A laboratory study of the effect of clay, silt, and sand content on low-field nuclear magnetic resonance relaxation time distributions

We have developed a laboratory nuclear magnetic resonance (NMR) study to investigate the effect of clay, silt, and sand content on the NMR relaxation time distribution. Transverse NMR relaxation times (T-2) are determined for water-saturated unconsolidated sediment mixtures of 1%-60% kaolinite clay, 5%-85% silt-size glass beads. and 8%-94% quartz sand by mass. Nearly all of the mixtures are characterized by a unimodal T-2 distribution. When clay is present in quantities greater than 10%, the clay content dominates the response. For these samples, the mean-log relaxation times (T-2ML) range from 0.03 to 0.06 s, regardless of silt or sand content. For mixtures with <10% clay, T-2ML decreases with increasing clay content. When the clay content is kept the same, T-2ML, decreases with increasing silt content and increases with the increasing sand content. The strong effect of the clay content on the NMR response is due to the high specific surface area of the clay and the distribution of clay throughout the samples. These results will help improve the interpretation of NMR field data in soils and unconsolidated sediments.