In-situ X-ray micro-computed tomography imaging of the microstructural changes in water-bearing medium rank coal by supercritical CO₂ flooding

Carbon dioxide geosequestration into deep unmineable coal seams is a technique which can mitigate anthropogenic greenhouse gas emissions. However, coal composition is always complex, and some minerals such as calcite chemically react when exposed to the acidic environment (which is created by scCO₂ mixing with formation water). These reactive transport processes are still poorly understood. We thus imaged a water-bearing heterogeneous coal (calcite rich) core before and after scCO₂ injection in-situ at high resolution (3.43 μm) in 3D via X-ray micro-tomography. Indeed, the calcite- fusinite mix phase was partially dissolved, and absolute porosity and connectivity significantly increased. We thus suggest that such a process could be used as an acidizing method for enhanced coal bed methane (ECBM) production, thus significantly improving the permeability performance, CO₂ injectivity and the associated methane permeability.