Geochemical Impacts to Groundwater from Geologic Carbon Sequestration: Controls on pH and Inorganic Carbon Concentrations from Reaction Path and Kinetic Modeling

Abstract

Geologic carbon sequestration has the potential to cause long-term reductions in global emissions of carbon dioxide to the atmosphere. Safe and effective application of carbon sequestration technology requires an understanding of the potential risks to the quality of underground sources of drinking water. In particular, concern is warranted regarding the potential for CO(2) leakage through geological features and abandoned wells that may result in detrimental perturbations to subsurface geochemistry. Reaction path and kinetic models indicate that geochemical shifts caused by CO(2) leakage are closely linked to mineralogical properties of the receiving aquifer. CO(2) gas dissolution into groundwater and subsequent reaction with aquifer minerals will control the evolution of pH-bicarbonate envelopes. These parameters provide geochemical context for predicting how regulated contaminants associated with aquifer solids will respond via various mineral-water reaction processes. The distribution and abundance of carbonate, silicate, oxide, and phyllosilicate minerals are identified as key variables in controlling changes in groundwater geochemistry. Site-specific risk assessments may require characterization of aquifer geology, mineralogy, and groundwater chemistry prior to CO(2) injection. Model results also provide a frame of reference for developing indicative measurement, monitoring, and verification (MMV) protocols for groundwater protection.

Developing a robust geochemical and reactive transport model to evaluate possible sources of arsenic at the CO2 sequestration natural analog site in Chimayo, New Mexico

“…For time points where the pH decreases from ∼8 to ∼6, aqueous As also is observed to decrease slightly from 0.020 mg/L to 0.017 mg/L (within 0.04 days), however pH slowly increases after the initial drop throughout the remainder of the experiment while As concentrations continue to decrease. Wilken and Digiulio (2010) notes that anionic metalloids such as As may be more effectively sorbed at lower pH; which is generally consistent with our experimental and modeling trends. Additionally, as the pH decreases and H + concentration increases due to the introduction of CO 2 , our model shows that precipitation of clay minerals (e.g.…”

On modeling the potential impacts of CO2 sequestration on shallow groundwater: Transport of organics and co-injected H2S by supercritical CO2 to shallow aquifers

“…First, the dissolution of CO 2 in water increases the concentration of dissolved carbonic acid and thus increases acidity, which could mobilize trace elements through mineral dissolution, desorption reactions, and/or exchange reactions involving H + and other mobilized 3 constituents (e.g., Aiuppa et al, 2005;Zheng et al, 2009;Kharaka et al, 2010;Little and Jackson, 2010;Wilkin and Digiulio, 2010;Zheng et al, 2012;Trautz et al, 2012). In addition, the increased dissolved CO 2 concentrations could result in desorption of metals such as arsenic by competitive sorption of carbonate ions (Appelo et al, 2002).…”

Phase II Final Scientific/Technical Report

“…Overall, these geochemical covariations suggest that small amounts of carbonate in an aquifer (1 to 5 % in this case) may yield a geochemistry receptive to changes in CO 2 , supporting the hypothesis that carbonate parameters may be useful indicators of leakage. This conclusion is in direct opposition to the assumption of Wilkin and Digiulio (2010) who argue that a quartz-rich aquifer would be non-reactive. The suggestion is that variable amounts of mixing of Dockum water with Permian and coproduced brines affect the geochemistry of the Dockum at SACROC.…”