CO₂ long-term diffusive leakage into biosphere in geological carbon storage

Prediction of CO₂ leakage into biosphere is very important for risk assessment in geological carbon storage projects. Underground CO₂ can be transported into biosphere through short term leakage due to fractures of wellbores or cap rocks, which has been extensively investigated, and long term leakage due to diffusion, which has few relevant studies. This paper presents a diffusive model for CO₂ gradual leakage into biosphere during a long period after CO₂ injection. First, the paper describes a general diffusive model with long term secondary trapping effects for CO₂ fluxes from underground into biosphere. Secondly, a simplified one-dimensional model is presented and solved for the CO₂ concentrations in groundwater. The results show that the groundwater CO₂ concentration will reach the maximum value at about 50th year after CO₂ injection and then slowly decrease due to secondary trapping effects. Moreover, the partition coefficient is the dominant parameter for predicting the groundwater CO₂ concentration while the convective mass transfer coefficient plays an insignificant role.