Dielectric and Nuclear Magnetic Resonance Characterization of Rock Types from Ewekoro, Eastern Dahomey Basin.
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Date
2014
Authors
Olatinsu, O.B
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Abstract
The purpose of optimum raw material preparation for cement production process is to
supply the burning process with a raw meal whose quality and homogeneity can ensure the
production of high-quality cement. Laboratory analyses play vital role in the evaluation and
classification of the raw materials. In this work, dielectric and Nuclear Magnetic Resonance
(NMR) measurements were conducted under ambient conditions to characterize limestone
and its associated rock raw materials (sandstone, shale and glauconite) from Ewekoro,
Eastern Dahomey Basin. While limestone, sandstone and shale are required in cement
production, glauconite is a problematic deposit as a result of its high resistance to burning.
Precision impedance analyzer (Agilent 4294) and NMR analyzers (MARAN-2 Ultra and
Bruker minispec mouse) were employed for the dielectric and NMR measurements
respectively. Dielectric measurement was carried out in the frequency range, 40 Hz to 110
MHz. All studied rock types in dry and partial water saturation conditions are governed by
Cole-Cole dielectric relaxation, i.e., a distribution of relaxation times and thereby establish
the multicomponent nature of these rocks. In the intermediate and high frequency range
(i.e. beyond the electrode-sample contact polarization region), Shale and glauconite were
found to have values of the four dielectric parameters (dielectric constant, dielectric loss,
conductivity and loss tangent) which are at least an order higher than those of limestone
and sandstone. Characteristic peaks are revealed in the loss spectra of all the rock samples in dry and partial water saturation conditions. Relaxation and critical frequencies show an
increase in the order: limestone<sandstone<glauconite<shale. While an increase was
observed in these two frequencies for limestone, sandstone and glauconite from dry state to
partial saturation condition, the opposite was found for shale. Transverse relaxation time T2
curves at full saturation provided better characterization of pore size and type than at partial saturation and these depict the NMR T2 relaxation rates in the order:
1/T2(shale)>1/T2(glauconite)>1/T2(limestone) and 1/T2(sandstone). NMR T2 distributions at
full brine-saturation showed that: shale has unimodal distribution; sandstone and glauconite
have bimodal distributions; while limestone has trimodal distributions. Also these
distributions revealed the presence of well-developed and more abundant micropores in all
the samples with T2 in the range, 402 - 504 μs. Mesopores with amplitudes much lower
than those of micropores are present in limestone, sandstone and glauconite with T2 range:
8.45 - 26.10 ms, 6.02 - 10.55 ms, and 9.45 - 13.26 ms respectively. Very low amplitude
macropores of T2 values, 90.26 - 312.16 ms, are only recognizable in limestone samples.
Samples with multiple peaks showed well-connected pore systems with sandstone having
the highest degree of connectivity. Dielectric constant and conductivity as intrinsic
properties of rocks correlate with overall NMR relaxation rate. Shale and glauconite with
fast NMR relaxation rates (i.e., greater effect from more abundant small pores with high
surface-to-volume, S/V ratio) correspond to samples with relatively high dielectric constant
and conductivity. On the other hand, limestone and sandstone with slow relaxation rates
(i.e., combined effect of large pores with low S/V ratio in addition to more abundant small
pores) correspond to samples with relatively low dielectric constant and conductivity. Each
technique and their combination, can serve as complimentary effective tools for rock characterization, especially in geological environment where problematic deposits exist.
Description
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos.
Keywords
Homogeneity , Nuclear Magnetic Resonance , Dielectric , Research Subject Categories::NATURAL SCIENCES::Physics::Nuclear physics
Citation
Olatinsu, O.B (2014), Dielectric and Nuclear Magnetic Resonance Characterization of Rock Types from Ewekoro, Eastern Dahomey Basin. A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 161pp.