Methane and carbon dioxide adsorption-diffusion experiments on coal: Upscaling and modeling

Institute of Geology and Geochemistry of Petroleum and Coal, Aachen University (RWTH-Aachen), Aachen, Germany
International Journal of Coal Geology (Impact Factor: 3.38). 12/2004; 60(2):151-168. DOI: 10.1016/j.coal.2004.05.002


Numerical modelling of the processes of CO2 storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO2 and CH4 were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VRr=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to ∼3 mm at temperatures of 45 and 32 °C, using a volumetric experimental setup. CO2 sorption was consistently faster than CH4 sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than 2 with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions.Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO2 and CH4 that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated.Further, it was shown that an upscaling of the experimental and modelling results for CO2 and CH4 can be achieved by performing experiments on different grain size fractions under the same experimental conditions.In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.

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    • "Competitive adsorption behavior of CO 2 and CH 4 in coal seams and carbon nanopore has been reported [2,3,8–18]. Experiments with gas mixtures (CO 2 /CH 4 ) have shown that selective adsorption does not always favor CO 2 and there is clear evidence for preferential adsorption of CH 4 at low pressures [3] [15] [19]. Majewska et al. [19] observed unusually high affinity of bituminous coal for CH 4 over CO 2 at a pressure of 2.6 MPa and a comparable affinity at 4 MPa. "
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    ABSTRACT: Adsorption isotherms of carbon dioxide (CO2) and methane (CH4) provide crucial information for CO2 sequestration and exploitation of coal seam gas. In this work, we focus on the competitive adsorption behavior of CO2 and CH4 in micropores of an intermediate ranked bituminous coal by performing Monte Carlo (MC) simulations at different injection depths from 300 m up to 3280 m with varying injected gas compositions. An extended poromechanical model enables us to relate our simulation results of adsorption to volumetric strain in the coal. Our simulations show that (i) CO2/CH4 adsorption selectivity, defined as the ratio of the mole fractions of the two species in the adsorbed phase relative to the ratio of the mole fractions in the bulk phase, decreases with increasing injection depth for a fixed injected gas composition, (ii) at a given depth, CO2/CH4 adsorption selectivity decreases as the concentration of CO2 in the injected gas increases, (iii) CO2/CH4 adsorption selectivity appears to be a function of pressure and gas composition at a given temperature. The total adsorption increases with increasing concentration of CO2 in the injected gas at constant gas reservoir pressure. The CO2/CH4 adsorption selectivity decreases with increasing bulk CO2 mole fraction after an initial increase at low pressures, (iv) the volumetric strain has a direct correlation with the injected gas composition and increases with the concentration of CO2 in the injected gas. At 370.2 K the largest volumetric strain of 3.6% is predicted at 30 MPa for pure CO2 adsorption.
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    • "The potential storage of CO 2 in Italy has never been fully evaluated, but we are convinced that a general Italian survey could be helped by test-sites studies, as ECBM ones, and the two research activities could be parallel (Quattrocchi, 1999; Pizzino et al., 2002; Quattrocchi et al., 2003, 2004 a; Angelone et al., 2004; Miller et al., 2004; Voltattorni et al., 2005). Soon after the first challenging scientific results (Law et al., 2001; Wong et al., 1999, 2001; Mavor et al., 1999; 2002; 2004 a,b; Mac Donald et al., 2003; Gunter et al., 2004) coming from the ECBM scientific Community, strongly busy for the proximal ratification of the Kyoto Agreement (occurred in February 2005), as presented mostly at the GHGT international conferences since 1999 (Green House Gas Control Technologies), ECBM production (Fig. 1) and some challenging pilot-test projects and feasibility studies on ECBM built-up worldwide (Krooss et al., 2002; Busch et al., 2003, 2004; NOVEM, 2001, 2003; Yamaguchi et al., 2004; McIntyre et al., 2004; Reeves, 2004; Carroll and Pashin, 2004; Groshong et al., 2004; Gunter and Chalaturnyk, 2004; Su et al., 2005). "
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