The role of advection and dispersion in the rock matrix on the transport of leaking CO 2 - 1 saturated brine along a fractured zone

CO2 that is injected into a storage reservoir can leak in dissolved form because of 18 brine displacement from the reservoir, which is caused by large-scale groundwater motion. 19 Simulations of the reactive transport of leaking CO2aq along a conducting fracture in a clay20 rich caprock are conducted to analyze the effect of various physical and geochemical 21 processes. Whilst several modelling transport studies along rock fractures have considered 22 diffusion as the only transport process in the surrounding rock matrix (diffusive transport), 23 this study analyzes the combined role of advection and dispersion in the rock matrix in 24 addition to diffusion (advection-dominated transport) on the migration of CO2aq along a 25 leakage pathway and its conversion in geochemical reactions. A sensitivity analysis is 26 performed to quantify the effect of fluid velocity and dispersivity. Variations in the porosity 27 and permeability of the medium are observed in response to calcite dissolution and 28 precipitation along the leakage pathway. We observe that advection and dispersion in the rock 29 matrix play a significant role in the overall transport process. For the parameters that were 30 used in this study, advection-dominated transport increased the leakage of CO2aq from the 31 reservoir by nearly 305%, caused faster transport and increased the mass conversion of CO2aq 32 in geochemical reactions along the transport pathway by approximately 12.20% compared to 33 diffusive transport. 34