Nanoscale geomechanical properties of Western Australian coal

Geomechanical properties are of great importance in coal mining exploration, (enhanced) coal bed methane production and carbon geosequestration in deep unmineable coal seams. However, coal highly heterogeneous rocks, and conventional experimental methods (e.g. acoustic, seismic or unconfined compressive strength tests) only measure the cm-m scale bulk properties. Thus, we measured the geomechanical properties at nanoscale of Western Australian Collie coal. We mapped the nanoscale mechanical heterogeneity and correlated it with the sample's morphology (measured by SEM-EDS). It was found that the quartz and siderite in the coal had higher Young's moduli (up to 28.6 GPa), while the organic coal matrix had lower Young's moduli (from 3 GPa to 5 GPa), while the soft material kaolinite had the lowest Young's moduli (<3 GPa). We conclude that it is necessary to measure the geomechanical coal properties at nano/micro scale reliably assess and eventually facilitate field scale CBM/ECBM or CO₂ storage.