Significance of carbonate buffers in natural waters reacting with supercritical CO2: Implications for monitoring, measuring and verification (MMV) of geologic carbon sequestration

[1] Successful geologic sequestration of carbon in deep saline aquifers requires accurate predictive models of rock-brine-CO2 interaction. Often overlooked in siliciclastichosted saline reservoirs is the carbonate buffering of the groundwater. Carbonate minerals are ubiquitous, even in siliciclastic host rocks, resulting in some carbonate buffering. Geochemical modeling of rock-brine-CO2 systems often do not accurately predict the geochemical evolution of the system leading to significant doubts in predicting the performance of carbon repositories. New data from a simple NaCl brine-plagioclase hydrothermal experiment tests carbon sequestration in dawsonite and sensitivity to carbonate buffering. This is contrasted to a NaCl brine siliciclastic rock system containing some initial bicarbonate buffering, analogous to most saline-aquifer sequestration targets, and show that critical errors are caused by incomplete or inaccurate characterization of the in situ geochemistry. We provide a methodology that accurately predicts the in situ condition using samples collected from brine-rock-CO2 experiments or well-heads in a carbon sequestration monitoring scenario. Citation: Newell, D. L., J. P. Kaszuba, H. S. Viswanathan, R. J. Pawar, and T. Carpenter (2008), Significance of carbonate buffers in natural waters reacting with supercritical CO2: Implications for monitoring, measuring and verification (MMV) of geologic carbon sequestration, Geophys. Res. Lett., 35, L23403, doi:10.1029/ 2008GL035615.