Extensive CO2 Leakage From Extinct and Modern CO2 Reservoirs in New Mexico and Arizona: Evaluating the Role of Seal Bypass and Large-Volume Travertine Deposition With Implications For CO2 Sequestration

Abstract:

Quaternary large-volume travertine deposits in New Mexico and Arizona occur along the Rio Grande rift and on the southeastern Colorado Plateau. Travertines are natural analogues for CO₂ leakage along fault systems because they form due to the degassing of CO₂ from carbonic groundwater that migrates up fault systems. Travertine volumes can be used to infer integrated CO₂ leakage along faults, which includes: (1) CO₂ that becomes fixed in CaCO₃/travertine (tons of carbon converted into tons of carbonate), (2) the amount of CO₂ that degassed into the atmosphere (twice the amount of (1), based on reaction stoichiometry), (3) dissolved CO₂ that is carried away with the water discharging from a spring (based on modern spring discharge and dissolved carbon content), and (4) CO₂ that escapes through the soil (based on modern soil flux measurements). The total CO₂ leakage (1 and 2) calculated in this study is estimated as ~6 Gt (gigatons) whereas the integrated CO₂ leakage (1-4) is estimated as ~128 Gt over ~450,000 years of travertine accumulation. U-series dating of the travertines shows that the deposits formed episodically which implies that CO₂ leakage occurred episodically. Better understanding of integrated CO₂ leakage along fault systems is needed to better constrain global estimates of natural CO₂ fluxes, and to help in risk assessment of CO₂ sequestration sites designed to effectively store anthropogenic CO₂ in the subsurface.