Adsorption kinetics of CH4 and CO2 on shale: Implication for CO2 sequestration

Abstract

The adsorption kinetic behavior of CH4 and CO2 in shale is critical for design and practice the CO2 sequestration with enhanced shale gas recovery. In this study, adsorption isotherms and kinetics curves of CH4 and CO2 in two shale samples were measured by the volumetric method at the temperature of 308.15 K, 323.15 K, 338.15 K and 353.15 K with the pressures up to 12 MPa. The pseudo-first-order (PFO) model, pseudo-second-order (PSO) model and Bangham model were used to describe the adsorption kinetics data. Furthermore, the influence of pressure and temperature on the adsorption kinetic behavior of CH4 and CO2 was clarified. The results show that the adsorption kinetic curves can be classified into three stages: rapid adsorption, slow adsorption and adsorption equilibrium stage. The fitting accuracy of the three kinetic models is in the order of Bangham > PSO > PFO. Moreover, the adsorption kinetics of CH4 and CO2 are highly dependent on pressure and temperature. The adsorption rate constant (kb) of CH4 and CO2 increases first and then decreases with increasing pressure. At the pressure below the supercritical pressure of CO2, the kb of CO2 shows a decreasing trend with the increase of temperature, which is the same as that of CH4. However, after exceeding the supercritical pressure of CO2, the variations in kb of CO2 with temperature presents an opposite trend as it increased with increasing temperature. Therefore, the pressure and temperature dependent adsorption kinetic behaviors requires consideration for optimizing engineering parameters in application of CO2 enhanced shale gas recovery and sequestration.