Under-pressure in the Bravo Dome natural CO₂ field and its implications for geological CO₂ storage (GCS)

Geological carbon storage (GCS) has the potential to reduce anthropogenic CO₂ emissions, if large volumes can be injected. Storage capacity is limited by regional pressure build-up in the subsurface. However, natural CO₂ reservoirs are commonly under-pressured, suggesting that natural processes counteract the pressure build-up and increase storage security. To identifythese processes, I studied Bravo Dome natural CO₂ reservoir, where the gas pressure are significantly below hydrostatic pressure. Here, I showed that the dissolution of CO₂ into the brine contributes to observed under-pressure conditions because Bravo Dome appears to be isolated from the ambient hydrologic system. This study indicated that the pressure drop in the gas due to CO₂ dissolution slows down convective dissolution dramatically. I present 2D numerical simulations and reproduce the observed reservoir pressures and noble gas compositions. Based on this study, CO₂ at Bravo Dome must at least persist for 300 ka to produce the observed noble gas composition and reservoir pressures. Lastly, I showed that compartmental gas pressure observed at Bravo Dome are controlled by capillary forces.