Four flow-through experiments at 150 °C were conducted on intact cores of basalt to assess alteration and mass transfer during reaction with CO2-rich fluid. Two experiments used a flow rate of 0.1 ml/min, and two used a flow rate of 0.01 ml/min. Permeability increased for both experiments at the higher flow rate, but decreased for the lower flow rate experiments. The experimental fluid (initial pH of 3.3) became enriched in Si, Mg, and Fe upon passing through the cores, primarily from olivine and titanomagnetite dissolution and possibly pyroxene dissolution. Secondary minerals enriched in Al and Si were present on post-experimental cores, and an Fe2O3-rich phase was identified on the downstream ends of the cores from the experiments at the lower flow rate. While we could not specifically identify if siderite (FeCO3) was present in the post-experimental basalt cores, siderite was generally saturated or supersaturated in outlet fluid samples, suggesting a thermodynamic drive for Fe carbonation from basalt-H2O-CO2 reaction. Reaction path models that employ dissolution kinetics of olivine, labradorite, and enstatite also suggest siderite formation at low pH. Furthermore, fluid-rock interaction caused a relatively high mobility of the alkali metals; up to 29% and 99% of the K and Cs present in the core, respectively, were preferentially dissolved from the cores, likely due to fractional crystallization effects that made alkali metals highly accessible. Together, these datasets illustrate changes in chemical parameters that arise due to fluid-basalt interaction in relatively low pH environments with elevated CO2.
Bibliographical noteFunding Information:
We thank Travis McLing from the Idaho National Laboratory for providing the basalt borehole sample, Rick Knurr for fluid and rock analyses, Nick Seaton for SEM pictures and analyses, and Anette von der Handt for the electron microprobe analyses. We also thank an anonymous reviewer for a thorough review that strengthened this manuscript. The SEM image in Fig. 7a was collected at LacCore, University of Minnesota. SEM images in Fig. 6 were taken in the Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the MRSEC program. The Institute for Rock Magnetism is supported by grants from the Instruments and Facilities Program, Division of Earth Science, National Science Foundation. Research support was provided by the Initiative for Renewable Energy and the Environment, a signature program of the Institute on the Environment at the University of Minnesota, the U.S. Department of Energy Geothermal Technologies Program through Grant DE-EE0002764, and the National Science Foundation through Grant OCE 1426695. M.O.S. also thanks the George and Orpha Gibson Endowment for its support of the Hydrogeology and Geofluids Research Group at the University of Minnesota and the Werner Siemens Stiftung/Endowment for its support of the Geothermal Energy and Geofluids Group at ETH-Zurich, Switzerland.
- Basalt alteration
- Carbon sequestration
- Fluid-rock reaction
- Olivine dissolution
- Reactive transport