Abstract
We developed an integrated framework of combined batch experiments and reactive transport simulations to quantify water-rock-CO2 interactions and arsenic (As) mobilization responses to CO2 and/or saline water leakage into USDWs. Experimental and simulation results suggest that when CO2 is introduced, pH drops immediately that initiates release of As from clay minerals. Calcite dissolution can increase pH slightly and cause As re-adsorption. Thus, the mineralogy of the USDW is ultimately a determining factor of arsenic fate and transport. Salient results suggest that: (1) As desorption/adsorption from/onto clay minerals is the major reaction controlling its mobilization, and clay minerals could mitigate As mobilization with surface complexation reactions; (2) dissolution of available calcite plays a critical role in buffering pH; (3) high salinity in general hinders As release from minerals; and (4) the magnitude and quantitative uncertainty of As mobilization are predicated on the values of reaction rates and surface area of calcite, adsorption surface areas and equilibrium constants of clay minerals, and cation exchange capacity. Results of this study are intended to improve ability to quantify risks associated with potential leakage of reservoir fluids into shallow aquifers, in particular the possible environmental impacts of As mobilization at carbon sequestration sites.
Highlights
Geologic CO2 sequestration (GCS) is considered a promising approach for mitigating CO2 emissions from centralized sources[1,2,3,4,5,6,7,8,9]
Most of these studies focus on CO2 leakage and its impacts on groundwater quality, but a limited number of studies have examined the leakage of brine with/without CO2 into shallow aquifers
To date, modeling approaches combined with laboratory/field observations are necessary for studies of the geochemical impacts of leaked CO2 in shallow aquifers, to reduce the uncertainties of modeling itself and to interpret the observation data with appropriate reaction patterns
Summary
Geologic CO2 sequestration (GCS) is considered a promising approach for mitigating CO2 emissions from centralized sources[1,2,3,4,5,6,7,8,9]. To assess the risk of CO2/brine leakage to overlying USDWs and to detect signatures of aquifer quality changes at early stages, various approaches have been conducted with lab-scale experiments[11, 15,16,17], short-term field-scale tests[18,19,20], numerical modeling[21,22,23,24,25,26,27], and natural analog observations[13, 28]. A specific objective for this study is to identify the responses of As release under different water salinities and to quantify the key parameters controlling As mobilization processes
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