Variation in micropore capacity and size distribution with composition in bituminous coal of the Western Canadian Sedimentary Basin: Implications for coalbed methane potential

Abstract

The effects of lithotype, maceral and mineral contents on the micropore capacity and size distribution are investigated for a medium-volatile bituminous coal from the mid-Cretaceous Gates Formation of north-east British Columbia and a high-volatile bituminous coal from the Cretaceous of Alberta. Vitrinite content (vol.% mmf) ranges from 18 to 95 for the Gates coal and 36 to 85 for the Alberta coal. Ash yields (wt%) vary from 4.4 to 33.7 for the Gates coal and 1.2 to 10.6 for the Alberta coal. Dubinin-Radushkevich CO 2 micropore capacities (cm 3 g −1 mmf) measured at 273 K range from 23.7 to 43.9 for the Gates coal and 37.0 to 54.7 for the Alberta coal. Low-pressure Dubinin micropore capacities and Langmuir and BET monolayer volumes measured at 273 K generally increase with increasing total and structured vitrinite content and decrease with increasing inertinite and mineral matter content. The increase in micropore capacity with vitrinite content is due to an increase in the number of micropores, as demonstrated by Dubinin-Astakhov micropore size distributions. For the Gates suite, a sample with high total vitrinite and semifusinite contents has the largest micropore capacity, which may be due to the creation of micropore capacity in semifusinite through burning (charring). Micropore heterogeneity increases with an increase in inertinite and mineral matter content. Coal composition is important in determining the micropore capacity and size distribution and hence the gas capacity of bituminous coals.