To investigate CO2 Capture, Utilization, and Storage (CCUS) in sandstones, we performed three 150°C flow-through experiments on K-feldspar-rich cores from the Eau Claire formation. By characterizing fluid and solid samples from these experiments using a suite of analytical techniques, we explored the coupled evolution of fluid chemistry, mineral reaction rates, and hydrogeochemical properties during CO2 sequestration in feldspar-rich sandstone. Overall, our results confirm predictions that the heightened acidity resulting from supercritical CO2 injection into feldspar-rich sandstone will dissolve primary feldspars and precipitate secondary aluminum minerals. A core through which CO2-rich deionized water was recycled for 52days decreased in bulk permeability, exhibited generally low porosity associated with high surface area in post-experiment core sub-samples, and produced an Al hydroxide secondary mineral, such as boehmite. However, two samples subjected to ~3day single-pass experiments run with CO2-rich, 0.94mol/kg NaCl brines decreased in bulk permeability, showed generally elevated porosity associated with elevated surface area in post-experiment core sub-samples, and produced a phase with kaolinite-like stoichiometry. CO2-induced metal mobilization during the experiments was relatively minor and likely related to Ca mineral dissolution. Based on the relatively rapid approach to equilibrium, the relatively slow near-equilibrium reaction rates, and the minor magnitudes of permeability changes in these experiments, we conclude that CCUS systems with projected lifetimes of several decades are geochemically feasible in the feldspar-rich sandstone end-member examined here. Additionally, the observation that K-feldspar dissolution rates calculated from our whole-rock experiments are in good agreement with literature parameterizations suggests that the latter can be utilized to model CCUS in K-feldspar-rich sandstone. Finally, by performing a number of reactive transport modeling experiments to explore processes occurring during the flow-through experiments, we have found that the overall progress of feldspar hydrolysis is negligibly affected by quartz dissolution, but significantly impacted by the rates of secondary mineral precipitation and their effect on feldspar saturation state. The observations produced here are critical to the development of models of CCUS operations, yet more work, particularly in the quantification of coupled dissolution and precipitation processes, will be required in order to produce models that can accurately predict the behavior of these systems.
Bibliographical noteFunding Information:
We gratefully acknowledge support from the Department of Energy ( DOE ) Geothermal Technologies Program under Grant Number EE0002764 and from the Initiative for Renewable Energy and the Environment ( IREE ), a signature program of the Institute on the Environment (IonE) at the University of Minnesota (UMN) for this contribution and related research. XPS analyses were carried out by Dr. Bing Luo and SEM images were obtained by Nick Seaton, both of whom are part of the UMN Characterization Facility, which receives partial support from NSF through the MRSEC program. Kevin Roberts of the UMN Nanofabrication Center assisted with the FIB-SEM analyses, and Rick Knurr performed the ICP-OES and IC analyses. Use of the Advanced Photon Source (APS) was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. We are grateful to beamline scientist Dr. Xianghui Xiao for assistance with APS tomographic data, Glenn Hammond of Sandia National Laboratories for his assistance with PFLOTRAN applications, and Anthony Runkel of the Minnesota Geological Survey for providing the sandstone samples. XRCT data processing and PFLOTRAN simulations were carried out in part using computing resources and software at the University of Minnesota Supercomputing Institute and software available through the UMN XRCT Laboratory. WES would like to acknowledge support from NSF MGG-OCE under grant numbers 0927615, 1232704, and 1426695 for this contribution and related research. MOS also acknowledges support for this and related research from an NSF Sustainable Energy Pathways (SEP) grant, NSF SEP-1230691, and is grateful for the support of the Hydrogeology and Geofluids research group by the George and Orpha Gibson Endowment. BMT would also like to acknowledge the organizers and attendees of the NSF “Expanding the Role of Reactive Transport Models (RTMs) in the Biogeochemical Sciences” workshop for their interesting discussions of the data needs for successful application of RTMs. Any opinions, findings, conclusions, or recommendations in this material are those of the authors and do not necessarily reflect the views of the DOE, NSF, IREE, IonE, UMN, or ETH. The authors thank Associate Editor Carl Steefel, Nicholas Pester (LBNL), and two anonymous reviewers for their thorough, thoughtful reviews of this manuscript, which significantly improved its clarity and strengthened its impact.