Reactive Transport Simulations to Study Groundwater Quality Changes in Response to CO_2 Leakage from Deep Geological Storage

摘要

As an effort to evaluate risks associated with geologic sequestration of CO_2, this work assesses the potential effects of CO_2 leakage on groundwater quality. Reactive transport simulations are performed to study the chemical evolution of aqueous Pb and As after the intrusion of CO_2 from a storage reservoir into a shallow confined groundwater resource. The simulations use mineralogies representative of shallow potable aquifers in the USA; both 2D (depth-averaged) and 3D simulations are conducted. Sensitivity studies are also conducted for variation in hydrological and geochemical conditions, as well as several other critical parameters. Model results suggest that a significant increase of aqueous lead (Pb) and arsenic (As) may occur in response to CO_2 intrusion, but in most sensitivity cases their concentrations remain below the EPA specified maximum contaminant levels (MCLs). Adsorption/desorption from mineral surfaces significantly impacts the mobilization of Pb and As. Results from the 3D model agree fairly well with the 2D model in cases where the rate of CO_2 intrusion is relatively small (so that the majority of CO_2 readily dissolves in the groundwater), whereas discrepancies between 2D and 3D models are observed when the CO_2 intrusion rate is comparably large.