Gigaton Commercial-Scale Carbon Storage and Mineralization Potential in Stacked Columbia River Basalt Reservoirs

: We present a detailed supercritical CO 2 storage resource estimation for the stacked interflow reservoirs in the 12 Grande Ronde Basalt of the Columbia River Basalt Group. This study aims to parametrize subsurface, economic, and 13 regulatory analyses needed to derisk and commercialize geologic carbon storage in continental flood basalts, including in 14 the doubly plunging anticlinal traps of the Yakima Fold Belt in our study area while leveraging rapid mineralization trapping 15 of injected CO 2 in basalt. The structural closures formed by anticlinal ridges and synclinal valleys in the Yakima Fold Belt 16 provide excellent physical traps to accommodate injected supercritical CO 2 and allow for injection at supercritical conditions 17 (depths >800 m). We analyzed deep borehole well logs, structural maps, hydrologic test results, and numerical simulations 18 to calculate carbon storage resource for our study area of SE Washington and NE Oregon. Hydrologic testing, well log, and 19 reactive transport simulations from the Wallula Basalt Pilot #1 well provided data for 17 permeable injection zones (~500-20 2500 mD) separated by impermeable aquitards (~2.6E-10 mD) in the Grande Ronde Basalt. This investigation highlights a 21 highly secure pathway to permanent geological CO 2 storage for up to 181, 304, or 351 gigatons (P90, P50, and P10,

To demonstrate that the wells will be sited in areas with a suitable geologic storage system, the basaltic storage complex need to comprise:

METHODS
To estimate the carbon storage potential in southern Columbia Basin and YFB, we analyzed three key deep boreholes in the region.The study area (~88,000 km 2 ) is shown in Figure 2 and was chosen for analysis due to the availability of subsurface data and favorable geologic structures.The isochore thickness of GRB storage complex in the study area ranges from 1,500-3,250 m and is characterized as dozens of stacked flow members.
There are 19 GRB members present in the study area, comprising at least 90 individual flows (Figure S1).
Individual flow thicknesses range from a few meters to more than 100 m, with an average of ~30 m.Greatest flow thicknesses, ~100 m, are found in the central Columbia Basin (Figure 2) 43 .GRB members share relatively homogeneous bulk lithology and are chemically coherent 44 , but vary dramatically in extent and volume 43 .We discuss the properties of each member encountered in the key wells in Figure 3.
We integrated subsurface data from three boreholes in the study area to investigate the reservoir and seal properties of the GRB (Figure 2).Wallula Basalt Pilot #1, drilled in 2009, is the first and only well to host pilot-scale supercritical CO2 injection into basalt; 100 Circles #1, drilled in 1999, was a reservoir characterization well that suggested favorable conditions for natural gas storage in basalt 42 ; and K2H #1 was also a natural gas storage characterization well drilled in 1999 with limited data available.The geophysical wireline logs for the three boreholes used in our resource estimate are summarized in Table S1 and were used to differentiate basalt members and characterize storage potential in the GRB.We adopted the US-DOE methodology to estimate the carbon storage resource of the GRB in the study area in an open system 45 .The volumetric results (GCO2) are calculated for low, medium, and high probability of storage resource potential; P10, P50, and P90, respectively.We used the broadly applicable coefficients 46 for effective storage resource estimates in saline formations.The volumetric approach is based on the reservoir's physical geometry, fluid properties, geologic heterogeneity, buoyancy effects and sweep efficiency.As no previous study to our knowledge has reported storage potential coefficients for basaltic reservoirs, we approximated the storage coefficients (Table S3      Supporting Information.General information including stratigraphic nomenclature (Figure S1) for the study area, general flow geomorphology (Figure S2), major structures in the study area (Figure S3), reservoir pressure prediction (Figure S4), and Volume comparison of supercritical CO2 (Figure S5).
• Additional subsurface data including available petrophysical well logs (Table S1), stratigraphy interpretation (Table S2), and parameter description for storage resource estimation (Table S3).
hydrogeologic properties essential for any quantitative assessment of potential for CO2 storage.To address these data gaps, Pacific Northwest National Laboratory (PNNL), in partnership with the U.S. Department of Energy (DOE) Office of Fossil Energy & Carbon Management (FECM), has pioneered both laboratory 13, 20-25 and field pilot studies examining the potential for large-scale injection and storage of CO2 and natural gas 26 in flood basalts.Early experiments suggested rapid chemical reaction of CO2 in water saturated basalts to form stable carbonate minerals 20 .PNNL's analyses of data collected at WBPP confirmed these results at field conditions, successfully storing 977 tons of supercritical CO2 (scCO2) in several interflow zones of the Grande Ronde Basalt (GRB) on the site of the Wallula pulp and paper mill in eastern Washington State.Post-injection sidewall core samples and hydrologic simulation reported that up to 60% of injected CO2 had been incorporated into carbonate minerals within two years (2013-2015) of injection 27 .These previous studies have driven significant interest within the research, policy and investment communities to explore the potential of this approach as a safe, secure path to permanent geologic CO2 storage.With Congressional expansion of the U.S.'s 45Q tax credit in 2022 (the Inflation Reduction Act), the PNW has an unprecedented opportunity to leverage a groundswell of interest and enthusiasm from potential project developers including direct air capture (DAC) and point source capture companies.Based on the WBPP field tests, reservoir simulation, and geochemical analysis, this paper provides a robust CO2 storage resource estimation for anticlinal traps in CRBG basalt reservoirs.These new capacity estimates provide novel and timely context to our understanding of where and how commercial-scale basalt-hosted storage might deploy at favorable locations in the PNW.This work is also intended to fill critical knowledge gaps and provide support efforts by U.S. EPA and project proponents seeking to implement UIC Class VI permitting (76 FR 56982) for this class of lithologies (Figure 1).

161 Figure 1 .Figure 2 .
Figure 1.Conceptual illustration of deep (>800 m) stacked Columbia River Basalt Group reservoirs in the Pacific Northwest that can accommodate commercial-scale carbon capture and storage

287Figure 3 .
Figure 3. Well correlation between the three key wells used to characterize study area potential for commercial CO2 storage.Each flow member consists of interflow aquifers (blue intervals, C1-C14, K1-K16, and W1-W17) and massive flow interiors.See Figure 2 for well locations and major regional structural features.Histogram (left) shows the thermal neutron porosity distribution, average porosity, and standard deviation within the Grande Ronde Basalt (802 -1,252 m depth interval, 858 data samples) from Wallula Basalt Pilot #1 well; and (right) the thermal neutron porosity distribution, average porosity, and standard deviation within the Grande Ronde Basalt (812 -1,068 m depth interval, 714 data samples) from 100 Circles #1 well.Inset box shows average porosity (solid green line) and standard deviation (dotted red line).All depths are depth below ground level.

390 7 .Figure 4 .
Figure 4. Carbon dioxide density analysis based on the downhole condition in the Wallula well.a. plot of subsurface pressure versus temperature.The pressure and temperature limits (304.13K and 7.3773 MPa) above which CO2 is supercritical (light blue shaded area).b. temperature versus depth.A geothermal gradient line is shown for a temperature gradient of 19.36 K per 1 km.c. plot of pressure versus depth showing normal hydrostatic pressure gradient (9.79 MPa/km).d.CO2 density versus depth using pressure and temperature inputs from Figure 4b and Figure 4c.Critical depth (752 m below ground level) is the minimum depth for scCO2.e. enlarged view of supercritical section of Figure 4d showing the variation and average scCO2 density (644 kg/m 3 ).
554 investors and the local communities who could one day 555 host basalt-based projects here and around the world.556 While the commercial-scale CO2 storage potential of 557 sedimentary rocks has been proven by intensive 558 technology research, development, deployment and growing commercial adoption over the past 20 years, the PNW's CO2 sources-as well as more than 30% of global CO2 emissions 59 -are located far from highcapacity sedimentary storage resources, which risks leaving these facilities stranded without suitable storage options.In the PNW region and around the world, basalt formations represent one of the most attractive alternative geologic storage options due to their potential for rapid mineralization of CO2, widespread geographic distribution, and potentially large storage capacity 20, 60 .However, significant work remains to support selection and development of the storage complexes to serve commercial-scale demand from the existing and potential CO2 sources in this growing industrial area-including developing and validating best practices for sustained, large-scale injection; technologies for characterization and monitoring to identify and mitigate leakage and geomechanical risks; and of the full technoeconomic evaluation of region-specific, levelized per-ton storage costs.To address these research gaps crucial to de-risking and demonstrating a commercial-scale storage complex in this region, future projects will leverage expertise gained through the successful pilot-scale demonstration of CO2 storage and mineralization at the WBPP; and development of Iceland's Orca project (Carbfix). 7,61,62 F work, including our recently-funded stratigraphic wells, will build upon knowledge developed under these field projects through a focused effort to address barriers to commercial-scale mineralization storage in basalt reservoirs, and specifically at selected sites in the PNW and beyond.CO2 sequestration via mineralization provides viable solutions for the U.S. (e.g.Snake River Plain, Central Atlantic Magmatic Province, upper Midwest), Japan, India, Siberia, and southern Africa that lack thick, regionally continuous sedimentary basins suitable for conventional CO2 storage.
) based on anticlinal sandstone reservoirs to use 282 Furthermore, we used a simplified cylindrical model to 283 calculate the radius of the critical pressure front and delta 284 pressure resulting from one injection well.In the study 285 area, the initial pressure of the storage reservoir is 7.259 286 MPa at an elevation of -625.4 m (below mean sea level).