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Abstract

The dependence of the proton nuclear magnetic resonance parameter, T₁ on surface wettability, grain size, and pore fluid chemistry was investigated using laboratory prepared silica sand packs. A pulsed proton NMR spectrometer, with a proton Larmour frequency of 90 MHz, was used to obtain the T₁ relaxation data. Pore fluid T₁ data were found to be dependent on the surface wettability of the sand packs. An observed difference in T₁ of approximately 1 second was obtained between 100% water-wet and 100% oil-wet sand packs, when the pH of the pore fluid was neutral. This difference in T₁ between the water-wet and oil-wet samples when saturated with distilled water, was observed for a range of different pore sizes. T₁ relaxation time was found to depend on sand pack grain size in both the water-wet and oil-wet samples. This indicated the presence of surface relaxation in the samples. Calculated surface relaxivities produced average values of 1.2 x 10-₃ cm/s and 2.6 x lO-₄ cm/s for the water-wet and the oil-wet samples respectively. Pore fluid chemistry was found to affect T₁ relaxation measurements in water-wet and oil-wet sand packs. Experimental results indicated that although T₁ was unaffected by pore fluid salinity it was dependent on the pore fluid pH. Results showed that as pore fluid acidity increased, T₁ relaxation times decreased in both the water-wet and the oil-wet sand packs. This enhanced relaxation at lower pH's was attributed to increased pore fluid relaxation at the grain surfaces.