Partially restricted diffusion in a permeable sandstone: observations by stimulated echo PFG NMR.
We demonstrate a variant, insensitive to eddy current effects, of an alternating pulsed field gradient technique designed to null the effect of background gradients in liquid-saturated porous media, using a 38 mm diameter sample of a natural sandstone. Measurements of the effective diffusivity confirm predictions of a decline as the square root of an effective diffusion time. A value of the ratio S/Vp for the dominant pores is extracted, yielding with T1 a value for the surface relaxivity. We test also a geometry-dependent data collapse recently suggested for a range of diffusion times and wavenumbers. The data agree with a sheet-like pore model for this granular sandstone, and fail to agree with a tube-like model; a pore length scale is also extracted.
Fordham
E J
EJ
Schlumberger Cambridge Research Ltd., UK.
Gibbs
S J
SJ
Hall
L D
LD
D004058:Diffusion; D009682:Magnetic Resonance Spectroscopy; D010539:Permeability; D016062:Porosity