A new GIS-based analysis suggests Earth’s capacity to store CO2 in underground pore space may be far smaller than long-assumed, falling to roughly 1,460 gigatonnes once environmental, land-use, and drilling constraints are factored in. The finding raises concerns that future generations could face storage shortages unless emissions fall faster or alternative mineralization-based storage options mature. Full article >>
A U.S. Department of Energy–funded study has concluded that waste heat from the Farley nuclear power plant in Alabama could power a pilot-scale direct air capture facility, achieving an estimated 92.5% net carbon-removal efficiency. While technically feasible, such a project would face major economic hurdles, with analysts noting that high costs, low capture volumes, and dependence on incentives such as 45Q would make financing difficult. Full article >>
EnEarth plans to make direct air capture a component of Greece’s first industrial-scale carbon-capture and storage project, sending CO2 from both industrial emitters and a new DAC plant to the depleted Prinos oil field for permanent geological storage. Backed by €150 million in government support and aiming for operations as early as 2025–26, the project would create a major Mediterranean CO2-storage hub and deploy RepAir’s electrochemical DAC technology at scale. Full article >>
Equipment failures at major CCS projects in Norway and the United States—one leading to years of over-reported CO2 injection at Equinor’s Sleipner site and another causing a leak into an unintended formation at ADM’s Decatur facility—are raising fresh concerns about the reliability of underground carbon storage. The incidents highlight the need for stricter monitoring, transparent reporting, and stronger regulatory oversight as CO2 storage expands to support net-zero goals. Full article >>
CarbonCapture Inc. has shelved its ambitious Wyoming DAC project after competition from data centers and other industries made it nearly impossible to secure the clean power needed for large-scale air-capture operations. The company is now pivoting to Louisiana, where it has won a federal contract to study a 200,000-ton DAC-with-storage project that could anchor a new Gulf Coast carbon-removal hub. Full article >>
Occidental Petroleum is building STRATOS, a $1.3 billion direct air capture plant in West Texas that is slated to become the world’s largest facility of its kind, designed to remove up to 500,000 metric tons of CO2 per year and store it underground in the Permian Basin. Backed by partners including BlackRock and buyers such as Microsoft and Airbus, the project underscores both the surging corporate demand for high-quality carbon-removal credits and the growing debate over whether DAC can scale quickly enough to meaningfully cut emissions. Full article >>
Basics of DACPS
DACPS (dăk-p-s) involves using an industrial plant to capture CO2 gas from atmospheric air and then compressing it to a (semi-liquid) state.
The supercritical CO2 is stored long-term by injecting it deep (more than about 800 meters) underground into tiny pore spaces in a layer of sandstone or other sedimentary rock.
How CO2 is trapped in sandstone — at the microscopic scale
CO2 is trapped between rock (sand) grains as the CO2 flows through the rock (sandstone) and globules of CO2 become detached, halting further flow.
Below a depth of 800 meters, the temperature and pressure is greater than CO2's critical temperature and pressure of 31oC (87.8oF) and 73.8 bar (1071 psi), thus keeping CO2 in the supercritical (semi-liquid) state and does not revert back to gas.
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DACPS has six basic steps:
Extract CO2 gas from the atmosphere in a plant where fans blow air through an air contactor and CO2 molecules attach to either a liquid solvent or a solid sorbent (the two main types of DAC plants).
Release the CO2 from the solvent or sorbent using heat and/or water. The solvent/sorbent is reused.
Liquify extracted CO2 by compressing and cooling.
Transport the liquified CO2 via pipeline to underground injection wells.
Inject the CO2 deep into the ground into a sandstone or other permeable reservoir which is overlain by an impermeable layer such as shale (the caprock or topseal). Semi-liquid CO2 underground — being more buoyant (less dense) than surrounding groundwater and rock — tends to float upward toward the land surface through any openings in the overlying rock layers.
Trapped under the caprock, the CO2 flows laterally, outward from the injection well, fingering through the sandstone reservoir layer until there are only disconnected globules of CO2 in the sandstone pores and further advancement at the leading edge of the CO2 plume ceases.
Relationship of DACPS to DACCM and DACCS
DACPS and direct air capture with carbon mineralization storage () differ only in the mechanism that stores the CO2 in rock. DACPS stores the CO2 by physical trapping of the semi-liquid CO2 in the pore spaces of rock (typically sedimentary rock such as sandstone or limestone). DACCM stores CO2 by a chemical reaction in which semi-liquid CO2 reacts with basalt (or similar igneous rock) to form solid rock (limestone). . .
DACCS (direct air capture with carbon sequestration) is the traditional, widely used — general — expression that refers to underground storage of DAC-captured CO2, without regard to the mechanism that traps the injected CO2 underground. So, DACCS refers to both DACPS and DACCM.
Distinguishing between DACPS and DACCM — rather than lumping them together as DACCS — helps in understanding the geographic distribution of DAC projects, evaluating CO2 leakage potential and storage durability, and development of public policy.
The role and criticism of DACPS in CDR
DACPS is viewed by as a tool that is necessary for the world to reach during the transition from fossil fuels to energy sources that have low or zero greenhouse gas emissions. DACPS is widely criticized, however, for the potential to prolong the use of fossil fuels and the potential for hindering the scale-up of low-emissions energy sources such as solar.
Deployment status
Globally, there are DAC plants in operation that capture CO2 for use in products (direct air capture and use, DACU). And there are large-scale DAC plants that store CO2 underground using carbon mineralization (DACCM). But there is not yet a large-scale DAC plant in operation that stores CO2 in underground pore space (DACPS). This may change in 2025, however, when the oil company, Oxy, is expected to start up its new DACPS plant in west Texas (USA). The plant, named STRATOS, is designed to capture 500,000 tons of CO2 per year. . .
Injecting CO2 underground is nothing new for the oil industry as it has injected CO2 into underground pore space since the 1940s in (EOR) projects. Most CO2 used in EOR has come from naturally occurring CO2 gas deposits. Since 1972, increasingly more CO2 for EOR is coming from gas captured from the exhaust flues of industrial plants such as natural gas processing plants and ammonia fertilizer plants. DAC could supply EOR if economics are favorable.
In addition to STRATOS, nine other large-scale DACPS projects worldwide are in the planning stage (view table). Many DACCS projects that may use pore space storage (see CDR.fyi, search on DACCS) have pre-sold carbon credits for future delivery to buyers who are trying to meet their companies' net zero goals by the year 2050 — a deadline consistent with many national net-zero goals. Investors and government incentives in the form of grants or tax credits help drive many of projects.
Environmental impacts
Injecting CO2 underground can cause if injected with a high enough pressure to fracture rock underground. Semi-liquid CO2 stored underground can leak to the land surface through an injection well or an old oil or gas well in the storage area if CO2 degrades the steel well casing. CO2 can also to the land surface if a flow pathway through a topseal layer of rock is dissolved by carbonic acid that is created when CO2 dissolves in groundwater.
Carbon negative status
DACPS requires a significant amount of energy to capture and compress CO2. The amount of used in DACPS to capture and compress one ton of CO2 is currently estimated to be 2.17 , dropping to 1.44 MWh/tCO2 by year 2050.
For a 1-million-ton per year DAC plant, the 1.44 MWh/tCO2 equates to the annual energy use of 96,000 homes (assuming each home uses an average of 3.0MWh of energy annually). The energy would need to come from a low- or zero-carbon source for a DACPS project to be carbon negative (i.e., remove more carbon dioxide than the project produces). A cradle-to-grave assessment of a project is necessary for verifying the project will be carbon negative.
Cost per ton of CO2 captured
DACPS costs include the costs of: CO2 capture, compression, transport, underground storage, and monitoring. The total cost of removing and storing one ton of CO2 using DACCS (i.e., DACPS or DACCM) in 2020 was to be between approximately €175 to €400 per ton of CO2 removed. The estimate projected the cost to drop to roughly the €100 to €250 range by the year 2050 due to gains from technology advances and improved economy of scale.
Monitoring, reporting, and verification (MRV
The number of tons of CO2 removed from the atmosphere and stored in a DACPS project can be
using a flow meter at the injection wellhead.
Monitoring is aimed at detecting leaks of CO2 from the underground reservoir. Monitoring methods include monitoring wells, seismic mapping of the underground CO2 plume, and CO2 gas detectors installed in soil or on the land surface. Government regulations typically require an approved monitoring plan prior to approving a permit for a CO2 injection well.
Globally, at least MRV
have been developed for DACPS.
CO2 storage durability
CO2 stored in a geological formation (including DACPS projects) is to be virtually permanent (at least 10,000 years).
Long-term global CDR potential
DACPS, as well as the
geologic methods of CDR, are considered to be "novel" (new unproven) methods of CDR — compared to conventional, proven CDR methods (e.g., biochar, bioenergy with carbon capture and storage, afforestation).
A scenario has been for the year 2050 in which the novel methods annually supply about 2 of the total annual 10 gtCO2 of CDR that will be needed then in order to limit global warming to 2oC above pre-industrial (circa year 1850) levels. To visualize the potential scale of DACPS development in 2050, if DACPS supplies one-fourth (0.5 gtCO2 per year) of the annual 2 gtCO2, then 500 DACPS plants — each with 1 million gtCO2 annual removal capacity — will be needed.
