Surface NMR Relaxation Time Estimation via Multi-Pulse Sequences
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current surface NMR technologies face challenges in accurately estimating NMR relaxation times, particularly T1, due to sensitivity to magnetic field inhomogeneities and complexity in measuring pore size and permeability, which are crucial for characterizing subsurface fluid-bearing formations.
Innovation Solution
The implementation of multi-pulse acquisition sequences with varied pulse moments and the use of adiabatic and composite pulses, along with data processing techniques that constrain the covariance of T1 and T2* relaxation times, to improve the estimation of NMR relaxation times and their spatial distribution, enabling more precise characterization of subsurface properties like pore size and permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-pulse or simple multi-pulse sequences are used, then the measurement process is simpler, but the accuracy of T1 relaxation time estimation deteriorates due to sensitivity to magnetic field inhomogeneities
Solution Approach 1:
The measurement process is divided into multiple separate acquisition sequences, each with its own preparatory pulse and subsequent pulses having different pulse moments. This segmentation allows independent optimization of each sequence to reduce sensitivity to magnetic field inhomogeneities while maintaining overall measurement accuracy.
Solution Approach 2:
Multiple periodic acquisition sequences are performed with varying pulse moments, and the results are combined through processing. This periodic repetition with variation enables averaging out the effects of magnetic field inhomogeneities and improves T1 estimation accuracy.
2Measurement precision
If multiple acquisition sequences with different pulse moments are used, then the accuracy of relaxation time estimation improves, but the measurement time increases
Solution Approach 1:
Instead of performing a single comprehensive measurement, multiple partial measurements with different pulse moments are acquired. Each sequence provides partial information that, when combined, yields the complete and accurate relaxation time estimation, accepting the time cost as necessary for precision.
3Adaptability or versatility
If standard processing methods are used, then the processing is simpler, but the ability to characterize pore size and permeability deteriorates
Solution Approach 1:
The processing method uses the measured NMR responses and estimated relaxation times as feedback to iteratively refine the characterization of pore size and permeability. This feedback loop enables more accurate formation characterization by continuously improving the estimates based on the acquired data.
Solution Approach 2:
The processing combines multiple types of information (NMR responses from sequences with different pulse moments, relaxation time distributions, covariance constraints) into a composite analysis framework. This composite approach enables simultaneous characterization of multiple formation properties including pore size and permeability that cannot be obtained with single-method processing.
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 precision of NMR relaxation time estimation, providing better characterization of subsurface formations by reducing the impact of magnetic field inhomogeneities and improving the sensitivity to pore size and permeability, thereby enhancing the measurement of T1 relaxation times.
Implementation Method 1
surface NMR measurement involves utilizing or generating a static magnetic field within a sample volume, emitting one or more electromagnetic pulses into the sample volume, and detecting NMR responses from the sample volume
Implementation Method 2
The preparatory pulses in the pulse sequences may comprise on-resonance pulses, adiabatic pulses, and/or composite pulses
Data Source
AI summary
NMR relaxation time estimation methods and corresponding apparatus generate two or more alternating current transmit pulses with arbitrary amplitudes, time delays, and relative phases; apply a surface NMR acquisition scheme in which initial preparatory pulses, the properties of which may be fixed across a set of multiple acquisition sequence, are transmitted at the start of each acquisition sequence and are followed by one or more depth sensitive pulses, the pulse moments of which are varied across the set of multiple acquisition sequences; and apply processing techniques in which recorded NMR response data are used to estimate NMR properties and the relaxation times T1 and T2* as a function of position as well as one-dimensional and two-dimension distributions of T1 versus T2* as a function of subsurface position.