NMR Multi-Phase Flow Measurement Using Gradient Calibration
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Solution Overview
Problem
Existing magnetic resonance-based methods for measuring multi-phase flow regimes in pipelines are limited in accurately assessing the velocity profile of individual components, especially at low gas pressures or velocities, due to reliance on time-of-flight measurements and high-intensity magnetic field gradients, which are impractical and reduce measurement precision.
Innovation Solution
A method involving a magnetic resonance module and a pre-polarization module, where a radio-frequency pulse sequence is applied with and without a magnetic field gradient, allowing for calibration to determine the flow velocity of non-gas phases and correcting for gradient-induced attenuation, enabling precise measurement of gas and liquid phases' velocities and volumetric fractions without time-of-flight measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If time-of-flight measurements with high-intensity magnetic field gradients are used to measure flow velocity, then measurement range is extended, but measurement precision deteriorates and device complexity increases
Solution Approach 1:
The patent extracts the velocity measurement function from the traditional time-of-flight method with high-intensity gradients. Instead of using strong gradients to encode velocity, the invention applies weak or zero gradients during the measurement phase, separating the velocity encoding function (achieved through flow direction sensing and signal phase analysis) from the gradient intensity requirement.
Solution Approach 2:
The patent changes the magnetic field gradient parameter from high-intensity to weak or zero intensity during the measurement phase. This parameter change allows the system to maintain velocity measurement capability through alternative mechanisms (signal phase analysis, flow direction sensing) while avoiding the precision deterioration and complexity issues associated with high-intensity gradients.
2Speed
If time-of-flight measurements are used for multi-phase flow analysis, then flow velocity can be determined, but applicability to low gas pressures and velocities is limited
Solution Approach 1:
The patent applies preliminary polarization to the nuclei before the measurement phase. This preliminary action enhances the signal strength and improves the detectability of low-velocity and low-pressure gas phases, making the measurement system more versatile across different flow conditions.
Solution Approach 2:
The patent introduces flow direction sensing as an intermediary mechanism that works in conjunction with the magnetic resonance measurement. This intermediary allows the system to accurately determine velocity in low gas pressure and velocity conditions by analyzing the direction and phase of the flowing nuclei's signal.
3Measurement precision
If high-intensity magnetic field gradients are applied to spatially encode flow velocity, then velocity measurement capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the velocity encoding function from the high-intensity gradient system. Instead of relying on strong gradients for spatial encoding of velocity, the invention uses weak gradients combined with flow direction sensing and signal phase analysis to achieve velocity measurement, thereby reducing device complexity.
Solution Approach 2:
The patent replaces the mechanical/high-intensity gradient-based velocity encoding system with a signal-processing-based approach. By using flow direction sensing and phase analysis of the magnetic resonance signal, the system achieves velocity measurement without requiring complex high-intensity gradient hardware.
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 provides accurate characterization of multi-phase fluid flows, including low gas pressures and velocities, with improved precision and applicability to various flow directions, enhancing the measurement of gas and liquid components' velocities and volumetric fractions.
Implementation Method 1
A magnetic resonance-based method and device for the analysis of multi-phase flow regimes
Implementation Method 2
The spatial encoding of the temporal position of the resonant nuclei is performed by means of a linear magnetic field gradient in the volume that is probed by the excitation- and detection magnetic resonance coil
Implementation Method 3
applying to the fluid a radio-frequency pulse sequence at least once in the presence of a magnetic field gradient and at least once in the absence of a magnetic field gradient and measuring the intensity of a pre-determined number of spin echoes
Data Source
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Figure 3
Figure 4~5
AI summary
A method for assessing a gas phase in a flowing multi-phase fluid comprises flowing the fluid through magnetic resonance and pre-polarization modules and applying to the fluid a radio-frequency pulse sequence at least once with and at least once without a magnetic field gradient. The method further includes measuring an NMR signal. The method also includes using a calibration between the ratio of slope and intercept of the NMR signal and flow velocity for at least one non-gas phase with the gradient applied to determine that phase's velocity. A calibration between the signal intensity of the liquid phases as function of flow velocity is used, with and without gradient, to correct the gradient-induced attenuation of the liquid signals and to calculate a gradient-corrected signal intensity of the liquid phases without a magnetic field gradient. Additionally, the method includes subtracting the gradient-corrected signal intensity from the NMR signal to calculate the volumetric fraction of the liquid phase.