Diffusion coefficient measurements for moving samples under strong magnetic field gradients.

Area of Science:

• Geophysics
• Petrophysics
• Nuclear Magnetic Resonance

Background:

• Nuclear Magnetic Resonance (NMR) is crucial for assessing oil well economic viability.
• Wireline Logging (WL) and Logging While Drilling (LWD) are primary NMR data acquisition methods.
• LWD NMR measurements face challenges due to tool motion (translation, rotation, vibration).

Purpose of the Study:

• To develop and validate a setup emulating LWD conditions for NMR measurements.
• To investigate the impact of LWD motion on diffusion coefficient measurements.
• To propose solutions for accurate diffusion coefficient determination under LWD conditions.

Main Methods:

• Developed a setup simulating LWD tool movement (sinusoidal motion).
• Utilized a single-sided magnet, RF probes, and a mechanical device.
• Investigated bulk samples and rock formations (Fontainebleau Sandstone, Berea Sandstone, Indiana Limestone).
• Employed Hahn spin echo sequences synchronized with sample movement.

Main Results:

• Demonstrated precise and accurate prediction of fluid diffusion coefficients in bulk and porous media.
• Identified signal phase modulation due to sample movement as a key challenge in LWD diffusion measurements.
• Validated the effectiveness of synchronized Hahn spin echo experiments for overcoming motion-induced artifacts.

Conclusions:

• Accurate diffusion coefficient measurements are achievable under LWD conditions with appropriate synchronization techniques.
• The developed methodology provides a pathway for reliable NMR-based petrophysical analysis during drilling.
• This research enhances the understanding and application of LWD NMR in the oil industry.