NMR RF Coil Spatial Resolution via Deconvolution
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Solution Overview
Problem
Current NMR technologies face limitations in achieving high spatial resolution for measuring fluid content in rock samples due to the finite length of NMR radio frequency coils, particularly in applications involving whole core logging and reservoir measurements, where the sample length exceeds the coil length, leading to end effects and reduced sensitivity.
Innovation Solution
A method involving the use of a standard sample with a known fluid content to determine a response map of the NMR rf coil, allowing for the movement of both the standard and rock samples within the coil to measure signal intensities at multiple positions, and subsequent post-processing using matrix inversion or convex minimization to determine fluid content with high spatial resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the NMR rf coil length is increased to measure longer rock samples, then the measurement coverage is improved, but the spatial resolution deteriorates
Solution Approach 1:
The measurement process is segmented into multiple discrete positions along the rock sample. The NMR rf coil is positioned at multiple locations (e.g., 5-10 positions) along the length of the rock sample, and measurements are taken at each position. This segmentation allows the use of a shorter coil while achieving high spatial resolution through the accumulation of multiple localized measurements.
Solution Approach 2:
The problem is solved by transitioning from a single-dimensional measurement (one measurement over the entire sample length) to a multi-dimensional approach (multiple measurements at different positions along the sample). By adding the positional dimension and collecting data at multiple locations, the system achieves both long sample coverage and high spatial resolution without increasing coil length.
2Measurement precision
If the NMR rf coil length is decreased to improve spatial resolution, then the measurement precision is improved, but the measurement coverage deteriorates
Solution Approach 1:
The total measurement coverage is achieved by segmenting the sample into multiple measurement zones. A short rf coil is used to take measurements at discrete positions along the sample length, and these segmented measurements are combined to provide complete coverage of the entire sample while maintaining high spatial resolution.
Solution Approach 2:
The system performs preliminary measurements at multiple predetermined positions along the sample before combining the results. By pre-planning the measurement positions and taking measurements at each position sequentially, the system ensures complete sample coverage is achieved through the accumulation of multiple high-resolution localized measurements.
3Measurement precision
If multiple measurements are taken at different positions to improve spatial resolution, then the measurement precision is improved, but the measurement time increases
Solution Approach 1:
The measurement process is made continuous by systematically moving the rf coil or sample through a series of predetermined positions without interruption. Measurements are taken continuously at each position in sequence, eliminating idle time between measurements and maximizing the efficiency of the multi-position measurement approach.
Solution Approach 2:
The system uses periodic measurement cycles where the coil or sample is moved to the next measurement position after completing the current measurement. This rhythmic, periodic action of measure-move-measure-move optimizes the timing and reduces total measurement time compared to irregular measurement intervals.
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 enables accurate determination of fluid content in rock samples at resolutions finer than the coil length, overcoming end effects and providing quantitative measurements for samples with short relaxation times, applicable to both laboratory and well-logging applications.
Implementation Method 1
Nuclear Magnetic Resonance (NMR) tests are performed on a standard sample using a NMR radio frequency (rf) coil
Implementation Method 2
measuring a signal induced in the coil in response to the electromagnetic field
Data Source
AI summary
Certain techniques for Nuclear Magnetic Resonance (NMR) whole core logging are described. NMR tests are performed on a standard sample using a NMR radio frequency (rf) coil having a length. A response map of the NMR rf coil is determined. The response map relates multiple relative NMR rf coil positions to multiple relative signal intensities. The NMR tests are performed using the NMR rf coil on a rock sample containing fluid. A length of the rock sample is greater than the NMR rf coil. Fluid content in the sample is determined using results of the NMR tests using the NMR rf coil on the rock sample and using the response map for the NMR rf coil and a mathematical deconvolution to obtain high resolution. The same method can be used to obtain high spatial resolution NMR log measurement in the reservoir.