Azimuthal Phase Encoding Coils for NMR Formation Imaging
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Solution Overview
Problem
Current NMR well-logging technologies face challenges in accurately imaging subterranean formations with azimuthal resolution, particularly in harsh downhole environments, where existing methods struggle to provide detailed, high-resolution data on formation properties like porosity and permeability while drilling.
Innovation Solution
The implementation of azimuthal phase encoding (APEC) coils during NMR acquisitions, which encode spins with an azimuth-dependent phase, allowing for the analysis of T2 distribution profiles along the borehole and enabling the evaluation of azimuthal formation data, combined with inversion algorithms to estimate formation properties such as porosity, bound fluid volume, and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NMR well-logging methods are used, then basic formation properties can be measured, but azimuthal resolution and imaging accuracy are insufficient
Solution Approach 1:
The patent introduces azimuthal phase encoding that adds an angular dimension to the NMR measurements. By encoding the phase of nuclear spins with azimuthal information, the system transitions from conventional radial measurements to three-dimensional spatial localization (radial, azimuthal, and longitudinal dimensions), thereby achieving azimuthal resolution without proportionally increasing device complexity
Solution Approach 2:
The patent modifies the NMR measurement parameters by applying azimuthal-dependent phase encoding gradients. These gradient fields vary the phase accumulation of spins based on their azimuthal position, enabling angular resolution through parameter modulation rather than through complex hardware redesign
2Loss of information
If azimuthal phase encoding is implemented, then imaging accuracy and azimuthal information are improved, but the complexity of data processing and inversion algorithms increases
Solution Approach 1:
The patent applies phase encoding gradients during the NMR acquisition process to pre-imprint azimuthal position information onto the spin phases. This preliminary encoding of spatial information allows for more straightforward reconstruction algorithms, as the azimuthal dependencies are already embedded in the measured signals rather than requiring complex post-processing to extract
Solution Approach 2:
The patent employs iterative inversion algorithms that use feedback from the measured NMR signals to reconstruct azimuthal images. The reconstruction process continuously refines the estimated formation properties by comparing predicted signals with actual measurements, thereby recovering azimuthal information systematically while managing computational complexity through iterative optimization
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 accuracy and resolution of NMR imaging in logging-while-drilling contexts, providing valuable azimuthal information for geo-steering and improving the characterization of subterranean formations by enabling detailed porosity and permeability measurements.
Implementation Method 1
Nuclear Magnetic Resonance (NMR) tools used for well-logging or downhole fluid characterization measure the response of nuclear spins in formation fluids to applied magnetic fields
Implementation Method 2
A permanent magnet that produces a static magnetic field at a desired test location
Implementation Method 3
The magnetization vector precess around the static field at the Larmor frequency
Implementation Method 4
A transmitter antenna produces a time-dependent radio frequency magnetic field that has a component perpendicular to the direction of the static field
Data Source
AI summary
Systems and methods are provided for investigating a downhole formation using a nuclear magnetic resonance (NMR) tool. While the tool is moving through the borehole, the formation is magnetized and resulting signals are obtained. In accordance with the present approach, the acquired signals can be resolved azimuthally and/or laterally and can be reconstructed to obtain an indication of a parameter of the formation at multiple locations along the length of the borehole.