An experimental investigation on mechanical behaviour of CO₂ saturated coal specimens

To reduce the emission of CO₂ into the atmosphere, it is proposed to store CO₂ into deep coalbeds which may also enhance the production of naturally-stored methane from coal formations. Many studies have been reported investigating the effect of CO₂ injection on the flow properties to provide a means of estimating the recoverable CH₄ and storable CO₂. However, assessment of the long-term integrity of stored CO₂ and the potentially damaging effects of CO₂ on the mechanical response of coal have been largely neglected. Understanding the geomechanical response of coalbeds to CO₂ injection can be crucial in site selection, in designing and planning coalbed geosequestration operations. To investigate the effects of CO₂ adsorption on the mechanical strength and stiffness of coal specimens, a series of triaxial experiments have been undertaken. Over 40 core specimens of Australian black coal from the Sydney Basin have been tested. The behaviour of water-saturated and CO₂ saturated specimens have been investigated at confining pressures up to 5.5 MPa at room temperature. Results showed that the strength and stiffness of CO₂ saturated specimens are significantly less than those of water saturated specimens.