Impact of a CO2 leakage on groundwater quality. Influence of regional flow using reactive transport models.

摘要

Carbon Capture and Storage in deep and saline aquifers is one of the most hopeful technologies to reduce CO2 emissions into the atmosphere. However, CO2 leakages into shallow freshwater aquifers are a potential risk and potential impacts on groundwater have to be studied. A better understanding on how it could affect groundwater quality, aquifer minerals and trace elements is necessary to characterize a future storage site. Moreover, monitoring and remediation solutions have to be evaluated before storage operations. As part of the ANR project CIPRES, we present here reactive transport works. In a 3D model using ToughReact2, we perform different CO2 leakage scenarios in a confined aquifer, considering both brines and carbon dioxide gas. Our modeling works are based on the Albian aquifer, a strategic water resource for the Paris basin. This layer is the main aquifer overlying the Dogger deep saline aquifer. We consider one groundwater and rocks chemistry of the Albian aquifer composed by the Albian green sand (Quartz, Calcite, Glauconite , Kaolinite) at 700 m deep. The geochemical model was elaborated from experimental data performed in previous study (Humez, 2012). The aquifer consists in a mesh, divided roughly in 20000 cells making a 60 m thick and a 500 m large layer. Furthermore, cells are subdivided near the leakage point to consider local phenomena (secondary precipitation, kinetics, sorption/desorption...). We highlight the importance of surface complexation on trace element transport (As, Zn and Ni). Moreover, we distinguish different geochemical behavior (CO2 plume shape, secondary precipitation of siderite or chalcedony, desorption...) according to different horizontal flow rate influenced directly by the hydrodynamics (regional gradient). Understanding how geochemical reactions and regional flows influence water chemistry, allows to ascertain measurement monitoring and verification plan and remediation works in case of leak considering a given location.