Laboratory studies of the effect of sorbed oil on proton nuclear magnetic resonance

Proton NMR (nuclear magnetic resonance) measurements were made of T-1 and T-2 relaxation times of water in saturated sands containing varying amounts of sorbed oil on the grain surfaces. The porosity, surface area, and grain density of the sands and the relaxation times of the extracted pore water were also determined experimentally. Sorption of oil changed the relaxation time of water in the saturated sands through changes in surface area and surface relaxivity, the parameter used to quantify the ability of the surface of the pore space to reduce NMR relaxation times. In some cases the addition of oil to the surfaces decreased the surface area, an observation that suggested the oil was coating the surface in a way to reduce surface roughness. When larger amounts of oil were added to the surface, surface area increased. The changes in surface relaxivity with the amount of sorbed oil were governed by the relaxivity of the clean, oil-free surfaces. In the Wedron sand, with a surface relaxivity typical of naturally occurring sands, the relaxivity decreased with the addition of oil to the surface of the sand grains. In the A-A sand, a clean, pure quartz sand, the relaxivity increased from a very low value for the oil-free sample to a higher value, interpreted to be that of the oil surface.