Preliminary study on quantitative calculation of coal surface relaxivity based on particle packing method
The determination of the surface relaxivity ρ for coal and rock was used to quantita-tively characterize the relationship between their relaxation properties and pore size distribu-tion,focusing on large amount of coal particles produced during the drilling process,a method of coal ρ value calculation was proposed based on coal particle packing.A calculation model of the spherical coal detritor-spherical total pore structure was constructed.The coal samples from Ji 15 and Ji 17 coal seams in No.2 Mine,Pingdingshan Tianan Coal Industry Co.,Ltd.,were selected for model verification.The results show that the relaxation spectra of coal parti-cles with different particle sizes exhibit a similar three-peak shape,and the same water-saturat-ed coal particle deposits with different particle sizes can exhibit different relaxation response behaviors.The differences of T2m and φNMR values are mainly affected by water occurrence char-acteristics,coal debris wettability and packing mode.By linear fitting of T2-1 and φg/wgrain and 95％confidence interval distribution,it is proved that it is unreasonable to calculate the pore structure of coal rock directly with constant ρ value.The range of ρ values obtained by the cal-culation model of the matrix-total pore structure for coal cuttings with different shapes is dif-ferent,which indicates that the fluid diffusion path and contact characteristics between coal cuttings with different shapes are different,and it is easy to be different for the relaxation be-havior of coal cuttings deposits.Ignoring the T2b effect without considering the volume fluid effect among coal cuttings,the ρ value is likely to be too large.
low field nuclear magnetic resonancepore structuresurface relaxivityparticle packingnuclear magnetic porosity
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