Geochemical dynamics of Bravo Dome natural CO₂ field




Sathaye, Kiran Jayant

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This dissertation combines geophysical and geochemical data from the Bravo Dome natural CO₂ field, analytical and numerical modeling, and two-phase experiments to investigate the compositional changes which occur during gas migration through groundwater in sedimentary systems. First, a detailed reservoir model of the Bravo Dome natural CO₂ reservoir is used to determine that roughly half of the magmatic CO₂ in this reservoir which has been dissolved into an aqueous phase dissolved during emplacement. Furthermore, only 22% of the total CO₂ has dissolved into the underlying brine in 1.2Ma since the CO₂ emplacement. This result shows the importance of CO₂ dissolution trapping during injection, and the difficulty of convective dissolution of ponded gaseous CO₂ in saline aquifers. The Bravo Dome reservoir model also provides estimates of various noble gas isotope totals, which show that tectonically stable continental crust is retentive of noble gases, and that the CO₂ entry event mobilized radiogenic gases which were previously trapped in deep crustal grain boundaries. An experimentally verified mathematical model for the chromatographic separation of trace gas components explains many of the noble gas isotope gradients observed at Bravo Dome, and in shallow groundwater aquifers in shale gas producing regions.


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