Investigating pore geometry in heterogeneous porous samples using spatially resolved G₀-Δχ_app and G₀-Δν correlations

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Geophysics

Background:

• Magnetic susceptibility variations within porous media create internal magnetic field gradients.
• Characterizing pore size distribution and heterogeneity is crucial for understanding fluid transport and material properties.

Purpose of the Study:

• To develop and validate a spatially resolved 2D NMR pulse sequence.
• To correlate internal magnetic susceptibility gradients (G0) with apparent magnetic susceptibility differences (Δχapp) and spectral frequencies (Δν).
• To generate spatially resolved pore size distributions and assess sample heterogeneity.

Main Methods:

• A novel two-dimensional (2D) NMR pulse sequence was designed.
• The sequence measures correlations between G0 and Δχapp for pore size distribution.
• G0 and Δν correlations were used to evaluate sample heterogeneity.
• Measurements were performed on a heterogeneous porous sample with distinct glass sphere layers.

Main Results:

• Spatially resolved pore size distributions showed good agreement with previous non-slice selective methods.
• The 5-50 μm glass sphere layer exhibited higher heterogeneity than the 140-165 μm layer, as indicated by G0-Δν correlations.
• Slice selection was successfully validated on various samples.

Conclusions:

• The developed 2D NMR pulse sequence provides accurate spatially resolved pore size distributions.
• The method effectively quantifies sample heterogeneity based on magnetic susceptibility-induced gradients.
• This technique offers a valuable tool for characterizing complex porous materials.