| Description |
Geologic CO2 sequestration (GCS) is believed to play a critical role for mitigating CO2 emissions. Many geologic carbon storage site options include not only excellent storage reservoirs bounded by effective seal layers, but also Underground Sources of Drinking Water (USDWs). An effective risk assessment of potential CO2 leakage from the reservoirs provides maximum protection for USDWs. A primary purpose of this dissertation is to quantify possible risks of CO2 leakage to USDWs, specifically risks associated with chemical impacts. Wellbore provides possible leakage pathways for CO2, and its integrity is a key risk factor for geological CO2 storage. This dissertation firstly presents an analysis on the impacts of CO2 leakage through wellbore cement and surrounding caprock with a gap (annulus) in between. Mechanisms of chemical reactions associated with cement-CO2-brine interactions are predicted, and wellbore integrity under CO2-rich conditions is analyzed with a case study example â€" the Farnsworth CO2 enhanced oil recovery (EOR) unit (FWU) in the northern Anadarko Basin in Texas. The second part of this dissertation focuses on quantification of possible risks of CO2 leakage through fractured wellbores to overlying USDWs. To understand how CO2 is likely to influence geochemical processes in aquifer sediments, a response surface methodology (RSM) with geochemical simulations is used to quantify associated risks. The case study example for this analysis is the Ogallala aquifer overlying the FWU. Increased CO2 concentrations in shallow groundwater aquifers could result in release and mobilization of toxic trace metals. This dissertation also presents an integrated framework of combined batch experiments and reactive transport simulations to quantify trace metal mobilization responses to CO2 leakage into USDWs. The mechanisms of trace metal mobilization are elucidated, and the key parameters are quantified. The case study includes elevated CO2 conditions at the Chimayo site in northern New Mexico, a natural analog with CO2 upwelling. |
