Dynamic micro-CT study of gas uptake in coal using Xe, Kr and CO2

The physics of gas uptake in coal constrains the feasibility of coal seam gas extraction and carbon sequestration in coal measures. While X-ray tomography using xenon as an X-ray opaque tracer gas has been used in the past to study gas uptake in coal specimens, synchrotron sources enable high-resolution micro-tomography datasets of high quality to be acquired in minutes adding the ability to quantify the dynamics of gas sorption over time in five coals of similar rank on the microscopic scale. In the present work we describe a synchrotron micro-computed-tomography (micro-CT) study of gas uptake in coal using Xe, Kr and CO2 gases. Measurement of gas uptake over time for Xe and Kr in different specimens and of CO2 induced swelling are reported, together with an analysis of gas diffusion profiles and their correspondence to those expected from diffusion models. The rate of penetration was CO2 > Kr > Xe in all cases, though the rates of penetration varied enormously between different coals. In some cases even 2 months was not enough to allow the Xe to equilibrate fully. The gas distribution was also shown to respond rapidly to flushing with CO2.