Rotational Indexing for NMR Logging Magnet Uniformity
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Solution Overview
Problem
Nuclear magnetic resonance (NMR) logging tools face challenges due to inaccuracies in permanent magnet manufacturing, leading to deviations in magnetic field orientation, which affect the signal-to-noise ratio and sensitivity, especially in low gradient field approaches.
Innovation Solution
The method employs rotational indexing to optimize the sensing volume by establishing an initial magnet arrangement, measuring magnetic field properties, and rotating magnets to achieve uniformity and symmetry, securing them for improved performance in NMR logging tools for wireline, tubing-conveyed, and logging while drilling applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If permanent magnets are manufactured with standard tolerances, then manufacturing cost is reduced, but magnetic field uniformity and symmetry deteriorate
Solution Approach 1:
The patent applies preliminary action by measuring the magnetic field of each individual magnet before assembly and calculating the optimal rotational orientation for each magnet in advance. This pre-planning allows magnets with standard manufacturing tolerances to be positioned to compensate for their individual variations, achieving uniform field symmetry without requiring expensive tight-tolerance manufacturing
Solution Approach 2:
The patent changes the rotational orientation parameter of each magnet based on its measured field characteristics. By rotating each magnet to a specifically calculated angle, the system compensates for manufacturing variations and achieves optimal field uniformity and symmetry using off-the-shelf magnets with standard tolerances
2Manufacturing precision
If permanent magnets are manufactured with tight tolerances, then magnetic field uniformity is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the rotational orientation parameter of each magnet based on its measured field characteristics. By rotating each magnet to a specifically calculated angle, the system compensates for manufacturing variations and achieves optimal field uniformity and symmetry using off-the-shelf magnets with standard tolerances
Solution Approach 2:
The patent creates a digital model or map of each magnet's actual magnetic field characteristics through measurement. This 'copy' of the field data is then used to calculate the optimal positioning, allowing the system to work around manufacturing variations without requiring tighter physical tolerances
3Volume of stationary object
If low gradient field approach is used to increase sensing volume, then signal to noise ratio is improved, but sensitivity to field deviations increases
Solution Approach 1:
The patent applies preliminary action by measuring the magnetic field of each individual magnet before assembly and calculating the optimal rotational orientation for each magnet in advance. This pre-planning allows magnets with standard manufacturing tolerances to be positioned to compensate for their individual variations, achieving uniform field symmetry without requiring expensive tight-tolerance manufacturing
Solution Approach 2:
The patent changes the rotational orientation parameter of each magnet based on its measured field characteristics. By rotating each magnet to a specifically calculated angle, the system compensates for manufacturing variations and achieves optimal field uniformity and symmetry using off-the-shelf magnets with standard tolerances
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 uniformity and symmetry of the magnetic field, improving the signal-to-noise ratio and allowing for more accurate measurements of porosity, permeability, and fluid properties, while also relaxing manufacturing tolerances and reducing costs.
Implementation Method 1
an arrangement of permanent magnets to generate a static magnetic field in the formation around a borehole
Implementation Method 2
nuclear magnetic resonance (NMR) logging tool... NMR tools employ an arrangement of permanent magnets to establish a strong magnetic field in some designated sensing volume
Data Source
AI summary
A nuclear magnetic resonance (NMR) logging tool assembly method that employs rotational indexing to optimize the sensing volume. At least some embodiments include establishing an initial arrangement of the permanent magnets and marking each magnet to indicate their relative rotational orientations in the initial arrangement. Thereafter a series of magnetic field measurements and individual magnet rotations are performed to improve the uniformity of the magnetic field in the sensing volume. Once a satisfactory arrangement has been found, the magnets may be secured together and an antenna array installed along with the electronics for performing relaxation time measurements and providing logs of formation properties that can be derived therefrom, such as porosity, permeability, density, rock type, fluid type, etc. The tool may be packaged as a wireline sonde, a tubing-conveyed logging tool, or a logging while drilling (LWD) tool.