Molecular insights into the role of kerogen in retention of geologically sequestered CO₂ in shale formations during leakage scenarios

Abstract

The long-term security of geological CO₂ storage depends not only on the capacity of reservoir rocks to accommodate CO₂ but also on their ability to retain it under leakage scenarios. In this study, molecular dynamics simulations were used to investigate CO₂ behavior in illite-based shale pores with varying organic content and structural configurations. Three representative pore models were examined: a purely mineral illite pore, an illite pore fully packed with Type II-D kerogen, and a wider illite pore partially filled with kerogen. Under reservoir conditions, supercritical CO₂ was injected into each system, followed by a simulated leakage event. The findings reveal that, although pores with greater void volume store more CO₂ initially, their ability to retain it under leakage conditions is markedly lower. In contrast, kerogen-rich systems retain a significantly larger fraction of the adsorbed CO₂, especially in regions where kerogen is in direct contact with mineral surfaces. These results highlight the critical importance of organic content and mineral–organic interfacial structure in controlling CO₂ retention, offering molecular-level insights into the design of more secure geological storage systems.