Surface-to-volume ratio of ganglia trapped in small-pore systems determined by pulsed-field gradient nuclear magnetic resonance

Pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) measurements o f hydrocarbon diffusion are shown to provide a quantitative measure of the surface-to-volume (s/v) characteristics of slowly dissolving hydrocarbon ga nglia, trapped in a water-saturated porous medium, for systems with pore si zes below the limit of spatial resolution of magnetic resonance imaging (MR I). The porous medium is in the form of a packed bed of glass ballotini. Th e PFG NMR approach is validated in two ways. First, both MRT and PFG analys es are performed on the same system containing ballotini with a diameter of 1 mm. The s/v ratio of the dissolving ganglia determined by the two method s is the same to within the accuracy of the experimental data. Second, belo w the spatial, resolution limit of MRI, PFG NMR alone is used to characteri ze the s/v ratios of ganglia entrapped in two packings of ballotini with di ameters 0.1 and 0.5 mm, respectively. The sly data are then included into a one-dimensional advection-dispersion model of the ganglia dissolution proc ess. The resultant mass transfer coefficients obtained are in agreement wit h those obtained, under the same conditions of aqueous superficial how rate , following MRI analysis of hydrocarbon dissolution in larger pore structur es. (C) 2001 Academic Press