Abstract:

In order to explore the characteristics of storage-permeability and the heterogeneity within the coal macrolithotypes, the
medium-high rank samples of different macrolithotypes in Hancheng mining area, were studied using the low field nuclear magnetic
resonance technique, fine description and quantitative characterization of pore-fracture system and the difference in the effective
porosity within different macrolithotypes in Hancheng mining area have been obtained. Based on the cumulative amplitude curves
before and after centrifugation, the threshold T2C1 and T2C2, which can divide the pore-fracture system, was obtained, and the
reconstruction of proe size distribution of different macrolithotypes was established. The experimental results show that different
macrolithotypes of coal samples have significantly different T2 spectrum, which shows from the bright coal to the dull coal. The T2
spectrum from the double macropore type is gradually transformed to the double micropore type, and both of T2C cutoff value and
effective porosity show a gradually decreasing trend. The distribution of the pore-fracture system, which was obtained by the threshold
of T2C1 and T2C2, show that, from the bright coal to the dull coal, the pore-fracture structure of the reservoir transformed from the seepage
pore type to the comprehension type and the diffusion type.

Key words: macrolithotypes, storage-permeabiliy, NMR, effective porosity, threshold