Study on the response of formation fluid during geological storage of impure carbon dioxide

With the increasing urgency of global climate change and rising energy demand, carbon dioxide (CO2) geological storage has garnered significant attention as an effective method for mitigating greenhouse gas emissions. In the CO2 geological storage process, understanding the behavior of formation fluids is crucial to ensuring both the safety and long-term stability of storage. However, in actual storage operations, industrial CO2 emissions are rarely pure and typically contain a variety of impurity gases. As a result, CO2 must undergo purification prior to injection, a process that is not only time-consuming but also adds substantial costs. When considering the entire carbon capture and storage (CCS) chain, including capture, transportation, and purification, the total cost of operating current and future CCS projects can reach nearly one billion dollars. According to recent literature, the transportation and storage costs for CO2 can be as high as 45 USD per ton. In China, where cost sensitivity is especially high, these elevated expenses could significantly hinder the implementation of CO2 storage projects. Industrial CO2 emissions often contain not only CO2 but also other gases such as N2, O2, H2S, H2, and SO2. Direct injection of these gas mixtures into subsurface storage sites has the potential to reduce the overall cost of a CO2 geological storage project. However, the effects of impurity gases on storage mechanisms and long-term safety remain insufficiently understood and require further investigation. This study explores the response mechanisms of formation fluids in the context of non-pure CO2 geological storage, focusing on the influence of water-rock reactions, water-rock-gas interactions, permeability, solubility, and changes in the ionic composition of formation waters.

 

Keywords: water-rock reactions; impure CO₂; permeability; solubility; formation water ionic changes