A Multi-Factor Comparative Study on H₂ and CO₂ Migration Behaviors in Saline Aquifers

In contrast to CCUS/CCS, research on UHS in saline aquifers remains limited. Comparative analysis of H₂ and CO₂ migration offers a basis for transferring CCUS/CCS insights to UHS. Thus, to investigate how multiple factors affect H₂ and CO₂ migration in saline aquifers, this paper constructs various 3D models considering porosity, permeability, pressure, temperature, salinity, and capillary pressure. Numerical simulation results show that (1) H₂ exhibits strong fingering and wide plume spread, with low solubility and weak residual retention. CO₂ shows compact, stable plumes with high solubility and strong residual retention. (2) Low porosity enhances lateral migration and residual retention, especially for CO₂. (3) Reduced vertical permeability (K_v) significantly suppresses the upward migration of CO₂ and strengthens residual retention, whereas its effect on the H₂ migration range is less than 5%. Low horizontal permeability (K_h) mainly restricts lateral spreading and only slightly increases residual retention, but the sensitivity of H₂ is lower than that of CO₂. (4) Increased pressure promotes the dissolution of H₂ and CO₂. The dissolved amount of H₂ increased by approximately 16.15%, and CO₂ by about 7.49%. The temperature rise increases the solubility of H₂ and decreases that of CO₂. H₂ increased by approximately 15.56%, and CO₂ decreased by about 13.82%. The increase in salinity inhibited the dissolution of the two gases. H₂ and CO₂ decreased by approximately 17.5% and 16.6%, respectively. Additionally, high salinity weakens the temperature sensitivity of gas solubility. (5) Ignoring capillary pressure underestimates residual retention. However, it is mainly reflected in an increase in the retention scale and does not change the trend of residual retention controlled by different variables. These insights provide a basis for applying CCUS/CCS experiences to UHS.