Effect of Water Content and Salinity on CH<sub>4</sub>/CO<sub>2</sub> Competitive Adsorption in Organic and Clay Nanopores: A Molecular Perspective
Chenyue Xie, Jingwei Huang, Shu Jiang, Hui Zhao, Zhengbin Wu
Abstract
CO 2 injection into shale gas reservoirs has been identified as a promising technique for enhancing shale gas productivity and achieving permanent CO 2 sequestration. The vast nanopores present in shale offer considerable space for CO 2 storage. However, it is often observed that shale nanopores can be filled with water, which inevitably affects the storage potential for CO 2 . In this work, molecular dynamics simulations are employed to investigate the influence of water and salinity on CO 2 adsorption behavior and storage capacity in both organic and clay nanopores. Simulation results show that the presence of water occupies the accessible adsorption space, resulting in a lower storage capacity of CO 2 . At the water content of 0.06, 0.12, and 0.18 g/cm 3, the reduction in CO 2 adsorption reaches 9.9, 17.1, and 22.2% in kerogen, respectively, greater than 3.4, 12.1, and 19.6% in K-illite. An enhancement in pore size can alleviate the CO 2 loss caused by water. The additional NaCl ions result in a further reduction in the adsorption capacity of CO 2 . The van der Waals interaction dominates the fluid–surface interaction. A higher interaction energy can be observed in kerogen for CO 2 with reduced mobility, indicating the potential for CO 2 geological storage. Subsequently, the CO 2 storage capacity in the shale pores is evaluated. The kerogen displays a higher storage amount for CO 2 than that for K-illite in any case. The presence of water significantly reduces the CO 2 storage capacity by 46.4 and 40.6% in kerogen and K-illite at 0.18 g/cm 3, respectively. This work provides an insight into the CO 2 adsorption behavior and storage capacity in shale nanopores under water and salinity environment.