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

Abstract 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 scCO 2 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 scCO 2 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, CO 2 injectivity and the associated methane permeability. Highlights • The calcite-fusinite mix phase partially dissolved was observed in 3D as scCO 2 injected into water-bearing bituminous coal. • Morphological results showed the dissolved volume significantly increased the porosity and pore connectivity. • An environmentally friendly and relatively harm free acidizing method in ECBM was proposed. [ABSTRACT FROM AUTHOR]