RF Flip Angle Adjustment in Downhole NMR Tools

Solution Overview

Problem

Downhole NMR logging tools face challenges due to temperature-dependent magnetic field intensity variations, which degrade instrument performance and signal quality, particularly in wireline logging applications.

Innovation Solution

The integration of real-time RF flip angle and pulse width adjustments based on temperature measurements, using a temperature sensor and controller to maintain optimal magnetic field intensity and antenna sensitivity, is implemented in the NMR logging tool, incorporating a permanent magnet and soft magnetic core to mitigate temperature effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If temperature compensation is implemented through real-time RF flip angle and pulse width adjustments, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

ImproveNMR measurement precisionVSAvoidinstrument complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system performs preliminary calibration at different temperatures to establish lookup tables containing optimal RF flip angles and pulse widths for each temperature condition. During actual measurements, the pre-calibrated values are retrieved and applied based on the current temperature reading, eliminating the need for complex real-time calculations and simplifying the measurement process while maintaining high precision

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A temperature sensor continuously monitors the magnet assembly temperature and feeds this information to the controller, which automatically adjusts the RF flip angle and pulse width parameters based on the measured temperature and corresponding lookup table values. This closed-loop feedback mechanism ensures measurement precision is maintained across varying temperatures without requiring manual intervention or complex real-time optimization algorithms

Inventive Principle:

Principle #23Feedback

2Reliability

If real-time temperature monitoring and parameter adjustment systems are added, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improveinstrument stabilityVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system performs preliminary calibration at different temperatures to establish lookup tables containing optimal RF flip angles and pulse widths for each temperature condition. During actual measurements, the pre-calibrated values are retrieved and applied based on the current temperature reading, eliminating the need for complex real-time calculations and simplifying the measurement process while maintaining high precision

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A temperature sensor continuously monitors the magnet assembly temperature and feeds this information to the controller, which automatically adjusts the RF flip angle and pulse width parameters based on the measured temperature and corresponding lookup table values. This closed-loop feedback mechanism ensures measurement precision is maintained across varying temperatures without requiring manual intervention or complex real-time optimization algorithms

Inventive Principle:

Principle #23Feedback

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 signal-to-noise ratio (SNR) and maintains optimal NMR measurement performance across varying temperatures, ensuring consistent data quality and instrument stability during downhole measurements.

Implementation Method 1

there is variation of the magnetic field with temperature. A magnetic field's strength, in part, is characterized by its remnant flux density (Br). Magnetic field's remnant flux is temperature dependent.

Methodology Applied

Scientific EffectTemperature-dependent magnetic field variation: Magnetism

Implementation Method 2

The ability to mitigate the effects of magnetic field intensity variation is of direct relevance to NMR logging

Methodology Applied

Scientific EffectTemperature sensing:

Implementation Method 3

RF flip angle adjustment in a downhole NMR tool

Methodology Applied

Scientific EffectRF flip angle adjustment:

Implementation Method 4

Nuclear magnetic resonance (NMR) logging is among the most important methods that have been developed for rapid determination of such parameters

Methodology Applied

Scientific EffectNuclear magnetic resonance:

Data Source

PatentUS10996365B2RF flip angle adjustment in a downhole NMR tool

Publication Date: 2021.05.04 HALLIBURTON ENERGY SERVICES INC

AI summary

A logging instrument for estimating a property of a formation is provided. The instrument includes a magnet to generate a magnetic field. The instrument also includes pulse sequencer circuitry that supplies radio frequency (RF) signals. The instrument additionally includes an antenna system configured to transmit the RF signals and to obtain nuclear magnetic resonance (NMR) measurements of the formation in response to the transmitted RF signals. In one aspect, the logging tool contains a temperature sensor configured to obtain temperature measurements of the magnet. The instrument additionally includes a control unit communicatively coupled to the temperature sensor, the antenna system and the pulse sequencer circuitry and configured to receive the temperature measurements and selectively adjust operating parameters of the pulse sequencer circuitry based on the received temperature measurements in order to maintain optimal intensity of the magnetic field.