Low-frequency NMR with a non-resonant circuit

Area of Science:

• Geophysics
• Electrical Engineering
• Nuclear Magnetic Resonance

Background:

• Nuclear magnetic resonance (NMR) measurements rely on tuned resonance circuits for signal transmission and reception.
• The efficiency of these circuits is often quantified by the coil quality factor (Q).
• Downhole environmental variations (temperature, salinity) cause significant fluctuations in circuit Q, leading to NMR measurement errors.

Purpose of the Study:

• To investigate the use of a non-resonant transmitter to decrease circuit sensitivity to Q variations.
• To develop a digitally controlled tuned receiver circuit for NMR applications.
• To demonstrate the feasibility of these circuits for common NMR experiments in well-logging.

Main Methods:

• Implementation of a non-resonant transmitter circuit designed for efficient power and current delivery to the NMR coil.
• Development of a receiver circuit with a digitally adjustable resonant frequency.
• Experimental validation of the proposed circuits across various NMR experiments.

Main Results:

• The non-resonant transmitter effectively reduces sensitivity to fluctuating coil Q values.
• The digitally tuned receiver allows for precise frequency control, adapting to changing conditions.
• Experimental data confirms the capability of these circuits to perform standard NMR experiments accurately.

Conclusions:

• Non-resonant transmitters and digitally tuned receivers offer a robust solution for NMR well-logging.
• These advancements mitigate errors caused by environmental variations, enhancing measurement reliability.
• The developed circuits enable consistent and accurate NMR data acquisition in diverse downhole conditions.