Отправлено: 11.11.14 09:31. Заголовок: Determining fractal dimension from nuclear magnetic resonance

Determining fractal dimension from nuclear magnetic resonance
data in rocks with internal magnetic field gradients
Hugh Daigle, Andrew Johnson, and Brittney Thomas

ABSTRACT
Pore size distributions in rocks may be represented by
fractal scaling, and fractal descriptions of pore systems
may be used for prediction of petrophysical properties
such as permeability, tortuosity, diffusivity, and electrical
conductivity. Transverse relaxation time (T2) distributions
determined by nuclear magnetic resonance (NMR) measurements
may be used to determine the fractal scaling of the
pore system, but the analysis is complicated when internal
magnetic field gradients at the pore scale are sufficiently
large. Through computations in ideal porous media and laboratory
measurements of glass beads and sediment samples,
we found that the effect of internal magnetic field gradients
was most pronounced in rocks with larger pores and a high
magnetic susceptibility contrast between the pore fluid and
mineral grains. We quantified this behavior in terms of pore
size and Carr-Purcell-Meiboom-Gill (CPMG) half-echo
spacing through scaling arguments. We additionally found
that the effects of internal field gradients may be mitigated
in the laboratory by performing T2 measurements with different
CPMG half-echo spacings and fitting the apparent
fractal dimensions determined by the NMR measurements
with a mod

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Мораль проста - чем ыше неоднородности тем больше проблем
Причем неоднородности IMHO могут быть и от железистых минералов