A macro-scale view of the influence of effective stress on carbon dioxide flow behaviour in coal: an experimental study

Abstract

Existing studies highlight the uncertainty in the process of CO₂ sequestration in deep coal seams, mainly due to the associated CO₂ adsorption-induced coal matrix rearrangements. This complexity is further increased by the highly heterogeneous nature of the coal mass which causes issues in reproducing field conditions under laboratory conditions. The main objective of this study is therefore to determine the permeability behaviour in coal for CO₂ flow using macro-scale reconstituted coal specimens (203 mm in diameter and 1000 mm in length), particularly under various effective stress conditions. A series of core flooding experiments was conducted on Australian brown coal, using an advanced core flooding apparatus, for a range of CO₂ injection pressures and axial stresses. According to the findings, CO₂ permeability decreases with increasing CO₂ injection pressure, and the reduction is greater for super-critical CO₂ at greater depths. The critical zone of influence for CO₂ injection into a selected coal seam is greater at lower injection pressures and at shallow depths, and it reduces with increasing CO₂ pressure and seam depth. CO₂ storage capacity in a selected coal seam is greater at lower depths and higher CO₂ injection pressures. However, the reduction of CO₂ storage capacity with depth was not very significant, which is important for field CO₂ sequestration projects, which normally use deep seams to store CO₂.