Experimental Study on the Kinetics of Adsorption of CO₂ and CH₄ in Gas-Bearing Shale Reservoirs

Abstract

Knowledge of the kinetics of adsorption of CO2 and CH4 on shales is essential for the optimization of the technique of enhanced gas recovery by CO2 injection. In this paper, the experiments of adsorption kinetics of CO2 and CH4 on marine Wufeng (WF) shale and continental Yanchang (YC) shale at 318, 338, and 358 K over the pressure range of 3.0–8.0 MPa were conducted by a volumetric method. Results show that the adsorption processes of CH4 and CO2 on the shales can be described as an initial rapid adsorption stage and a slow sorption stage. The unipore model can simulate the kinetics data of CO2 and CH4 well. The diffusion coefficient (D) of gas increases with the increase of pressure. High temperatures will help to improve the diffusivities of CO2 and CH4. The order of magnitude of D of CO2 and CH4 on the two samples is 10–11 m2/s. The diffusion activation energies (E a) of CO2 and CH4 on YC shale are 3.37 and 10.15 kJ/mol, respectively, and E a of CO2 and CH4 on WF shale are 1.33 and 3.56 kJ/mol, respectively. The E a value of CH4 greater than that of CO2 indicates that CH4 diffusion in shale formation is more difficult and needs to jump a higher potential barrier. There is a positive correlation of pressure with the adsorption rates of CO2 and CH4. As the temperature enhances, the gas adsorption rate reduces. The ratios of D of CO2, CH4, and N2 are 1.42:1.15:1.00 on YC shale and 1.72:1.38:1.00 on WF shale. The adsorption rates of CO2, CH4, and N2 on the shales exhibit a decreasing trend.

A new approach for modeling adsorption kinetics and transport of methane and carbon dioxide in shale

“… 4–10 The desorbed CH 4 from pores needs to be transported out of the shale, which decides the shale gas production rate. However, the studies of the adsorption kinetics and transport properties of CO 2 and CH 4 , which related to shale production rate, are still very lack 9–18 …”

“…The gas diffusion coefficient for gas in shale can be obtained by the unipore model and bidisperse model using the adsorption kinetic data 11–15 . The unipore model has mostly been used because of its mathematical simplicity.…”

“…The bidisperse model developed by Ruckenstein et al 19 accounts for both micropore and macropore diffusion in the matrix. The bidisperse model can adequately describe the CH 4 diffusion data at the initial time range for shale, whereas the unipore model cannot 15 . However, the bidisperse model generally uses linear equation for adsorption, which leads to a certain deviation between the modeling results and experimental data 13,14,19 .…”

Dynamics adsorption of the enhanced CH4 recovery by CO2 injection

“…There are relatively few studies on adsorption kinetics of CO 2 and CH 4 . The study of adsorption kinetics mainly focuses on the adsorption rate equation and the diffusion coefficient of CO 2 and CH 4 3–15 …”

Performance of free gases during the recovery enhancement of shale gas by CO2 injection: a case study on the depleted Wufeng–Longmaxi shale in northeastern Sichuan Basin, China

“…To promote the development of the shale-based CS-EGR technique, considerable work has been organized, in which significant achievements have been drawn (Iddphonce et al 2020). For example, it has been proven that the CO 2 -CH 4 displacement behavior differs in the shales from different sedimentary environments (Du et al 2019). Another example is that the CS-EGR efficiency is considerably affected by Edited by Yan-Hua Sun the CO 2 proportion in the injected CO 2 -N 2 mixture (Li and Elsworth 2019).…”