A laboratory study to determine the effect of surface area and bead diameter on NMR relaxation rates of glass bead packs
Journal name: Near Surface Geophysics
Issue: Vol 12, No 2, April 2014 pp. 243 - 254
Special topic: Magnetic Resonance in the Subsurface
Info: Article, PDF ( 561.28Kb )
Price: € 30
A laboratory study was conducted to explore the relationship between pore size, pore surface-areato-volume ratio and NMR relaxation rates and to determine which geometric parameter best predicts the average NMR relaxation rate. NMR relaxation measurements were collected on watersaturated glass beads with controlled sets of bead diameters and surface areas. Four sets of beads were used with average diameters ranging from 55–1125 μm. The surface areas of the glass beads were altered by chemically treating the beads with a weak acid, a strong base and a cream commonly used to etch glass surfaces. Following the chemical treatments, the surface areas of the beads were quantified with krypton BET gas adsorption measurements. It was found that, for the range of bead diameters used in this study, relaxation did not strictly occur in the fast diffusion regime and, as such, the relaxation time associated with the peak of the largest mode in the distribution was found to more accurately represent the pore-scale geometry than the mean log relaxation time. Using the relaxation time associated with this peak, the results from this study show that the pore surface-area-to-volume ratio is a significantly better predictor of the surface relaxation rate than the mean grain radius (p = 0.014).