Evaluation of sandstone surface relaxivity using laser-induced breakdown spectroscopy

Area of Science:

• Geophysics and Geochemistry
• Materials Science
• Analytical Chemistry

Background:

• Nuclear magnetic resonance (NMR) relaxometry is crucial for analyzing pore sizes in porous materials.
• NMR data provides relative pore size distributions; absolute distributions require known surface relaxivity.
• Current methods for determining surface relaxivity can be time-consuming and require large samples.

Purpose of the Study:

• To introduce a novel method using laser-induced breakdown spectroscopy (LIBS) to evaluate surface relaxivity in sandstones.
• To establish a correlation between LIBS elemental analysis and NMR-derived surface relaxivity.
• To assess the potential of LIBS as a faster, more portable alternative for surface relaxivity calibration.

Main Methods:

• Measured NMR transverse and longitudinal relaxation times on sandstone samples.
• Calculated surface relaxivity using pore size distributions obtained from mercury injection capillary pressure (MICP) measurements.
• Employed multivariate analysis to correlate LIBS elemental data with calculated surface relaxivity.

Main Results:

• LIBS data accurately predicted longitudinal surface relaxivity (R²∼0.84) and transverse surface relaxivity (R²∼0.79).
• Regression analysis identified significant influences from elements including iron, manganese, cobalt, and titanium.
• LIBS offers advantages in speed, portability, and reduced sample size requirements compared to existing methods.

Conclusions:

• LIBS is a viable and efficient technique for determining surface relaxivity in sandstones.
• This method enables accurate calculation of absolute pore size distributions from NMR data.
• The LIBS approach shows promise for application to other porous materials beyond geological samples.