Влиянием пирита и сидерита на ЯМР пренебречь нельзя!
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Impact of Paramagnetic Minerals on NMR-Converted Pore Size
Distributions in Permian Carynginia Shales
Yujie Yuan* and Reza Rezaee
https://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.8b04003 =================================
ABSTRACT: Pore size distribution (PSD) is a fundamental petrophysical parameter for shale formation evaluation. Nuclear
magnetic resonance (NMR), performing as a widely acknowledged technique, directly measures transverse relaxation time (T2),
which can be converted into PSD via surface relaxivity (SR). Technically, SR is utilized as a constant value in the entire
formation, nevertheless, the laboratory calculated SRs revealed that they are likely to vary with mineralogy and can be influenced
by Fe-bearing paramagnetic minerals, which could further affect NMR-converted pore structure properties. This study was
performed on Permian Carynginia shale samples to compare the NMR-converted PSD with that measured by mercury injection
capillary pressure (MICP). The surface relaxivity was calculated from the logarithmic mean T2 value (T2,lm) based on NMR
measurement and the surface to volume ratio (SVR) based on low-pressure nitrogen gas adsorption (LP-N2-GA). The results
show that Fe-bearing paramagnetic mineral contents are linear positively correlated with SR values, which were calculated to
range between 0.08 and 0.32 μm/s in our tested samples. The paramagnetic mineral of higher content expedites the NMR T2
surface relaxation rate, leading to the divergent shifts in NMR- converted PSD curves.
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Our findings indicate that surface relaxivity (SR), which
is largely influenced by Fe-bearing paramagnetic
minerals, would affect NMR conversions.
• SR in our tested samples, ranges from 0.08− to 0.32
μm/s and varies significantly with mineralogical
composition.
• Paramagnetic Fe-bearing the paramagnetic mineral
contents are intimately associated with surface relaxation. Linear correlations are presented between SR
values and pyrite/siderite concentrations.
• SR performs as the main cause for the deviation of
NMR-converted PSD compared to that in the MICP
results.
• The interpretation discrepancies in pore size distribution
and porosity between MICP and NMR are synthetically
influenced by the internal factors of the samples (e.g.,
paramagnetic mineral components, geometric pore
shape combinations, pore connectivity, etc.) and the
external factors involved in experiments (i.e., sample
pretreatment protocols, experimental working fluids,
NMR parameter
Отправлено: 15.06.20 11:48. Заголовок: Влиянием пирита и сидерита на ЯМР пренебречь нельзя!
