Saddle-Point NMR Sensor Layout for Multi-Depth Logging
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Solution Overview
Problem
Current NMR logging tools face challenges in generating accurate data at multiple depths of investigation (DOI) due to sensitivity to magnetic debris and inability to maintain high signal-to-noise ratio (SNR) across varying geological formations.
Innovation Solution
The use of a magnet configuration with multiple magnets, where the magnetic fields of at least one magnet partially cancel out the magnetic field gradient of another, creating a saddle point sample region with zero gradient, allowing for multiple DOI measurements while minimizing interference from borehole signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a permanent magnet produces a static magnetic field for NMR measurements, then NMR data can be obtained at a single depth of investigation, but the tool cannot measure multiple DOIs and is sensitive to magnetic debris
Solution Approach 1:
The permanent magnet is divided into multiple magnet segments (first through fourth segments) arranged in a specific pattern around the borehole. Each segment produces a magnetic field component, and their combined effect creates a saddle point magnetic field configuration that enables multiple DOI measurements while maintaining measurement precision through geometric arrangement rather than using a single large magnet
Solution Approach 2:
The patent transitions from a single-depth measurement approach to multi-depth measurement by creating a three-dimensional magnetic field configuration with saddle points at different distances from the borehole. This dimensional approach allows simultaneous measurement at multiple DOIs by utilizing the radial and axial dimensions of the magnetic field geometry
2Measurement precision
If the magnetic field gradient is high to improve signal strength, then NMR signal strength increases, but borehole signal interference increases
Solution Approach 1:
The magnetic field configuration creates localized saddle points with specific gradient characteristics at different radial distances from the borehole. By positioning measurement zones at these localized saddle points where the field gradient is optimized, the system achieves high signal-to-noise ratio for formation measurements while the borehole region experiences different field characteristics that minimize its signal contribution
Solution Approach 2:
The patent utilizes the borehole signal that would normally be interference as a reference to enhance formation signal detection. The specific magnetic field configuration allows differentiation between borehole and formation signals, converting the previously harmful borehole signal into a useful reference for improving the signal-to-noise ratio of formation measurements
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 configuration enhances the signal-to-noise ratio and provides accurate NMR data at multiple depths, reducing interference from borehole signals and improving fluid invasion profile measurements.
Implementation Method 1
an arrangement of magnets producing a magnetic field having a gradient of magnetic field that is zero, or negligibly small, at a saddle point field location
Implementation Method 2
nuclear magnetic resonance (NMR) to measure the response of nuclear spins in formation fluids to applied magnetic fields
Data Source
Figure 1
Figure 2~3
Figure 4~5A
AI summary
The present disclosure relates to generating multiple depths of investigation (DOI) measurements with a saddle point design nuclear magnetic resonance sensor. In general, an NMR sensor in accordance with the present disclosure includes a first magnet at a first radial distance from a radial center, and a second magnet at a second radial distance from the radial center. The first magnet at least partially cancels out a magnetic field gradient produced by the second magnet. Further, the NMR sensor may include an antenna that generates a first set of NMR data from a first DOI by operating at a first frequency and, generates a second set of NMR data from a second DOI by operating a second frequency. Additional frequencies are possible and envisioned.