The effects of CO ₂ injection on the geomechanical behaviour of Australian brown coal: Uniaxial testing

Plans for the sequestration of CO ₂ in unminable coal seams require the effective retention of the stored gas within the coal seam. If CO ₂ is to be retained within a coal seam, the formation of flow paths that allow the escape of sequestered CO ₂ to local fault zones must be controlled. In assessing the risk of fracture related CO ₂ escape, an understanding of the effect that the introduction of CO ₂ has on the geomechanical behaviour of coal is critical. The influence that adsorbed CO ₂ has on the strength of coal and its susceptibility to fracturing is of particular importance, since studies outlined in geomechanical literature imply that the adsorption of CO ₂ on coal causes a significant reduction in its strength. This paper presents experimental results for an investigation carried out to explore the effect of CO ₂ on the strength of brown coal. Preliminary results from uniaxial testing suggest that the adsorption of CO ₂ causes a decrease in the strength and modulus of elasticity of brown coal. Thus, geomechanical aspects of coal seam CO ₂ sequestration may become an important consideration in assessing long term feasibility of the storage process.