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The effect of coal composition upon gas sorption and transmissibility of bituminous coal Clarkson, Christopher Raymond

Abstract

The effect of bituminous coal composition, particularly the organic fraction, upon gas sorption and transmissibility is investigated. Micropore capacities of bituminous coals, determined from low pressure carbon dioxide adsorption, show a general increase with total and structured vitrinite content. Conversely, micropore capacities generally decrease with an increase in inertinite and mineral matter content. High pressure methane monolayer capacities show a similar trend. Micropore size distributions indicate an increase in the total number of micropores and a slight decrease in mean pore diameter with vitrinite content. Mesopore volumes and surface areas, determined through nitrogen sorption, show a general decrease with vitrinite content and increase with inertinite content of bituminous coal. Vitrinite therefore contains more microporosity and less mesoporosity than inertinite. Hysteresis loops of sorption isotherms indicate that mesopores of the coals studied are slit-shaped. Permeabilities of bituminous coals obtained through the use of a permeameter capable of measuring permeabilities on a bed-by-bed scale show that brighter coal lithotypes are more permeable than dull lithotypes. The order of decreasing permeability with lithotype is: bright> banded> fibrous > banded dull> dull. The increase in permeability with increased brightness of coals is due to the presence of abundant macrofracturing (cleating) in bright coal. For one sample, permeabilties were found to increase with vitrinite content.

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