PORE STRUCTURE ANALYSIS OF COALS USING LOW FIELD NMR MEASUREMENTS AND THERMOGRAVIMETRY ANALYSIS

摘要

Four different coals were studied using a combination of T2,T1,FID and solid echoes measurements on saturated plugs and degassed cuttings.These measurements were performed on two NMR spectrometers working at a proton Larmor frequency of 2 and 23 MHz.The measurements on saturated plugs allow the characterization of the cleats,and the measurements on degassed cuttings allow the characterisation of the matrix.For the latter,thermogravimetry coupled with mass spectral analysis were also performed.The results indicate a coherent measurement of liquid protons from NMR and thermogravimetry when the FID decay is analysed using a combination of Gaussian and exponential functions.This allows the distinction between solid and liquid fractions and consequently an accurate estimation of the porosity of the samples.For the four types of coal studied,microporosity represents a significant fraction of the total porosity(from 0.41 up to 0.91) and can be grossly underestimated when using usual NMR petrophysical analysis.