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 (Kv) 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 (Kh) 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.