The sequestration of CO2 in saline aquifers represents a viable strategy for mitigating atmospheric CO2 emissions. Many studies show that CO₂ storage efficiency and plume movement are significantly influenced by aquifer heterogeneity, including variations in permeability, porosity, and stratigraphy. However, the influence of permeability heterogeneity across various correlation lengths with multiple independent realizations and the role of horizontal injection wells in CO₂ storage remains largely unexplored. Our study investigates numerically the migration and trapping of injected CO2 into a 2D heterogeneous model, using properties of the Jurassic aquifer of the Negev Desert, Israel. We consider uncorrelated and spatially-correlated heterogeneity in permeability and capillary pressure-saturation relationships, with correlation lengths of 50, 100, 300, 600, and 800 m, averaging over 15 realizations for each length. The simulated scenario is 30 years of supercritical CO2 injection at a constant rate through a horizontal well placed at the bottom of the aquifer, examining spreading and trapping over a period of 200 years after injection stopped. We used the TOUGH2 reactive flow simulator with the ECO2N equation of state module.

We find that spatially-correlated structural heterogeneity inhibits CO2 spreading and leakage into the caprock. In all cases, no mobile CO2 is found in the caprock at the end of the simulation. In the uncorrelated (random) heterogeneity or homogeneous cases, where the center of mass of the CO2 plume reaches the caprock negligible amounts of residually-trapped and dissolved CO2 are found in the caprock plumes generate irregular shapes and reside at the aquifer's bottom, thus improving storage safety by limiting CO2 penetration into the sealing layers.