Experimental CO2 Adsorption in Coal Versus Particle Size: Implications for CO2 Sequestration
Solano-Acosta, Wilfrido1, Maria Mastalerz1, and Arndt
1 Indiana Geological Survey, Bloomington, IN
2 Department of Geological Sciences, Indiana University, Bloomington, IN
Gas adsorption experiments are traditionally performed on finely crushed coal samples, < 250 mm. These experiments allow for the estimation of the maximum volumes of gas that a coal can retain at any given pressure/temperature. In this study, an experimental setup originally designed to test uncrushed coal cores was used to investigate the influence of particle size on CO2 adsorption characteristics in high-volatile bituminous coals from Indiana under conditions that are sub-critical for CO2. For these coals, standard high-pressure adsorption isotherm data at reservoir temperature, 70 ºF, indicate a maximum adsorption capacity of ~650 scf/ton at 400 psi.
Various coal samples were crushed and sieved to different grain sizes. The particles used in the experiment ranged from very coarse > 32 mm to the standard fraction used elsewhere during adsorption experiments. Our results show a distinct increase in adsorption with a decrease in particle size, probably as a result of the increase in surface area made available for CO2 and also the faster adsorption kinetics afforded by shorter diffusion pathways into the interior of smaller grains. A relative increase of 20 percent in CO2 adsorption was observed from the predominantly coarse fraction, 86 % >16 mm to the more finely dominated fraction, 100% <1 mm.
The dependence observed between grain size and adsorbed CO2 volumes may help predict the adsorption behavior of coal reservoirs under realistic temperature and pressure conditions. The evaluation of CO2 adsorption characteristics on finely crushed and uncrushed samples is critical for CO2 sequestration in coal beds.
AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004