Impact of intrinsic layered heterogeneity on CO2 convective-reactive dissolution in saline aquifers

Abstract

The heterogeneity of saline aquifers significantly influences CO₂ dissolution efficiency and convective-reactive transport dynamics, which still remains insufficiently understood. To address this knowledge gap, this study systematically evaluates the effects of three intrinsic layered heterogeneities (i.e., porosity, permeability, and reactant content) in saline aquifers on both the convective mixing behavior of CO₂ plumes and the chemical dissolution of CaCO₃. These investigations are conducted using a newly developed convective-reactive transport model. The results demonstrate that, compared to homogeneous aquifers, layered heterogeneity with decreasing porosity or reactant content significantly enhances CO₂ convective-reactive transport, leading to faster CO₂ full mixing with brine and complete CaCO₃ dissolution. In contrast, increasing porosity or reactant content with depth exhibits a negative effect on CO₂ dissolution efficiency. Permeability layered heterogeneity in aquifers inhibits CO₂ convective-reactive dissolution compared to homogeneous aquifers. Distinct CO₂-plume migration patterns emerge in different layered heterogeneous saline aquifers, primarily characterized by fingering, channeling, and compaction flow regimes. Additionally, the results also suggest that the evolution of Da number during CO₂ dissolution process can be adopted to evaluate the CO₂ dissolution efficiency. The findings of this work can provide a reference for screening the heterogeneous saline aquifers suitable for efficient CO₂ dissolution.