Four reactive flow-through laboratory experiments (two each at 0.1 mL/min and 0.01 mL/min flow rates) at 150°C and 150 bar (15 MPa) are conducted on intact basalt cores to assess changes in porosity, permeability, and surface area caused by CO2-rich fluid-rock interaction. Permeability decreases slightly during the lower flow rate experiments and increases during the higher flow rate experiments. At the higher flow rate, core permeability increases by more than one order of magnitude in one experiment and less than a factor of two in the other due to differences in preexisting flow path structure. X-ray computed tomography (XRCT) scans of pre- and post-experiment cores identify both mineral dissolution and secondary mineralization, with a net decrease in XRCT porosity of ∼0.7%–0.8% for the larger pores in all four cores. (Ultra) small-angle neutron scattering ((U)SANS) data sets indicate an increase in both (U)SANS porosity and specific surface area (SSA) over the ∼1 nm to 10 µm scale range in post-experiment basalt samples, with differences due to flow rate and reaction time. Net porosity increases from summing porosity changes from XRCT and (U)SANS analyses are consistent with core mass decreases. (U)SANS data suggest an overall preservation of the pore structure with no change in mineral surface roughness from reaction, and the pore structure is unique in comparison to previously published basalt analyses. Together, these data sets illustrate changes in physical parameters that arise due to fluid-basalt interaction in relatively low pH environments with elevated CO2 concentration, with significant implications for flow, transport, and reaction through geologic formations.
Bibliographical noteFunding Information:
We thank Travis McLing from the Idaho National Laboratory for providing the basalt borehole sample and the Micromeritics Analytical Services Lab in Norcross, GA, USA for the BET SSA measurement. XRCT data and images were produced at the X-ray Computed Tomography Laboratory in the Department of Earth Sciences, University of Minnesota (UMN), which was funded by a UMN Infrastructure Investment Initiative Grant. The small-angle neutron scattering instruments at the National Institute of Standards and Technology were supported in part by the National Science Foundation under agreement DMR-0944772. The identification of commercial products in this paper does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the equipment used are necessarily the best available for the purpose. Research support was provided by the Initiative for Renewable Energy and the Environment, a signature program of the Institute on the Environment at UMN, the US 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. The Supporting Information (Data Sets S1?S3) provides permeability, XRCT, and (U)SANS data in Microsoft Excel spreadsheets. The critical evaluation provided by Associate Editor Russ Detwiler and three anonymous reviewers has improved the impact and clarity of our manuscript.
- (ultra) small-angle neutron scattering ((U)SANS)
- X-ray computed tomography (XRCT)
- reactive transport
- surface area