NMR Logging Antenna Array for High Resolution
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Solution Overview
Problem
Existing NMR logging tools face a tradeoff between vertical resolution and signal-to-noise ratio (SNR), failing to provide high resolution and high SNR simultaneously due to limitations in magnetic field homogeneity and antenna configuration.
Innovation Solution
The use of an array of antennas with a static magnetic field and radio frequency field generation, combined with motion sensing to track and associate individual responses with specific positions, allowing for improved resolution without sacrificing SNR through signal stacking and exclusion of degraded measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single antenna is used in existing NMR logging tools, then the device complexity is low, but the vertical resolution and signal-to-noise ratio cannot be improved simultaneously
Solution Approach 1:
The patent divides the antenna system into multiple discrete antenna elements arranged in an array along the tool axis. Each antenna element can be independently controlled to transmit or receive NMR signals from specific depth intervals, enabling selective measurement of different formation zones and improving vertical resolution without requiring a single complex antenna
2Reliability
If the measurement volume is increased to improve signal-to-noise ratio, then the SNR improves, but the vertical resolution deteriorates
Solution Approach 1:
The antenna array enables segmentation of the measurement volume into discrete depth intervals, where each antenna element measures a specific zone. This allows the tool to accumulate signals from multiple antenna elements measuring the same formation zone (improving SNR) while maintaining the ability to resolve fine vertical features through selective antenna activation and signal processing
Solution Approach 2:
The patent combines signals from multiple antenna elements through coherent stacking and signal processing techniques. By merging measurements from multiple antennas that probe the same formation interval, the signal-to-noise ratio is improved while the vertical resolution is preserved through proper phase alignment and depth positioning of each antenna element
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 vertical resolution of NMR logging while maintaining a high signal-to-noise ratio, enabling more accurate measurements of formation properties like porosity and hydrocarbon saturation.
Implementation Method 1
nuclear magnetic resonance (NMR) logging tool. NMR tools operate by using an imposed static magnetic field, B0, to give nuclei with non-zero nuclear spin (non-zero angular momentum) split energy levels. Since lower energy levels are preferred, an ensemble of nuclei will exhibit an anisotropic distribution of energy states, giving the nuclear spins a preferential polarization parallel to the imposed field.
Implementation Method 2
During or after the polarization period, the tool applies a perturbing field, usually in the form of a radio frequency electromagnetic pulse whose magnetic component, B1, is perpendicular to the static field B0. This perturbing field moves the orientation of the magnetization into the transverse (perpendicular) plane.
Implementation Method 3
The polarized nuclei are perturbed simultaneously and, when the perturbation ends, they precess around the static magnetic field gradually re-polarizing to align with the static field once again while losing coherence in the transverse plane (T2 relaxation). The precessing nuclei generate a detectable radio frequency signal
Data Source
AI summary
Various disclosed nuclear magnetic resonance (NMR) logging systems and methods employ an array of antennas to provide increased resolution without sacrificing signal-to-noise ratio. Certain method embodiments include: establishing a static magnetic field (B0) with a tool moving along a borehole through a formation; concurrently driving a multiple antenna cells to produce a radio frequency field (B1) in said formation; measuring an individual response from each antenna cell as nuclear spins undergo precession in the formation; and determining at least one characteristic relaxation time of the formation based at least in part on the individual response. The individual responses can be associated with positions where the individual responses were measured, and the relaxation time can be determined from a combination of those responses associated with a given position. Certain responses may be excluded due to tool motion that degrades the measured response.