Geological CO₂ storage in heterogeneous saline aquifers: Insights into the mechanisms of thermal and density effects

Variations in brine density are crucial for both CO₂ plume migration and long-term geological CO₂ storage. These variations are primarily controlled by three factors: pressure buildup, CO₂ dissolution, and thermal effects. However, previous models have generally neglected these processes or focused mainly on density variations induced by CO₂ dissolution. This study establishes a comprehensive thermo-hydro-mechanical framework to capture CO₂ migration dynamics in heterogeneous saline aquifers, accounting for brine density variations driven by multiple factors. Eight heterogeneous scenarios, including both high- and low-permeability reservoirs, are constructed to represent realistic subsurface conditions. Results indicate that thermal effects generate a localized cold front in the near-wellbore region, where CO₂ thermodynamic properties are highly temperature-sensitive and differ by several-fold from those of the undisturbed reservoir. Additionally, thermal effects lead to a noticeable decrease in brine density and induce thermal deformation. Brine-density variation is governed primarily by pressure buildup and CO₂ dissolution. The incorporation of CO₂ dissolution in the thermo-hydro-mechanical model shortens the CO₂ plume length by more than 230 m. Pressure buildup is the primary driver for brine density increases in low-permeability reservoirs, whereas CO₂ dissolution plays a more significant role in high-permeability reservoirs. Furthermore, high-permeability reservoirs are more conducive to density-driven convection, where vigorous convective fingering enhances mixing and promotes solubility trapping. Cited as: Jin, A., Park, E., Li, C., Shi, W., Wang Geological CO₂ storage in heterogeneous saline aquifers: Insights into the mechanisms of thermal and density effects. Advances in Geo-Energy Research, 2026, 19(3): 216-230. https://doi.org/10.46690/ager.2026.03.02