Side-Looking NMR Tool with Tilted Magnets
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Solution Overview
Problem
Current NMR well logging tools face limitations in achieving high signal-to-noise ratio (SNR) and maximum depth of investigation (DOI) due to the conventional perpendicular orientation of magnetic fields, which also results in higher power consumption and increased borehole signal density.
Innovation Solution
A side-looking NMR tool design featuring a pair of permanent magnets with non-parallel magnetization angles, optimized through a tilt angle between 75° and 105°, combined with a high conductivity screen and magnetically permeable antenna cores, shapes the RF magnetic field to enhance SNR and gradients while reducing power consumption and borehole signal density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional perpendicular orientation of magnetic fields is used, then NMR measurement can be performed, but signal-to-noise ratio is limited and depth of investigation is reduced
Solution Approach 1:
The patent applies asymmetry by using two permanent magnets with non-parallel magnetization directions (tilted at different angles relative to the tool axis) instead of the conventional symmetric perpendicular orientation. This asymmetric configuration creates an optimized magnetic field distribution that enhances the signal-to-noise ratio and increases the depth of investigation while maintaining measurement functionality.
2Use of energy by moving object
If conventional perpendicular magnetic field orientation is used, then NMR signal can be generated, but power consumption increases
Solution Approach 1:
The patent changes the parameter of magnetic field orientation from the conventional perpendicular configuration to a tilted non-parallel arrangement. This parameter change optimizes the magnetic field distribution to better align with the formation characteristics, thereby reducing power consumption while maintaining or improving NMR signal generation efficiency.
3Measurement precision
If conventional magnetic field orientation is used, then measurement can be conducted, but borehole signal density increases
Solution Approach 1:
The asymmetric tilted magnet configuration creates a magnetic field distribution that is optimized for formation measurement while minimizing interference from borehole signals. The non-parallel magnetization directions create field patterns that reduce the density of unwanted borehole signals, thereby improving the accuracy of formation information measurement.
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
The novel design improves SNR, increases gradient span, reduces power consumption, and diminishes unwanted borehole signals, leading to more accurate formation information and efficient NMR data acquisition.
Implementation Method 1
the intensity of the NMR signal is proportional to the amount of hydrogen present in the sample. By calibrating the intensity of the resulting NMR signal to the signal intensity of known fluids, the porosity, permeability and movable fluid characterization of the system can be found.
Implementation Method 2
An assembly of magnetic moments such as those of hydrogen nuclei will act like tiny bar magnets and will align along the direction of an applied magnetic field B0 thus resulting in bulk magnetization of the affected hydrogen protons.
Implementation Method 3
Numar Corporation developed the first commercial pulsed NMR tool that included permanent, prepolarizing magnets and utilized radio frequency ('RF') pulses to manipulate the magnetic properties of hydrogen nuclei in formation fluids.
Implementation Method 4
The sensor may include an RF antenna that includes an RF frame antenna and a pair of magnetically permeable antenna cores and the sensor further includes a high conductivity screen disposed between the permanent magnets and the pair of magnetically antenna cores such that RF magnetic fields generated by the sensor are shaped by the combined action of the magnetically permeable antenna cores and the high conductivity screen.
Data Source
AI summary
Apparatus and methods are described for a side looking NMR tool for downhole geophysical analysis wherein a unique static field shape is provided by two magnets magnetized in two different directions. The tilted configuration of magnets and optimized value of the tilt angle provide, among other advantages, an elevation of the Signal-to-Noise-Ratio (SNR), an enriched content of the 1H NMR signal from rock formations by providing a wider span of gradients including higher gradients, a diminished level of undesired sodium 23Na signal, less tool energy consumption and a wider NMR beam.