Influence of heterogeneity on dissolved CO2 migration in a fractured reservoir.

Dissolution trapping CO₂ is thought to be a permanent storage mechanism in deep saline aquifers. Brine saturated with CO₂ sinks to the bottom of the aquifer due to density-driven flow and is replaced by fresh brine with the remaining dissolution potential. This convective process persists and can effectively slow the spread of the CO₂ plume, thereby reducing the risk of leakage. The density-driven convection process is sensitive to reservoir heterogeneity. In this paper, the dynamics of dissolved CO₂ in a fractured saline aquifer are studied using a three-dimensional discrete fracture network matrix (DFM) model. The fracture density and heterogeneity between fractures are systematically analyzed. The highly connected fracture network provides preferential channels for the CO₂-rich plume to migrate to deeper regions of the aquifer. Several cases show that the increase of fracture density can effectively increase the dissolution flux in the domain, but the effect becomes less significant when the quantity exceeds a threshold value. The effects of two heterogeneous patterns (the density of high-permeability channels in the system and the correlation of the fracture aperture with the geometric size) in determining dissolution trapping are discussed. The heterogeneity of the fracture aperture is beneficial to finger formation and depth development. The results of this study increase the understanding of the dissolved carbon dioxide and plume dynamics in the fractured saline aquifers used for carbon sequestration. [ABSTRACT FROM AUTHOR]