Numerical investigation of CO₂ plume migration and trapping mechanisms in the sleipner field: Does the aquifer heterogeneity matter?

The urgent need for efficient carbon sequestration techniques to mitigate greenhouse gas emissions emphasizes understanding CO₂ storage in saline aquifers. This study investigates the influence of aquifer heterogeneity on CO₂ plume migration and trapping mechanisms through comprehensive numerical simulations, utilizing data from the Sleipner field. This research uniquely integrates a field-scale model with advanced parameterization of heterogeneity, offering new insights into CO₂ geo-storage efficiency. The goal was to determine how varying degrees of geological heterogeneity influence CO₂ storage efficiency, focusing on structural, solubility, and residual trapping mechanisms. A three-dimensional (3D) compositional model was developed based on the Sleipner field data, incorporating nine permeable sand layers interbedded with thin shale barriers to capture geological heterogeneity. The model was calibrated using seismic profiles, and heterogeneity was quantified using the Dykstra-Parsons (DP) coefficient to simulate a range of permeability distributions. Multiple scenarios were analyzed to assess the impact of heterogeneity on trapping mechanisms and plume dynamics over a 1000-year. Key findings demonstrate that geological heterogeneity alters the balance among CO₂ trapping mechanisms. Approximately 80 % of CO₂ was structurally trapped under cap rock and shale barriers during injection. Post-injection, heterogeneity promoted solubility trapping while diminishing residual trapping, particularly at higher DP values (0.25 and 0.4). These cases exhibited a higher CO₂-brine contact area and longer density fingers, increasing brine phase instability and enhancing CO₂ dissolution. In contrast, the homogeneous case (DP = 0) achieved the highest residual trapping efficiency. The study further revealed that neglecting heterogeneity leads to underestimation of CO₂ plume migration distances, compromising storage security predictions. Models with higher heterogeneity also exhibited a substantial increase in the volume of aquifer rock saturated with dissolved CO₂. This study's novelty lies in providing a detailed analysis of the role of geological heterogeneity on CO₂ trapping efficiency and plume dynamics by integrating multiple relative permeability data sets across the heterogeneous formations. The results underscore the critical importance of incorporating geological heterogeneity into CO₂ storage models for accurate long-term predictions of CO₂ storage efficiency and security.