NMR responses to kaolinite in sand

Four sand size fractions of freshly crushed quartz saturated with brine were characterized petrophysically and petrographically followed by proton NMR measurements of longitudinal (T1) relaxation time behaviour. When kaolinite is added to the various quartz sand fractions, an increase in the NMR relaxation rate is observed. This continuously increases up to a "break point," which is assumed to coincide with an amount of kaolinite sufficient to cover all quartz surfaces. It is suggested that this increase is caused by a combined effect of an increased surface area and a higher surface relaxation strength (p) of the kaolinite.