A potential for climate benign direct air CO2 capture with CO2-driven geothermal utilization and storage (DACCUS)

To reduce the overaccumulation of carbon dioxide (CO2) in the atmosphere, direct air CO2 capture (DACC) technologies must (a) satisfy the process requirements for heat and electricity with energy that has few if any CO2 emissions, and (b) physically isolate the CO2 from the atmosphere after its extraction from the air. To isolate the CO2 from the atmosphere at meaningful scale, the CO2 will likely need to be geologically stored in deep saline aquifers. Here we propose to leverage geologic CO2 storage (GCS) in sedimentary basin geothermal resources to produce geothermal heat and electricity for the process energy requirements of solid sorbent DACC. This sedimentary basin CO2-driven geothermal utilization (SB-CO2DGU, also known as CO2 Plume Geothermal) circulates some of the emplaced CO2 to extract geothermal heat in a closed loop between the subsurface reservoir and surface geothermal facility. The proposed integration of DACC and CO2-driven geothermal Utilization and Storage (DACCUS) adds CO2 from the air to this closed loop system that produces renewable energy for use in the DACC process. The strategy first primes the GCS reservoir with CO2 from large point sources, and then integrates CO2 from DACC facility to form the DACCUS system. We focus on the process integration of DACCUS and present a case study of its potential deployment and scaling in the Gulf Coast of the United States. We combine data from prior analyses for a novel investigation of two DACCUS configurations: (1) a DACCUS heat system uses the geothermal heat to regenerate the solid sorbent in the DACC process, and (2) a DACCUS heat and power system uses the electricity generated from the produced geothermal heat for the DACC process. In general, deeper CO2 storage reservoirs (>3.5 km) with higher geothermal temperature gradients (>35 °C km−1), may provide sufficient production wellhead temperatures (>100 °C), and satisfy the electric load in 93% of the combinations of reservoir characteristics we examined.


Introduction
Scientific consensus overwhelmingly concludes that societies need to slow, stop, and reverse the flow of greenhouse gases like carbon dioxide (CO 2 ) to the atmosphere in order to have a chance of averting the more serious environmental, and thus economic and social, consequences of climate change (IPCC 2022).Stabilizing global mean surface temperatures at 1.5 • C or 2 • C above pre-industrial levels requires 'negative emissions' approaches to begin removing CO 2 from the atmosphere around 2030, and for society to be completely net-negative later this century (Masson-Delmotte et al 2018, Minx et al 2018, Creutzig et al 2019).This transition must occur while still providing cost-effective energy to power economies and well-being (Fuss et al 2018, Minx et al 2018).
Natural approaches to negative emissions rely on ecological processes (e.g.photosynthetic conversion of CO 2 and water into plant tissue and its sequestration into soils), whereas technological approaches rely on engineered processes (UNEP 2020).Bioenergy CO 2 capture and storage (BECCS) and direct air CO 2 capture (DACC) are most investigated for their ability to extract large quantities of CO 2 over relevant timescales (Minx et al 2018, Creutzig et al 2019).BECCS relies on natural photosynthesis to remove CO 2 from free air and the CO 2 must then be separated during a conversion process.DACC uses liquid solvents or solid sorbents that react with air and selectively remove CO 2 .The CO 2 is separated by an extraction and regeneration.The commonly considered method to, in essence permanently, isolate the CO 2 from the atmosphere is geologic CO 2 storage (GCS) (Bielicki et al 2015, 2016b, Deng et al 2017), where the CO 2 is emplaced in deep (>800 m), porous, and permeable aquifers.If the sedimentary basin containing the aquifer has a sufficient geothermal heat flux (SedHeat 2013), the emplaced CO 2 may be used to extract geothermal heat by producing in situ brine that is already hot (Buscheck et al 2012(Buscheck et al , 2013(Buscheck et al , 2016)), or using the emplaced CO 2 as a heat extraction fluid.This latter method is sometimes referred to as CO 2 Plume Geothermal (Randolph and Saar 2011), where some of the geologically stored CO 2 is circulated between the aquifer and the surface through injection and production wells.The heat in the CO 2 that is produced to the surface can be used directly or converted to electricity, before the cooler CO 2 is reinjected into the aquifer.
Here we introduce a strategy to leverage GCS where the geothermal resource can be a source of process energy for DACC.This integration of DACC and SB-CO 2 DGU could be a climate-benign direct air CO 2 capture, utilization, and storage (DACCUS) system (figure 1).The strategy first geologically stores enough CO 2 from point sources to prime the geothermal heat extraction system, and then the DACC facility is added and the CO 2 extracted from the air becomes the only input of CO 2 .Depending on the reservoir characteristics (e.g.permeability, depth, geothermal temperature gradient), SB-CO 2 DGU could at least partially offset process energy requirements.
Common approaches to DACC use a chemical solid sorbent or a liquid solvent to extract CO 2 from air.These adsorbants must be heated to release the CO 2 and regenerated so that they can be reused.Here, we consider a DACC process with a chemical solid sorbent because the required regeneration temperature (80 • C-120 • C) is compatible with the low-grade heat resource in sedimentary basins (Buscheck et al 2016) and is much lower than is required for a liquid solvent (∼900 • C) (Wurzbacher et al 2016, Beuttler et al 2019, Climeworks 2021, McQueen et al 2021, Thermostat 2021).In addition to heat, the process also requires electricity to blow air through the sorbent, open and close valves, move fluids in the systems, and for CO 2 compression (IEA 2022).
We investigate two options for climate-benign DACCUS, where the produced geothermal heat is (1) used to regenerate the solid sorbent, or (2) converted to electricity in a direct CO 2 geothermal power plant for use in the DACC process and the excess sensible heat is used to regenerate the sorbent.We place the deployment of these systems in the context of onshore sedimentary basin geothermal resources in the U.S. Gulf Coast region and projections of the evolution of coal and natural gas electricity generating infrastructure that could provide the CO 2 to prime the SB-CO 2 DGU reservoirs.

DACCUS
Figure 1 shows the two climate-benign DACCUS configurations we consider: 1.Heat system: SB-CO 2 DGU provides the heat to regenerate the solid sorbent, and thus the enthalpy of the heat source into the DACC system (h HS,in ) is the enthalpy of the CO 2 at the production wellhead.2. Heat and power system: The heat extracted by SB-CO 2 DGU is used to generate electricity, and the excess sensible heat is used to regenerate the solid sorbent.In this configuration h HS,in is the enthalpy of the circulated CO 2 after the turbine in the direct-CO 2 geothermal power plant.
The heat provided by the SB-CO 2 DGU system is where ṁHS is the mass flow rate of the heat source (i.e.CO 2 circulating through the SB-CO 2 DGU system) and h HS,out is the enthalpy of the heat source out of the DACC system.Prior work (Adams et al 2015) maximized net power for a direct CO 2 power plant over a range of reservoir parameters and system designs (table 1) by integrating process-based electricity generation with thermodynamic models for flow through wells (Adams et al 2014(Adams et al , 2015) ) that incorporated prior work on thermo-fluid dynamic sedimentary basin geothermal reservoir simulations (Randolph and Saar 2011).The present work builds on those prior analyses and thus the results depend on the approaches and assumptions embedded in them.For example, a mesh with an infinite number of nodes to represent a sedimentary basin geothermal reservoir may yield a reservoir impedance as much as 50% higher than that of a course (Ravilov 2020).As a result, the representation and simulation of the sedimentary basin geothermal reservoir in early work (Randolph and Saar 2011) influences the mass flow rate ( ṁHS ) and the corresponding temperature and pressure of the CO 2 at the production wellhead and after the turbine that we use from (Adams et al 2015).Since we rely on results from that sequence of prior work, other assumptions   The annual capacity of a DACC facility to extract CO 2 from the air (C DACC ) is where η q is the heat exchange efficiency between the heat source and the DACC facility, θ reg is the specific thermal load to regenerate the solid sorbent and liberate extracted CO 2 , and t h is the operating hours per year: t h = CF•8760 where CF is the capacity factor of the DACC facility.The electrical load of the DACC is estimated by where λ DACC is the specific electric load for the DACC facility.
We use as a base case values from prior work (McQueen et al 2020): θ reg = 1600 kWh th /tCO 2 , λ DACC = 500 kWh e /tCO 2 , CF = 90%, η q = 85%, and a 70 • C outlet temperature of the CO 2 from the DACC device (T HS,out ).This outlet temperature is used with the appropriate pressure in REFPROP (Lemmon et al 2018) to estimate h HS,out .

Potential deployment in the U.S. gulf coast
We consider hypothetical but realistic scenarios for deployment of climate-benign DACCUS in the U.S. Gulf Coast region.This region has many substantial point sources of CO 2 that are widely distributed and likely to persist for decades (Middleton et al 2015), well-characterized GCS reservoirs with large CO 2 capacities (Blondes et al 2013), and suitable geothermal heat fluxes and aquifer temperatures (SMU 2022).
Each year, the U.S. Department of Energy provides comprehensive projections of the U.S. energy system, including regional projections of electricity generating capacity, which include likely additions and retirements of capacity.This Annual energy outlook (AEO) provides results from the implementation of various cases (e.g.Reference, High Oil Price, Low Oil & Gas Supply) in the National Energy Modeling System (EIA 2022a).For sourcing CO 2 for SB-CO 2 DGU, we use Reference Case projections to the year 2050 (EIA 2021) of CO 2 production from coal (CO coal 2 ) and natural gas (CO natural gas 2 ) electricitygenerating capacity in the East South Central, West South Central, and South AtlanticFor the subsurface emplacement of this CO 2 with GCS, we consider 25 of the 27 storage assessment units (SAU) in the U.S. Gulf Coast region (United States Geological Survey 2013) due to data availability.We use the locations and extents of the aquifers as potential GCS reservoirs as well as their reservoir depths (D), net porous thicknesses (b), porosities (φ ) and the densities of CO 2 in the reservoirs (ρ CO2 ).Reservoir pressures are estimated by multiplying the normal hydrostatic pressure gradient (10.53 kPa m −1 ) by D and adding atmospheric pressure.The temperature of each reservoir is estimated by the REFPROP library (Lemmon et al 2018), using ρ CO2 and the reservoir pressure as inputs.
We assume that GCS begins in the year 2025, at a pace where a SB-CO 2 DGU reservoir is primed with enough CO 2 for a climate-benign DACCUS system to begin operation after a five year priming (T prime ).
The number of potential DACCUS systems that can be deployed in a candidate reservoir depends in part on the amount of CO 2 that is needed to prime the reservoir, M CO2,prime (Mt), where V CO2,prime is the volume of CO 2 required to prime the reservoir: where N CP is the number of coupled inverted fivespot injection/production well patterns (in prior work, N CP has been referred to as the 'Configuration Number' (Bielicki et al 2016a)-each of which contains an injection well in the center of a square with side length L with a production well at each of the four corners-and ε is the efficiency by which the emplaced CO 2 occupies the pore space between the injection and production wells (0.36). 3he CO 2 injection rate per well is: where T prime is the five-year priming time, and N inj,well is the number of injection wells and is equal in number to N 2 CP .The upper bound of ṁinj,well is limited to 1 Mt yr −1 , which is an accepted upper limit for industrial CO 2 injection wells (Middleton et al 2020).The number of SB-CO 2 DGU systems can be deployed for climate-benign DACCUS in each of the 25 candidate aquifers in the region is thus:

Sensitivity and uncertainty analyses
Given the ranges of relevant parameter values for the DACCUS system and the potential GCS reservoirs, we conduct sensitivity and uncertainty analyses for the effects of key uncertain input parameters on the performance and deployment of DACCUS systems.

DACCUS performance
We consider the effects on the electricity load and capacity of DACC systems (L DACC and C DACC , respectively) by varying θ DACC,reg (1200-2000 kWh th /tCO 2 ), λ DACC (150-500 kWh e /tCO 2 ), and T HS,out (30 • C-70 • C), which are from relevant literature (Adams et al 2015, Fasihi et al 2019).The range of values are discretized with a step equal to ten and iterated two times.

DACCUS deployment
The USGS data for the potential GCS reservoirs include minimum, most likely, and maximum estimates, which result from the shape parameters (α 1 , α 2 ) of the Beta-PERT distribution: where µ Beta-PERT is the mean and is defined as: To conduct a Monte Carlo analysis, the continuous distributions in equations ( 8) and ( 9) were reconstructed for each variable using their minimum, most likely, and maximum values.These distributions were randomly sampled 10 000 times to determine the amount of CO 2 needed to prime the reservoir, the geothermal gradient, the DACC capacity, and the number of system to be deployed.

DACC plant capacity
The maximum production wellhead temperature for a 5000 m deep reservoir with a 50 The maximum production wellhead temperature is a viable heat source when above 100 • C, which only occurs when the geothermal temperature gradient is 50 • C km −1 in the shallower reservoirs we consider (2500 m and 3500 m): 100.4 • C and 132 • C, respectively.
With a SB-CO 2 DGU Heat System, the results in figure 2 show four 'scythes' for the dependence of DACC capacity and electric load on the production wellhead temperature.Each scythe results from the combination of reservoir depth and geothermal temperature gradient that yields the same reservoir temperature and maximum production wellhead temperature.There are more vertically-oriented results for N CP = 7, and many trajectories bend toward lower heat source temperatures with higher DACC capacities and electric loads.These results are due to the economies of scale with larger well patterns; designs where N CP is large have more combinations where the production wellhead temperature is greater than 100 • C. The scythe for the 2500 m depth is constrained due to the 80 • C-100 • C regeneration temperature requirement of the solid sorbent DACC system.
Figure 2 shows the effects of the production wellhead temperatures and reservoir permeabilities, where departures from linear relationships are evident at the higher mass flow rates.
All else constant, higher permeability reservoirs facilitate higher mass flow rates and reservoir heat extraction for a given pressure drop.But these effects are partially offset by the effect of higher production wellhead temperatures.Hotter CO 2 is less dense and, for a given pressure drop, the mass flow rate will decrease because it is proportional to the square of the density of the fluid.For higher permeabilities, the mass flow rate is limited to 30 kg s −1 , to be consistent with the 1 MtCO 2 yr −1 operational maximum.
Higher geothermal temperature gradients enable higher capacity DACC systems (and corresponding electric loads).Two of the five combinations of geothermal temperature gradient and reservoir depth that are viable for the SB-CO 2 DGU heat system yield a viable heat source for the SB-CO 2 DGU heat and power system (figure 3): 50 • C km −1 geothermal temperature gradients in 3500 m or 5000 m deep reservoirs.This reduction in the combinations of reservoir parameters that are viable for DACCUS when the geothermal heat is first used to generate electricity is due to lower temperatures at the outlet of the turbine.The CO 2 expands through the turbine, and as a consequence it experiences an enthalpy drop that results in lower temperatures and pressures.
The electric loads are 0.28-0.91MWe for the smaller DACC systems (N CP = 1) and 9.0-43 MWe for the larger systems (N CP = 7).These electric loads can be provided by SB-CO 2 DGU heat and power systems in 95.5% and 93.3% of the systems with viable heat sources.We quantify this ability for the SB-CO 2 DGU system to provide the electricity for the DACC system by subtracting the estimated DACC electricity load from the estimated SB-CO 2 DGU electricity generation to yield the 'SB-CO 2 DGU electricity generation in excess of DACC electric load' in figure 3. Higher heat source temperatures enable more DACC capacity, but the corresponding increase in electric load decreases the excess SB-CO 2 DGU electricity generation.
The results of the sensitivity analyses suggest that the maximum DACC capacity for the SB-CO 2 DGU Heat system is higher with (i) lower specific thermal loads or (ii) higher heat source outlet temperatures, relative to the results from the base case parameter values in section 2.1 (see figure S1 in the supplemental information, SI).With the SB-CO 2 DGU Heat and power system, (iii) lower specific electrical loads, or (iv) higher specific thermal loads result in higher SB-CO 2 DGU electricity generation relative to the DACC load-such that the generation in excess of the load is higher-relative to the results from the base case values (see figure S2 in the supplemental information, SI).The relationships in (i) and (ii) are evident in equation (2); for (iii), equation (3) shows that the electric load decreases with specific electrical load, which all else equal would result in an increase in excess electricity generation from the DACCUS system.The positive relationship in (iv) is less direct, but arises because of the combination of equations ( 2) and (3): lower specific thermal loads result in higher DACC capacities, which in turn result in higher DACC electric loads.These relationships highlight an important tradeoff between the specific electrical load and the specific thermal load which would be considered when optimizing the DACCUS system.In general, higher specific electrical loads (θ reg > 350 kWh/tCO 2 ) and lower specific thermal loads (λ DACC < 1800 kWh/tCO 2 ) result in a deficit of electricity generation relative to load and thus the DACCUS system would require electricity from another source or the electricity grid.For the smaller DACCUS system, the excess electricity generation decreases from 1.1-1.4MWe (1.2 MWe with base case values) in the deep (5000 m) reservoirs with lower permeability (10 −15 -10 −13 m 2 ) to -0.4-0.4MWe (-0.07 MWe with base case values) in the other viable reservoirs.For the larger DACCUS system (N CP = 7), the excess generation decreases from a maximum of 50-66 MWe (55 MWe with base case values) in most permeable and deepest reservoir (10 −11 m 2 , 5000 m) to a minimum of -17-12 MWe (-2.4 MWe with base case values) in the least permeable (5 × 10 −15 , 10 −14 m 2 ) reservoirs and 5000 m or 3500 m deep.
The SB-CO 2 DGU electricity generation is more likely to be greater than the DACC electric load with (a) lower turbine outlet temperatures, because of the increase in electricity generation and the decrease of DACC capacity, and (b) higher reservoir permeabilities, because of the increase in electricity generation due to higher mass flow rate allowed for the working fluid.

Case study of DACCUS deployment in U.S. Gulf Coast
We provide the results for the Norphlet Formation as an example of how the CO 2 from the three AEO regions can be used for SB-CO 2 DGU and DACCUS (figure 4, table 2).The amount of CO 2 that is geologically stored depends on the amount of CO 2 emissions in the source region and the injection mass flow rate limit (1 MtCO 2 /year/well).While the number of systems that are deployed using CO 2 from the ESC region is higher than for using CO 2 from the WSC region, there is less CO 2 from the ESC region that is geologically stored.The correlations between depth, net porous thickness, and porosity affect the uncertainty in the number of SB-CO 2 DGU systems deployed.The highest cumulative number of SB-CO 2 DGU systems deployed by 2050 in each SAU in the U.S. Gulf Coast for N CP = 7 are shown in figure 5.For eight formations, it is not possible to deploy the SB-CO 2 DGU systems with a priming time of five years because the CO 2 need is high due to their thickness.But other strategies can be investigated for those formations, such as having a two-phase deployment: GCS for longer than five years until the reservoir is primed and then SB-CO 2 DGU.
The results in figure 5(a) suggest that DACCUS cannot be deployed in formations with thicknesses greater than ∼100 m, because the CO 2 need of these reservoirs is quite large, but the injection mass flow rate is limited to 1 MtCO 2 /year/well.As a result, these reservoirs require more than five years to be primed.While DACCUS may not be suitable for these reservoirs, it may still be possible to use them for DACC with GCS.The results in figure 5(b) show the DACC capacity of a DACCUS Heat system for each of the 17 SAUs.The amount of CO 2 that can be extracted from the atmosphere ranges from 0.06 MtCO 2 yr −1 (Washita and Fredericksburg Groups, Rusk Formation, and James Limestone Deep) to 0.6 MtCO 2 yr −1 (Tuscaloosa and Woodbine Formations).

Discussion
This work provides a point of departure for the potential to use CO 2 that would be emitted to, or has been extracted from, the atmosphere to extract other CO 2 from the atmosphere.We demonstrate a possibility that geologically stored CO 2 could be used to produce geothermal heat and electricity for the process energy requirements for DACC, in part using the CO 2 from DACC.
Integrated systems analysis, such as in the present work, can be challenging in part because the models that are coupled may be developed elsewhere and need to be able to provide results for a full range of the input parameters rather than just that which is optimal for the (sub)system they address (e.g.Adams et al 2021).The coupled systems must be optimized for the performance of their integration, which is likely to yield operating parameters for the individual systems that differ from those that optimize the only individual systems (Bielicki 2009).
The DACCUS system here stacks results from prior work on SB-CO 2 DGU and DACC (Randolph and Saar 2011, Adams et al 2014, 2015, 2020b, Fasihi et al 2019, McQueen et al 2020, McQueen et al 2020), and thus incorporates the assumptions and approaches embedded in those analyses.A principal influence on the results here is the representation of the sedimentary basin geothermal reservoir, and specifically the reliance on prior results from reservoir simulations that modeled a flat reservoir of constant thickness, depth, porosity, and permeability.Increasing the discretization of the mesh that represents that homogeneous reservoir would asymptote to a higher reservoir impedance (Ravilov 2020), which may be quite higher.In fact, analytic solutions (Adams et al 2021, Birdsell et al 2024) may in principle represent an infinite mesh and provide the most robust results for the performance of a homogeneous reservoir.As a result, mass flow and geothermal heat extraction rates would likely be lower and thus the feasible regions of DACCUS would be confined to hotter, deeper, and more permeable reservoirs than the results here suggest.Yet actual sedimentary basin geothermal reservoirs are not homogeneous; their heterogeneity in depth, thickness, dip, structure, porosity, and permeability need to be considered (Eaton 2006) in order to understand the real potential of DACCUS and should thus be the end goal of investigations that seek to understand the performance of subsurface reservoirs.Heterogeneity may have effects that vary with its various manifestations.For example, mass flows and geothermal heat extraction may be larger in thief zones of higher porosity and permeability, whereas a reservoir thickness that varies within the reservoir may reduce mass flows and geothermal heat extraction.The net effect of heterogeneities on all dimensions is at present uncertain, with net effects likely being site-specific.
Future research could optimize the integrated DACCUS system as well as seek to understand how to leverage reservoir heterogeneity and strategically place wells for CO 2 flow that maximizes geothermal heat extraction while minimizing CO 2 needs (Bielicki et al 2023).
Scaling-up atmospheric CO 2 removal options, such as DACC, is a priority along with efforts to reduce CO 2 emissions before they enter the atmosphere (Smith et al 2023).Unlike other options for large-scale CO 2 utilization, namely for enhanced oil recovery, DACCUS avoids the potential for more, albeit perhaps delayed, CO 2 emissions, while it produces heat and power that can provide revenue.
The integration of DACC with SB-CO 2 DGU could provide useful savings to offset the expensive estimates of $500-600/t CO 2 for commercial DACC entities.For example, using a 1 km × 1 km SB-CO 2 DGU heat and power system to avoid electricity priced at $70 MWh −1 could save $0.15 M yr −1 -$0.48 M yr −1 .Savings such as these could complement financial incentives in the patchwork of policies and CO 2 prices to address CO 2 emissions.For example, the U.S. 45Q Federal tax credit could provide up to $180/tCO 2 for DACC with SB-CO 2 DGU, which equates to $0.41-$5.9M yr −1 for a SB-CO 2 DGU heat system and $0.88-$2.9M yr −1 for a SB-CO 2 DGU heat and power system over twelve years.In these results, up to 2% of the CO 2 mass flow rate could be provided by the DACC process, which could compensate for CO 2 migration elsewhere in the GCS aquifer.The balance of the CO 2 for the SB-CO 2 DGU system would be provided elsewhere and could receive $60/tCO 2 .Only a portion of the emplaced CO 2 is circulated to extract geothermal heat, so much of it could yield $85/tCO 2including the CO 2 that would be necessary to prime the reservoir.
For DACC to contribute the most to its potential to be a net-negative CO 2 energy technology, the process energy should have few if any CO 2 emissions associated with it.This goal can constrain DACC siting.For example, in the United States most of the geothermal power plants are in California and Nevada, and most nuclear power plants are located east of the Mississippi River (EIA 2022b).DACCUS may relieve siting constraints such as these and expand the locations where DACC plants may be sited.Although, if there is a deficit of electricity generation relative to load-which our results suggest is more likley with a combination of higher specific electrical loads (θ reg > 350 kWh/tCO 2 ) and lower specific thermal loads (λ DACC < 1800 kWh/tCO 2 )then the DACCUS system would require electricity from elsewhere and the net CO 2 reductions would need to consider the emissions from those sources.

Conclusion
We establish a potential for climate-benign DACCUS-Direct Air CO 2 Capture, Utilization, and Storage-where sedimentary basin CO 2 -driven geothermal utilization provides heat and power for the DACC process.In this work, deeper GCS reservoirs (>3.5 km) with higher geothermal temperature gradients (>35 • C km −1 ) may provide usable and sufficient production wellhead temperatures for produced geothermally-heated CO 2 to provide the process energy for DACC.The corresponding capacities (and electric loads) of DACC systems increase with depth and gradient.SB-CO 2 DGU can satisfy the electric load of the DACC facility in over 90% of the relevant reservoir characteristics we examined.Such an integration of CO 2 utilization for renewable energy production with DACC could improve efficiency, reduce costs, and increase the net reductions in atmospheric CO 2 and the broader system that provides the inputs DACC requires.
Approximately 2 GtCO 2 yr −1 is removed from the air by conventional land management, yet only 0.002 GtCO 2 yr −1 is removed by novel methods such as DACC (Smith et al 2023).To achieve goals for averting some of the most consequential impacts of climate change, such as those embodied in the 2015 Paris Agreement, the world must quickly and efficiently slow, stop, and reverse the flow of greenhouse gasses like CO 2 to the atmosphere.There are many independent options available, such as geothermal energy, GCS and DACC, and their combination in DACCUS may help accelerate the overhaul of energy systems worldwide.

Figure 1 .
Figure 1.Two potential system configurations for DACCUS: heat system and heat and power system.
characteristics and can range from 35 • C to 211 • C (Adams et al 2014, 2015).Since the sorbent regeneration requires heat or steam at or below ambient pressure (Fasihi et al 2019, McQueen et al 2020, Adams et al 2020a, Lebling et al 2022), we only consider heat sources at the production wellhead above 100 • C.

Figure 2 .
Figure2.DACC capacity and electricity load for climate-benign DACCUS heat system.The heat source temperature for this system is the production wellhead temperature, which, along with the mass flowrates, are fromAdams et al (2015).

Figure 3 .
Figure3.DACC electric load, SB-CO2DGU electricity generation, and SB-CO2DGU electricity generation in excess of DACC electric load for climate-benign DACCUS heat and power system.The heat source temperature for this system is the outlet temperature of the turbine.

Figure 4 .
Figure 4. Norphlet formation cumulative CO2 geologically stored, and cumulative SB-CO2DGU systems deployed between 2025 and 2050 (dots).Shaded areas represent the standard deviation of the cumulative CO2 geologically stored, while the bars represent the standard deviation of the SB-CO2DGU systems deployed.

Table 1 .
Characteristics of the SB-CO2DGU Reservoir and system design.
et al 2018) to estimate h HS,in .The production wellhead temperature of the CO 2 depends on the reservoir

Table 2 .
Summary of potential DACCUS deployment by 2050 in the norphlet formation.Correlations between depth, net porous thickness, and porosity influence the uncertainty in how many SB-CO2DGU systems can be deployed.The values shown are mean (standard deviation).