Constraints on the magnitude and rate of CO₂ dissolution at Bravo Dome natural gas field
2014
Sathaye, Kiran J. | Hesse, Marc A. | Cassidy, Martin | Stockli, Daniel F.
The injection of carbon dioxide (CO ₂) captured at large point sources into deep saline aquifers can significantly reduce anthropogenic CO ₂ emissions from fossil fuels. Dissolution of the injected CO ₂ into the formation brine is a trapping mechanism that helps to ensure the long-term security of geological CO ₂ storage. We use thermochronology to estimate the timing of CO ₂ emplacement at Bravo Dome, a large natural CO ₂ field at a depth of 700 m in New Mexico. Together with estimates of the total mass loss from the field we present, to our knowledge, the first constraints on the magnitude, mechanisms, and rates of CO ₂ dissolution on millennial timescales. Apatite (U-Th)/He thermochronology records heating of the Bravo Dome reservoir due to the emplacement of hot volcanic gases 1.2–1.5 Ma. The CO ₂ accumulation is therefore significantly older than previous estimates of 10 ka, which demonstrates that safe long-term geological CO ₂ storage is possible. Integrating geophysical and geochemical data, we estimate that 1.3 Gt CO ₂ are currently stored at Bravo Dome, but that only 22% of the emplaced CO ₂ has dissolved into the brine over 1.2 My. Roughly 40% of the dissolution occurred during the emplacement. The CO ₂ dissolved after emplacement exceeds the amount expected from diffusion and provides field evidence for convective dissolution with a rate of 0.1 g/(m ²y). The similarity between Bravo Dome and major US saline aquifers suggests that significant amounts of CO ₂ are likely to dissolve during injection at US storage sites, but that convective dissolution is unlikely to trap all injected CO ₂ on the 10-ky timescale typically considered for storage projects.
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