Suhas Vasant Bodwadkar's dissertation
by
Suhas Vasant Bodwadkar, Ph.D.
University of Texas at Austin, 1996
Supervisors: M. M. Sharma
J. C. Reis
The potential of gamma rays to characterize porosity and lithology of
cores has been evaluated. Gamma-ray attenuation can provide rapid, accurate,
and nondestructive measurements of these parameters at a desired scale.
Experimental set-up and procedures for determining porosity and
lithology using gamma rays have been developed. Sources in the Compton
scattering and photoelectric effect range were used. Equations for the
uncertainties in the measurements are presented.
The porosity measurements have been experimentally validated against
porosities measured using ArchimedesÕ method on a variety of lithologies and
over a range of porosities. Measurements for both air- and water-saturated
samples agreed well with each other. The error in gamma-ray porosity increases if the fluid saturations and the lithology are completely unknown.
The lithology of cores was obtained using a gamma-ray source in the
photoelectric effect range. The procedures for the lithology determination
were validated using samples of known lithology. The effect of clays on the
lithology measurements is presented. Theoretical calculations show that the
presence of clays up to 15 to 25% by volume (of the total rock volume) may not
interfere with the lithology measurements. The measurements in the
photoelectric range can also be used to detect the presence of heavier
elements.
Small scale heterogeneities in composition, porosity, and grain density were characterized using multiple measurements on a core. Statistical analysis of the data is useful in quantifying the heterogeneity. Theoretical analysis
has been done to show that with the use of more sources, better understanding
of mineralogy, and hence better estimate of the grain density, is possible.
In another application, the use of cesium measurements in particle settling experiments has been demonstrated.
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