NMR Flow Measurement Using Pulsed Magnetic Field Gradients
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Solution Overview
Problem
Conventional flow measurement technologies, such as turbine and positive-displacement meters, disturb the flow pattern with moving parts, making it difficult to obtain accurate measurements of flow velocity and fluid viscosity, while non-invasive methods like NMR sensors face challenges with signal decay due to static magnetic field variations and require prior knowledge of fluid T1 distributions.
Innovation Solution
A nuclear magnetic resonance (NMR) tool and method that apply a radio frequency pulse sequence and magnetic field gradient pulse sequence to measure NMR signals, determining the phase characteristic and velocity distribution of flowing fluids without prior knowledge of T1 distributions, using a combination of NMR sensors and gradient coils to generate pulsed magnetic field gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional flow meters (turbine, positive-displacement) are used to measure flow velocity, then flow measurement can be performed, but the flow pattern is disturbed by moving parts making accurate measurement difficult
Solution Approach 1:
The patent replaces mechanical flow meters with an NMR-based measurement system that uses magnetic field gradients and radio frequency pulses to measure flow velocity without mechanical moving parts. The system calculates flow velocity from the phase shift of NMR signals caused by the motion of nuclei through the magnetic field gradient, eliminating the disturbance to flow pattern while maintaining measurement capability.
2Object-generated harmful factors
If NMR sensors are used for non-invasive flow measurement, then flow pattern is not disturbed, but static magnetic field variations cause signal decay making measurement difficult
Solution Approach 1:
The patent employs periodic magnetic field gradient pulses applied at specific intervals during the NMR measurement sequence. These pulsed gradients create the necessary phase shifts for velocity measurement while allowing the system to distinguish between signal variations caused by flow and those caused by static field variations. The periodic application of gradients enables reliable signal detection without being overwhelmed by static field noise.
Solution Approach 2:
The system dynamically adjusts the magnetic field gradient parameters and pulse timing to optimize signal quality. By varying the gradient strength and application timing based on the specific measurement conditions and fluid properties, the system maintains high measurement precision while minimizing the impact of static magnetic field variations on signal decay.
3Object-generated harmful factors
If NMR methods are used to measure flow velocity, then non-invasive measurement is achieved, but prior knowledge of fluid T1 distributions is required for computation
Solution Approach 1:
The patent enables the NMR measurement system to automatically determine fluid properties including T1 distribution without requiring pre-programmed knowledge or calibration data. The system performs self-characterization by analyzing the NMR signal decay characteristics and using this information to compute flow velocity and other parameters, eliminating the need for external reference data or complex setup procedures.
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
Enables accurate determination of flow velocity and fluid properties in downhole environments with improved signal-to-noise ratios and reduced sensitivity to fluid properties like viscosity, allowing for precise flow property measurements without disturbing the flow.
Implementation Method 1
The NMR sensor includes at least one coil that can produce pulsed field gradients (PFG) of defined amplitudes and time durations across the sample volume
Implementation Method 2
a nuclear magnetic resonance (NMR) tool and method are used to determine a velocity distribution or velocity image of a flowing fluid
Implementation Method 3
The NMR sensor includes an RF antenna for producing RF pulses. The magnetic moment of the RF antenna is substantially perpendicular to the magnetic moment of the static magnetic field
Implementation Method 4
The NMR sensor includes a coil (an RF antenna) for producing RF pulses... A typical sequence used in various applications is referred to as a spin-echo sequence
Data Source
AI summary
A nuclear magnetic resonance (NMR) method is used to determine a velocity distribution or velocity image of a flowing fluid in a downhole environment. The method comprises applying a radio frequency pulse sequence; applying a magnetic field gradient magnetic field and a gradient pulse duration; measuring a NMR signal; determining a phase characteristic of the NMR signal; and determining the velocity distribution or image of the fluid using the determined phase characteristic, the magnetic field gradient pulse parameters, and a time delay between gradient pulses.