Modeling CO2 migration in a site-specific shallow subsurface under complex hydrodynamics

Abstract

Potential pathways in the subsurface may allow upward migrating CO2 from deep geological storage reservoirs into shallow subsurface aquifers. Detailed simulations of CO2 migration in the near surface are necessary for monitoring design where the near-surface groundwater flow field is usually complicated by rainfall and pumping wells. This work studied the CO2 migration under complex hydrodynamic conditions by numerical simulation for a specific site. Results shows that in a coupled soil and aquifer formation, the leakage rate of CO2 dominates the whole migration process, especially in the vadose zone. The groundwater velocity determines the lateral distance of CO2 migration with the groundwater flow, and simultaneously weakens the upward migration trend. Under certain conditions, such as the leakage rate of 1 × 10−5 kg/s and the groundwater velocity of 6.7 × 10−8 m/s, upward migration of CO2 is completely suppressed, therefore it will not leak to the surface. Both rainfall and pumping wells affect the migration indirectly by changing the groundwater flow field, while the impact of the latter is greater. When the well extraction increases or the well is downstream of the leak, CO2 will be extracted to the well. The permeability heterogeneity will also promote migration. Complex groundwater environments require more attention in the monitoring work.