Understanding the significance of in situ coal properties for CO2 sequestration: An experimental and numerical study



Over the years, there has been a rapid increase in atmospheric CO2 concentrations, from 280 ppm in 1850 to 360 ppm in 1998. Therefore, mitigation methods such as carbon sequestration in subsurface reservoirs have been suggested. CO2 sequestration is attractive, especially in relation to coal, with the additional potential benefit of CH4 recovery. However, the potential of CO2 sequestration is not well understood for various types of coals due to important in situ properties of coal. In this study, data from previous studies for coal permeability, density, moisture content, mineral content, vitrinite reflectance, compressive strength and temperature are compared with the CO2 adsorption results to understand the significance of these in situ coal properties on CO2 sequestration. To verify the findings, a custom-designed advanced core flooding apparatus is used to simulate the effects of various in situ properties on CO2 sequestration. This apparatus can test samples of 203 mm in diameter and up to 1000 mm in length. Hence, heterogeneity effects can be understood, as previous CO2 sequestration-related formulae have been based on coal samples of sizes ranging up to only about 100 mm. However, initially, a reconstituted coal core sample has been used to simplify the heterogeneity effects. Flow rates are estimated by analysing the lag of downstream pressures over time. With the use of a 203-mm-diameter and 816-mm-long reconstituted Victorian brown coal sample, flow rate reductions of 70% and 98% are observed for injection pressures of 2 and 4 MPa, respectively, due to CO2 injection. This study highlights the appropriateness of a candidate coal reservoir for CO2 storage in terms of in situ properties. Copyright © 2013 John Wiley & Sons, Ltd.