are adversely affected
Solution Approach 1:
The patent deliberately introduces asymmetric features or intentional non-uniformities in the ferrite structure that compensate for the random non-homogeneity from molding. These controlled asymmetric elements help restore field symmetry by counterbalancing the random deviations in permeability distribution
Solution Approach 2:
The patent incorporates design features that pre-compensate for expected molding non-homogeneity. By anticipating the direction and magnitude of permeability variations during the design phase, the structure is configured to produce the desired field characteristics despite manufacturing variations
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 ensures a more uniform and controlled magnetic field, improving the accuracy and consistency of measurements taken by wellbore logging tools, even with non-homogeneous ferrites, by minimizing the impact of permeability variance on the magnetic field direction and distribution.
Implementation Method 1
The ferrites facilitate a higher magnetic permeability path (i.e., a flux conduit) for the magnetic field generated by the coil windings
Implementation Method 2
help shield the coil windings from the drill collar and associated losses (e.g., eddy currents generated on the drill collar)
Data Source
AI summary
A method of fabricating a ferrite for use in a resistivity logging tool includes providing an uncured ferrite material, and pressing the uncured ferrite material into a channel to form the ferrite. The channel is defined on a surface of a bobbin associated with the resistivity logging tool, and the channel can be arcuate and extend at an angle offset from a central axis of the bobbin. The uncured ferrite material is then cured in place within the channels on the bobbin.