Effect of vertical permeability trends on CO2 trapping in deep saline aquifers

Irina Spivakova, Ilya Bayanov, Peyman Pourafshary, Masoud Riazi, Reza Khoramian

2026

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DOI 10.1016/j.engeos.2026.100630
Data confidence 70 medium
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Abstract

Geological storage of CO 2 in deep saline aquifers has been widely proposed as a long-term mitigation option. However, the influence of vertical reservoir heterogeneity on CO 2 trapping mechanisms remains insufficiently quantified, representing a critical gap. This study uses high-resolution 2D compositional reservoir simulations to systematically evaluate how vertical permeability trends control CO 2 trapping in deep saline aquifers. A vertical cross-section model with 5 years of CO 2 injection followed by 195 years of monitoring was developed, covering heterogeneity levels from homogeneous to highly heterogeneous (V DP = 0.11–0.93), and explicitly comparing upward-decreasing (UD) and upward-increasing (UI) permeability architectures. The results show that permeability architecture fundamentally controls trapping behavior. At low heterogeneity, both trends exhibit similar performance, with dissolution and residual trapping differing by less than ∼7% and ∼4%, respectively. At moderate heterogeneity (V DP ⁓ 0.5), UI enhances vertical connectivity, resulting in ∼25–30% higher dissolution after 200 years, while UD promotes earlier plume segmentation and residual trapping. At high heterogeneity (V DP ≥ 0.85), UD profiles create effective vertical barriers that increase plume compartmentalization and maximize long-term immobilization, whereas UI cases maintain a large, connected gas cap and reduced trapping efficiency. Sensitivity analysis shows that injection-layer permeability variations (110–350 mD) affect trapping by less than ±5%, confirming that vertical permeability structure is the dominant control. Permeability trends also influence injectivity: low-permeability layers near the well increase bottom-hole pressure, while high-permeability bases maintain lower injection pressure. These findings provide practical guidance for site selection: in moderately heterogeneous sandstones (V DP ⁓ 0.3–0.5), UI trends favor efficient injection and enhanced early-time dissolution (∼50 years), whereas in highly heterogeneous reservoirs (V DP > 0.5), UD trends support long-term (century-scale) CO 2 trapping, albeit with higher injection pressure.