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Despite the numerous studies on changes within the reservoir following CO 2 injection and the effects of CO 2 release into overlying aquifers, little or no literature is available on the effect of CO 2 release on rock between the storage reservoirs and subsurface. This is important, because the interactions that occur in this zone between the CO 2 storage reservoir and the subsurface may have a significant impact on risk analysis for CO 2 storage projects. To address this knowledge gap, relevant rock materials, temperatures and pressures were used to study mineralogical and elemental changes in this intermediate zone. After rocks reacted with CO 2 -acidified 0.01 M NaCl, liquid analysis showed an increase of major elements (e.g., Ca and Mg) and variable concentrations of potential contaminants (e.g., Sr and Ba); lower aqueous concentrations of these elements were observed in N 2 control experiments, likely due to differences in pH between the CO 2 and N 2 experiments. In experiments with As/Cd and/or organic spikes, representing potential contaminants in the CO 2 plume originating in the storage reservoir, most or all of these contaminants were removed from the aqueous phase. SEM and Mössbauer spectroscopy results showed the formation of new minerals and Fe oxides in some CO 2 -reacted samples, indicating potential for contaminant removal through mineral incorporation or adsorption onto Fe oxides. These experiments show the interactions between the CO 2 -laden plume and the rock between storage reservoirs and overlying aquifers have the potential to affect the level of risk to overlying groundwater, and should be considered during site selection and risk evaluation., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This paper demonstrates an approach to identify optimal monitoring designs that minimize the time to first detection of CO 2 leakage from a subsurface storage formation. This research is part of the National Risk Assessment Partnership (NRAP), a DOE project tasked with conducting risk and uncertainty analysis in the areas of reservoir performance, natural leakage pathways, wellbore integrity, groundwater protection, monitoring, and systems level modeling. Our approach applies a simulated annealing algorithm that searches the solution space by iteratively mutating potential monitoring designs. A user-defined leakage signature based on change from initial conditions is implemented to infer CO 2 leakage had occurred. An example application was performed to demonstrate the effectiveness and efficiency of this method compared to an exhaustive search of the entire solution space. We accounted for uncertainty in the example by evaluating the performance of potential monitoring designs across a set of simulated leakage realizations. The example application approached the optimal time to leakage detection in a few minutes using a standard workstation, which was several orders of magnitude faster than an exhaustive search of the solution space, thus exhibiting efficiency and effectiveness. A user-friendly tool, DREAM (Designs for Risk Evaluation and Management), is being developed for use on personal computers to make this method accessible to stakeholders, regulators, and researchers. [ABSTRACT FROM AUTHOR]

Multiphase, reactive transport modeling was used to identify the mechanisms controlling trace metal release under elevated CO 2 conditions from a well-characterized carbonate aquifer. Modeling was conducted for both batch and column experiments. The column experiments resulted in higher trace metal concentrations because the rock to water ratio was higher. A kinetic desorption model fits the overall trends in release for seven trace metals observed in batch and column experiments exposing Edwards Aquifer material to elevated concentrations of CO 2 . Observed and predicted trace metal concentrations are compared to groundwater concentrations from this aquifer to determine the potential for leaking CO 2 to adversely impact drinking water quality. Finally, a three-dimensional multiphase flow and reactive-transport simulation of CO 2 leakage from an abandoned wellbore into a generalized model of the shallow, unconfined portion of the aquifer is used to determine potential impacts on groundwater quality. As a measure of adverse impacts on groundwater quality, both the EPA’s regulatory limits and the maximum trace metal concentration observed in the aquifer were used as threshold values. Results of the field-scale simulations indicate that CO 2 leakage into a carbonate aquifer is likely to cause decreases in pH and increases in TDS beyond observed ranges in the aquifer and beyond regulatory limits. However, trace metal concentrations are not predicted to exceed either the observed maximums or the regulatory limits. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mineral sequestration of CO2 in Columbia River Basalt under field conditions is predicted to occur within several decades. [•] Mineral sequestration of co-injected H2S is predicted to occur within several years. [•] Modeled rates are consistent with laboratory predictions. [•] Binary interaction parameters for the solubility of CO2 and H2S in pure water and brine are detailed. [Copyright &y& Elsevier]

Abstract: Geochemical simulations indicate that co-injection of CO2 and SO2 results in mineral sequestration of SO2. The amounts sequestered are greater and more persistent in dolomite and basalt than in glauconitic sandstone. In a predominantly dolomite formation, dissolution of calcite, and to a lesser extent, dolomite, will provide Ca in solution to promote the precipitation of anhydrite, thus removing the SO2 from solution. In basalt, dissolution of basaltic glass under acidic conditions provides Ca and Fe in solution, which promotes the sequestration of SO2 as anhydrite and, eventually, pyrite. As magnetite in the formation is consumed, pyrite redissolves. In the basalt, 86% to 47% of the SO2 remains sequestered after 5000 years. In glauconitic sandstone, SO2 precipitates as alunite, but it eventually redissolves. After 5000 years, 87% to 0% of the SO2 remains sequestered in the glauconitic sandstone. In all cases, co-injection of 1% SO2 with CO2 did not appreciably reduce the amount of CO2 sequestered, and did not induce a measureable change in porosity versus injection of CO2 alone. [Copyright &y& Elsevier]

Abstract: Injection of supercritical carbon dioxide (CO2) into formations containing carbonate minerals may affect the porosity and permeability of the host rock and overlying caprock due to dissolution of the primary carbonate minerals and possible precipitation of secondary minerals. Simulations of pilot-scale CO2 injection with co-sequestration of sulfur dioxide (SO2) were conducted to assess the competing effects of dolomite dissolution and anhydrite precipitation on formation hydraulic properties. A geochemical model of two promising host formations in the midwestern United States (Rose Run and Copper Ridge) was developed for the purpose of assessing mineral dissolution and precipitation effects on injectivity and containment. [Copyright &y& Elsevier]