Impacts of elevated dissolved CO₂ on a shallow groundwater system: Reactive transport modeling of a controlled-release field test

Journal Article · Sat Oct 22 04:00:00 EDT 2016 · Chemical Geology

DOI:https://doi.org/10.1016/j.chemgeo.2016.10.027· OSTI ID:1474989

Zheng, Liange ^[1]; Spycher, Nicolas ^[1]; Bianchi, Marco ^[2]; Pugh, John D. ^[3]; Varadharajan, Charuleka ^[1]; Tinnacher, Ruth M. ^[1]; Birkholzer, Jens T. ^[1]; Nico, Peter ^[1]; Trautz, Robert C. ^[4]

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1. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
2. British Geological Survey, Keyworth, Nottingham (United Kingdom)
3. Southern Company Services, Birmingham, AL (United States)
4. Electric Power Research Institute, Palo Alto, CA (United States)

We report one of the risks that CO₂ geological sequestration imposes on the environment is the impact of potential CO₂ /brine leakage on shallow groundwater. The reliability of reactive transport models predicting the response of groundwater to CO₂ leakage depends on a thorough understanding of the relevant chemical processes and key parameters affecting dissolved CO₂ transport and reaction. Such understanding can be provided by targeted field tests integrated with reactive transport modeling. A controlled-release field experiment was conducted in Mississippi to study the CO₂-induced geochemical changes in a shallow sandy aquifer at about 50 m depth. The field test involved a dipole system in which the groundwater was pumped from one well, saturated with CO₂ at the pressure corresponding to the hydraulic pressure of the aquifer, and then re-injected into the same aquifer using a second well. Groundwater samples were collected for chemical analyses from four monitoring wells before, during and after the dissolved CO₂ was injected. In this paper, we present reactive transport models used to interpret the observed changes in metal concentrations in these groundwater samples. A reasonable agreement between simulated and measured concentrations indicates that the chemical response in the aquifer can be interpreted using a conceptual model that encompasses two main features: (a) a fast-reacting but limited pool of reactive minerals that responds quickly to changes in pH and causes a pulse-like concentration change, and (b) a slow-reacting but essentially unlimited mineral pool that yields rising metal concentrations upon decreased groundwater velocities after pumping and injection stopped. During the injection, calcite dissolution and Ca-driven cation exchange reactions contribute to a sharp pulse in concentrations of Ca, Ba, Mg, Mn, K, Li, Na and Sr, whereas desorption reactions control a similar increase in Fe concentrations. Finally, after the injection and pumping stops and the groundwater flow rate decreases, the dissolution of relatively slow reacting minerals such as plagioclase drives the rising concentrations of alkali and alkaline earth metals observed at later stages of the test, whereas the dissolution of amorphous iron sulfide causes slowly increasing Fe concentrations.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Fossil Energy (FE)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1474989
• Alternate ID(s): OSTI ID: 1411089
• Journal Information: Chemical Geology, Journal Name: Chemical Geology Journal Issue: C Vol. 447; ISSN 0009-2541
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES