The mechanical properties of CO2-saturated coal specimens

摘要

To reduce the emission of CO2 into the atmosphere, it is proposed to store CO2 into deep un-mineable coalbeds. 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 CO2-ECBM and coalbed geo-sequestration operations. To investigate the effects of CO2 adsorption on the mechanical strength and stiffness of coal, 45 core specimens of Australian black coal from the Sydney Basin were tested. The behaviour of dry, water-saturated and CO2-saturated specimens were investigated at confining pressures up to 1.0MPa at room temperature. Results showed that triaxial compressive strength of CO2-saturated coal is 20% less than that of water-saturated coal at confining stress of 1.0MPa. Hoek & Brown failure criterion was used to explain the behaviour of coal and it was found that the rock constant mi of CO2-saturated coal is significantly lower. It can be concluded that CO2 changes the mechanical behaviour of coal by changing the way cracks and fractures propagate and by changing the surface properties of fractures.