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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Reductant‐ or Light‐Driven ATP‐Independent Reduction of CO 2 by Nitrogenase MoFe Protein

Nitrogenase is a versatile metalloenzyme that activates and reduces small molecules like N 2 , CO, and CO 2 into value-added chemicals at ambient conditions. Previously, it is shown that the Mo-nitrogenase could reduce CO 2 to CO, but not to hydrocarbons, in an ATP-dependent reaction. Here, it is reported that the ability of the catalytic component of Mo-nitrogenase (MoFe protein) enables ATP-independent reduction of CO 2 to up to C 4 hydrocarbons in room-temperature reactions driven by a chemical reductant (Eu II –DTPA) or visible light (via CdS@ZnS (CZS) quantum dots). Moreover, an opposite deuterium isotope effect is observed on the Eu II –DTPA driven reactions of CO 2 reduction by MoFe protein and its V-counterpart (VFe protein), in that the former displays higher activities in H 2 O, and the latter displays higher activities in D 2 O. Furthermore, these results provide an important foundation for further mechanistic exploration of the nitrogenase-enabled, atypical Fischer–Tropsch type reaction that uses CO 2 instead of CO as a substrate; moreover, they serves as a potential template for the future development of nitrogenase-based applications that effectively recycle the greenhouse gas CO 2 into valuable fuel products.

C-C coupling↗
DOE OSTI2020

Understanding Support Effects of ZnO-Promoted Co Catalysts for Syngas Conversion to Alcohols Using Atomic Layer Deposition

Co 2 C, an emerging catalyst for the conversion of syngas to oxygenates, shows support-sensitive behavior that has not yet been fully explained. In this work, we characterize Co catalysts modified with ZnO atomic layer deposition on SiO 2 , carbon, CeO 2 , and Al 2 O 3 supports. We find that under syngas conditions, ZnO-promoted Co transforms into Co 2 C on SiO 2 , carbon, and CeO 2 , but not on Al 2 O 3 . Moreover, the support affects the extent of carburization: while the SiO 2 -supported catalyst carburizes completely, carbon- and CeO 2 -supported catalysts show incomplete conversion of Co to Co 2 C. These three catalysts also exhibit different oxygenate selectivities. In contrast, the modified Al 2 O 3 -supported catalyst retains the Fischer-Tropsch catalytic properties of metallic Co. By depositing increasing amounts of Al 2 O 3 by ALD on the SiO 2 support, decreasing Co 2 C formation and oxygenate selectivity occurs. In-situ XANES reveals that Al 2 O 3 prevents Co 2 C formation by enabling the ZnO to restructure into ZnAl 2 O 4 during reduction. Thus, in addition to modifying the active catalyst phase, the promoter can also strongly interact with the support, significantly impacting catalyst performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Nonadditive CO 2 Uptake of Type II Porous Liquids Based on Imine Cages

Type II porous liquids can potentially exploit the fluidity of liquids and sorption properties of porous sorbents, yet CO 2 uptake in porous liquids is still poorly understood. Molecular simulations and experiments are used to examine CO 2 uptake by a prototypical porous liquid composed of porous organic cages (CC13) in 2′-hydroxyacetophenone (2′-HAP). The simulations are in reasonable agreement with experimental measurements of CO 2 solubility and provide unambiguous information on the partitioning of CO 2 within microenvironments in the liquid. Analysis of CO 2 dynamics is performed using these simulations, including assessing the self-diffusivity of CO 2 in both the neat solvent and porous liquid. This offers insights into the kinetics of CO 2 uptake and transport in type II porous liquids based on imine cages. Experiments with type II porous liquids formed by dissolving CC13 in three different size-excluded solvents show nonadditive CO 2 absorption relative to predictions based on ideal volume additivity. This nonadditive absorption behavior is also observed in simulations. Nonadditive CO 2 uptake is also demonstrated in type II porous liquids based on another imine-based porous cage, CC19.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Harnessing the Hybridization of a Metal-Organic Framework and Superbase-Derived Ionic Liquid for High-Performance Direct Air Capture of CO 2

Direct air capture (DAC) of CO 2 has emerged as the most promising “negative carbon emission” technologies. Despite being state-of-the-art, sorbents deploying alkali hydroxides/amine solutions or amine-modified materials still suffer from unsolved high energy consumption and stability issues. Here, in this work, composite sorbents are crafted by hybridizing a robust metal-organic framework (Ni-MOF) with superbase-derived ionic liquid (SIL), possessing well maintained crystallinity and chemical structures. The low-pressure (0.4 mbar) volumetric CO 2 capture assessment and a fixed-bed breakthrough examination with 400 ppm CO 2 gas flow reveal high-performance DAC of CO 2 (CO 2 uptake capacity of up to 0.58 mmol g -1 at 298 K) and exceptional cycling stability. Operando spectroscopy analysis reveals the rapid (400 ppm) CO 2 capture kinetics and energy-efficient/fast CO 2 releasing behaviors. The theoretical calculation and small-angle X-ray scattering demonstrate that the confinement effect of the MOF cavity enhances the interaction strength of reactive sites in SIL with CO 2 , indicating great efficacy of the hybridization. The achievements in this study showcase the exceptional capabilities of SIL-derived sorbents in carbon capture from ambient air in terms of rapid carbon capture kinetics, facile CO 2 releasing, and good cycling performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Pd3Ag(111) as a Model System for Hydrogen Separation Membranes: Combined Effects of CO Adsorption and Surface Termination on the Activation of Molecular Hydrogen

Abstract The co-adsorption of hydrogen and carbon monoxide on Pd 3 Ag(111) alloy surfaces has been studied as a model system for Pd-Ag alloys in membrane and catalysis applications using periodic density functional theory calculations (PW91-GGA). We explored the effects of Pd–Ag surface composition, since segregation of silver towards and away from the surface has been suggested to explain the experimentally observed changes in H 2 activation, CO inhibition and reactivity. We found that CO pre-adsorbed on the surface weakens the adsorption of H on Pd 3 Ag(111) alloy surfaces irrespective of whether the surface termination corresponds to the bulk Pd 3 Ag composition, or is purely Pd-terminated. A higher coverage of H with CO present is obtained for the Pd-terminated surface; this surface also exhibits a larger range of chemical potentials for co-adsorbed hydrogen and CO. The barrier for H 2 activation increases with increasing CO coverage, but the surface composition has the largest impact on H 2 activation at intermediate CO coverage. The results imply that Pd-based membranes with typically ~ 23 wt% Ag are less prone to CO poisoning if the surface becomes Pd-terminated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Experimental study of three-dimensional CO 2 -water drainage and fracture-matrix interactions in fractured porous media

Estimation of CO 2 storage capacity in fractured porous reservoirs requires a better understanding of the CO 2 -water flow fundamentals in fracture-matrix systems. There are few core-flood experiments on three-dimensional CO 2 -water drainage in a fracture-matrix system, yet none have examined the impacts of the capillary continuity of fractures and fracture-matrix interactions. In this study, twelve drainage experiments were conducted in four fracture-matrix columns, each comprising a vertical stack of a cylindrical rock core, a filter paper serving as an analogue to a horizontal fracture, and a ceramic plate. Here, the core sample was surrounded by open space at the top and circumferential sides to model fractures, allowing for 3-D CO 2 -water drainage in the rock core and displaced water draining across the horizontal fracture. X-ray computed tomography was conducted to visualize the dynamic invasion/drainage processes in four rock core samples showing contrasts in anisotropy, permeability, and heterogeneity. Experimental results show (1) the equilibrium CO 2 saturations in the rock matrix vary from 0.10 to 0.60 at controlled capillary pressures up to 200 kPa, (2) the CO 2 saturations in the matrix increase with water saturation in the horizontal fracture resulting in better capillary continuity for water to drain across the fracture, and (3) the fracture water saturation can be enhanced by the non-uniform fracture capillary pressure and countercurrent flow of CO 2 and water across the fracture-matrix interface. In the case of high fracture water saturation, matrix CO 2 saturation largely depends on matrix anisotropy and heterogeneity. The core-scale experimental results contribute to understand the fracture-matrix interactions and CO 2 storage efficiency in fractured porous media.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Impact of salinity on morphology, growth, and pigment profiles of Scenedesmus obliquus HTB1 under ambient air and elevated CO 2 (10 %) conditions

Certain microalgal species, such as Scenedesmus obliquus strain HTB1, thrive under high CO 2 concentrations, making them promising for carbon sequestration to mitigate climate change. Isolated from the Baltimore Inner Harbor, HTB1 grows faster with 10 % CO 2 than with ambient air. To investigate its responses to salinity and elevated CO 2 , two experiments were conducted. In the first, HTB1 was cultured at seven different salinities (0, 17.5, 20, 22.5, 25, 27.5, and 30 ppt) (parts per thousand) under ambient air. Higher salinity caused cell shrinkage, color changes from green to pale white, reduced pigments like zeaxanthin, lutein, and chlorophyll b, but increased canthaxanthin. Growth declined significantly above 22.5 ppt. The second experiment compared HTB1's response to salinity (0, 10, 20 ppt) under air and 10 % CO 2 . Cultures under 10 % CO 2 showed minimal color changes, while those under air shifted from green to brown, with salinity having less inhibitory effects on growth under elevated CO 2 . Interestingly, lutein and canthaxanthin levels rose with salinity in 10 % CO 2 . These findings indicate that elevated CO 2 mitigates salt stress in HTB1, reducing its impact on growth and promoting adaptive pigment changes. This study sheds light on how salinity and CO 2 interact to influence HTB1's morphology, growth, and pigment composition, enhancing our understanding of its resilience and potential applications.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2020

From electricity to fuels: Descriptors for C 1 selectivity in electrochemical CO 2 reduction

Electrochemical reduction of carbon dioxide (CO 2 RR) over transition metals follows a complex reaction network. Here, we combine observations from experimental literature with a theoretical analysis of energetics to rationalize that not all intermediates in the reduction of CO 2 are formed through direct protonation steps. We derive a selectivity map for two-electron products (carbon monoxide (CO) and formate) on pure metal surfaces using only the CO and OH binding energies as descriptors. For the pure metals that are selective towards CO formation, the variation of the CO binding energy is sufficient to further subdivide the map into domains that predominantly form H 2 , CO, and more reduced products. Our analysis rationalizes experimentally observed product distributions in CO 2 RR across pure metal systems. Overall, we highlight the need for additional material screening descriptors for CO 2 R and the importance of considering competition from the elementary steps of the hydrogen evolution reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Developing new alkaline ceramics as possible CO 2 chemisorbents at high temperatures: The lithium and sodium yttriates (LiYO 2 and NaYO 2 ) cases

In this work, lithium and sodium yttriates (LiYO 2 and NaYO 2 ) were synthesized, characterized and tested as possible carbon dioxide (CO 2 ) captors. All the experimental syntheses and analyses were supported by the theoretical thermodynamic calculations, showing that both ceramics would be able to chemisorb CO 2 in a wide temperature range. Therefore, both ceramics were prepared by solid-state reaction and structurally characterized. In fact, the structural characterization evidenced that sodium atoms are located in a octahedral close-packed structure, while lithium ions are not so packed. The lithium ions are, indeed, in a highly distorted tetrahedron, tending to square-planar coordination. Then, based on the theoretical and structural analysis, LiYO 2 and NaYO 2 samples were investigated for the CO 2 capture process through dynamic and isothermal thermogravimetric experiments. All these experiments showed that LiYO 2 has better CO 2 capture properties than NaYO 2 , which was further correlated with the crystal structures of each ceramic. Furthermore, both ceramics presented similar CO 2 capture efficiencies regardless of the CO 2 concentration. Finally, LiYO 2 sample was tested for cyclic CO 2 chemisorption-desorption processes. The obtained results showed that the CO 2 capture efficiency is maintained high at least through 10 cycles. Therefore, these alkaline yttriates seem to present interesting alternatives as high and moderate temperature CO 2 captors, applicable for post-combustion industrial capture processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

High-current-density electrosynthesis of formate from captured CO 2 solution by MOF-derived bismuth nanosheets

Greenhouse gas emissions present a significant challenge to humanity, and utilizing renewable electricity to convert emitted CO 2 into value-added products offers a promising solution; however, traditional CO 2 capture and regeneration processes remain energy-intensive, restricting the overall system efficiency and decarbonization efficacy. In this study, an advanced direct reduction of captured CO 2 with large current densities for formate electrosynthesis was demonstrated without the need for CO 2 regeneration or compression. The bismuth nanosheet (DRM-BiNS) was synthesized by direct reduction of a Bi-based MOF, representing a new class of catalytic materials with a large surface area and interconnected pores, suitable for the direct reduction of captured CO 2 . By seamlessly combining experimentation and simulation, insights into the structure-parameter-performance relation were acquired in a flow cell setting, including critical membrane-electrode distance, cell orientation, and pumping flow rate. Important flow-cell components, such as catholyte volume, electrode substrate, membrane choice, and ionomer type, were also carefully examined to enhance the cell performance. In sharp contrast to prior studies limited to current densities below 20 mA/cm 2 in bicarbonate-based captured CO 2 solutions, this work demonstrates a remarkable current density of 300 mA/cm 2 with an FE to formate comparable to the case with gas-fed CO 2 reduction. Moreover, the process sustained an FE above 50% at a high current density of 500 mA/cm 2 . The DRM-BiNS catalyst exhibited outstanding selectivity, activity, and stability, significantly outperforming oxide-derived bismuth nanosheets (OD-BiNS) in captured CO 2 reduction. Furthermore, these findings offer critical insights into the development of sustainable and scalable CO 2 utilization technologies.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Effects of Co doping on the structure and physicochemical properties of hausmannite (Mn 3 O 4 ) and its transformation during aging

Hausmannite is a common low-valence manganese oxide mineral with a distorted spinel structure in surficial sediments. Although natural Mn oxides often contain various transition metal (TM) impurities, few studies have addressed the substitution mechanisms of TMs, such as cobalt (Co), with hausmannite and induced changes in the mineral physicochemical properties. In this study, Co-doped hausmannites with final Co/Mn molar ratios of 0.05 and 0.11 were synthesized and characterized by wet chemical analysis, powder X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR), high resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS). Co-doped samples have larger crystallite sizes and smaller specific surface areas than those of the hausmannite without Co. The Co cations exist in a mixed-valence of +3 and + 2. Powder XRD and acid dissolution experiments indicate that Co incorporates into the mineral structures, and increases the mineral structural stability. Co K-edge extended X-ray adsorption fine structure (EXAFS) analysis demonstrates that Co likely substitutes for lattice Mn(III). After aging at room temperature for three years, 14.1 ± 1.9% of pure hausmannite is transformed to manganite while only 2.6 ± 0.7% of manganite appears in the aged Co-doped sample with an initial Co/Mn molar ratio of 0.10. Finally, these results provide new insights into the incorporation mechanisms of TMs into low valence Mn oxides, and the stability of these minerals in natural environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Effect of CO 2 on the water slip flow at silica surfaces for nanometer slit pores of talc

In our previous study, Molecular Dynamics (MD) simulated water flow with no dissolved gas in nanometer slit pores of the hydrophobic talc surfaces revealed a slip length of about 0.5 nm, which is close to the size of “water exclusion zone” but much less than experimental slip length. Atomic Force Microscopy (AFM) imaging confirmed the presence of pancake shape nanobubbles at the hydrophobic talc (001) surface (size from tens to hundreds of nanometers). The effect of CO 2 on water slip flow in talc nanopores is reported to reveal the importance of dissolved gas for confined fluid flow. MD simulated 7 nm CO 2 nanobubbles were found to attach and spread at the talc (001) surface, consistent with the AFM observation. Simulated CO 2 saturated water flow in the slit pores of talc (001) surfaces predicted the generation of CO 2 nanobubbles at the end of the slit pore, due to the stabilization of a CO 2 film at the talc (001) surfaces and a water barrier at the edge surfaces of talc. A “critical thickness” of about 1.5 nm was found for CO 2 nanobubbles to be stabilized at the end of the talc (001) surface. With 1.5 nm CO 2 nanobubbles at the talc (001) surface of a 6 nm slit pore, a water slip length of 1.8 nm was determined. Furthermore, the nanometer slit pore simulations with dissolved CO 2 in water revealed an increased slip length. It is expected that an increased slip length value would be found with an increased CO 2 film thickness.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

The impact of capillary heterogeneity on CO 2 flow and trapping across scales

Capillary heterogeneity has been identified over the last decade as a key control on subsurface CO 2 flow behavior during geological CO 2 sequestration. These heterogeneities can be formed in all sedimentary rocks, ranging from slight variations in the sand grain sizes to extensive sequences of interbedded sands, shales, and limestones. Capillary heterogeneity has been largely, although not entirely, overlooked in subsurface flow modeling because it is assumed to only directly influence fluid redistribution over scales of centimeters to meters. However, even small-scale fluid movements can result in dramatic impacts on the mobility and trapping of the CO 2 over kilometers. Therefore, neglecting capillary heterogeneity at multiple scales could potentially lead to errors in modeling and predicting field-scale plume migration. In this review paper, we aim to provide a consistent overview to (1) establish that capillary heterogeneity can have a major impact on CO 2 plume migration, (2) establish the respective length scales at which capillary heterogeneity matters, and (3) provide guidance for numerical modeling. This review covers pertinent literature and extracts key observations from the core to the field scales. Experimental studies have shown that millimeter-decimeter scale capillary heterogeneity can cause the so-called capillary heterogeneity trapping in addition to pore-scale residual trapping. Even at such a small scale, capillary heterogeneity can already lead to complex upscaled constitutive relationships, such as flow-rate dependent and anisotropic relative permeability, which affects field-scale CO 2 migration even when field-scale heterogeneities are present. Under gravity-dominated flow regimes, centimeter-meter scale capillary heterogeneity can entrap a significant amount of CO 2 at field scale, not just after imbibition but also during drainage. In certain cases, the presence of capillary heterogeneity can even completely stop the vertical movement of the CO 2 plume, hence greatly reducing leakage risks. At meter-kilometer scale, the influence of capillary heterogeneity is more pronounced and can hinder or redirect CO 2 migration in both lateral and vertical directions. The impact of capillary heterogeneity across multiple spatial scales poses a great challenge in modeling CO 2 migration at field scale, because it is practically impossible to build a field-scale earth model with grid blocks at millimeter scale. We recommend a hierarchical modeling approach to address this challenge. At field scale, earth models are built to capture geological features and heterogeneities in high but still practical grid resolutions. For each facies or rock type of the field-scale model, high- resolution meter-scale “conceptual” models are built with millimeter-scale grid blocks to capture representative fine-scale bedding geometries and heterogeneities in various environments of deposition, bridging the gap from subcore scale to the size of a field-scale simulation grid block. Upscaling is then used to preserve the smaller-scale flow dynamics of various rock types in field-scale simulations. Here, future work is needed to (1) refine, improve, and validate the hierarchical modeling approach; (2) build libraries of fine-scale bedding models for facies in various environments of deposition; (3) quantify multiscale capillary heterogeneity effects under subsurface uncertainties; (4) gain learning from different storage formations; and (5) establish best practices that balance accuracy and computational speed.

Capillary heterogeneity↗
DOE OSTI2021

Local structure analysis of low-temperature neutron pair distribution function coupled with molecular dynamics simulations of CH 4 and CO 2 hydrates from 2 to 210 K

CH 4 hydrates occur naturally and are an abundant potential fuel source with a corresponding risk of potent greenhouse gas release, due to their stability conditions at low temperature and high pressure. Byproduct CO 2 can be exchanged with CH 4 in these natural deposits and can potentially stabilize the hydrates at higher temperatures. CH 4 , CO 2 , and mixed CH 4 -CO 2 hydrates are studied with in situ neutron pair distribution function experiments from 2 to 210 K to investigate the impact of varying the CH 4 -CO 2 guest composition in the gas hydrate structure. These experiments combined with Reverse Monte Carlo analysis allow for the characterization of intermolecular CH 4 and CO 2 interactions with the water molecules which form the hydrate lattice and how they impact the local structure of the lattice itself. Results indicate that when CH 4 and CO 2 co-occupy the hydrate, the host is more strongly distorted than in the pure CH 4 and CO 2 hydrates, but this becomes less defined with increasing temperature. The presence of CO 2 in mixed hydrate increases the stability range and creates a barrier for CH 4 to completely leave the structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Economic and operational investigation of CO 2 sequestration through enhanced oil recovery in unconventional reservoirs in Colorado, USA

The ongoing CCUS commercial projects are highly relied on the support of government incentives due to massive capital investment. Here, this study analyzes the economics of carbon capture utilization and sequestration (CCUS) projects, shows a state-wide CCUS deployment exercise, followed by simulation results of enhanced oil recovery (EOR) based CO 2 storage in unconventional reservoirs. The comprehensive economic analysis of capture, transportation, sequestration costs, enhanced 45Q tax credits, and EOR revenue implies the practicality of CO 2 -EOR to offset the high CCUS costs. With the economics understanding, we study the top CO 2 sources, existing CO 2 pipelines, and sequestration sinks in the state of Colorado, USA. This paper next presents results from EOR simulation in one section of the unconventional Denver-Julesburg (DJ) Basin Niobrara and Codell reservoirs. The simulation model is based on a geological static model, incorporated with hydraulic fracture stimulation, history matched to production, and calibrated to the microseismic and time-lapse surface seismic data. The CO 2 -EOR simulation results show that oil production can be increased and more CO 2 stored with: a longer primary production period; the presence of a shut-in period; higher injection rates; and multi-well injectors. The modeling results show that about 7–10 Mscf of CO 2 will be stored when recovering 1 stb of EOR oil. By adding the enhanced oil revenue and the carbon credits together, it is estimated that the most economic case can generate $\$13$ MM when oil price is assumed to be $\$80$/stb, and the EOR oil revenue is 3.4 times greater than that generated from 45Q incentives. It corresponds to the scenario that a five-year primary production is followed by CO 2 injection into four wells with the sequence of injection (4 MMscf/day for 6 months), shut-in (6 months) and production (12 months). The best practices in this study will provide valuable insights for similar CCUS projects in other unconventional fields. Furthermore, this study defines a term named “Carbon Neutrality Index (CNI)” by comparing the amount of CO 2 stored with that burned by EOR oil. The CNI value of 0 indicates the enhanced oil is carbon neutral; a negative CNI value implies there is a net reduction in carbon emission. The 4-year huff-n-puff (HnP) simulation leads to a positive CNI value, indicating that the EOR oil generated in this process is not carbon neutral yet.

03 NATURAL GAS↗
DOE OSTI2023

Using high pressure solutions of polyfluoroacrylate and CO 2 to Seal cement cracks for improved wellbore integrity

Polyfluoroacrylate (PFA) is a hydrophobic and oleophobic polymer that is soluble in high pressure carbon dioxide (CO 2 ). In this study, the ability of PFA-CO 2 solutions to greatly reduce the apparent permeability of split or cracked Portland cement cylindrical samples is assessed. The apparent permeability values of confined samples were determined before and after treatment with PFA-CO 2 solutions. In four tests, PFA-CO 2 solutions were continuously displacing pure CO 2 from the cracked cement and the decrease in apparent permeability due to PFA adsorption and wettability alteration was monitored. The lowest apparent permeability cracked cement sample (81 nD) was completely sealed with a very small amount of solution. Samples with initial apparent permeabilities of 89 μD and 29.4 mD exhibited 92% and 99% reductions in permeability, respectively, before the experiments had to be stopped because of the excessively large increase in pressure drop. A 50% reduction in apparent permeability was observed with a 3.80 mD sample. Four other split cement samples (bound together with tape) with an initial apparent permeability in the 9.0–70 mD range were removed from the core holder and immersed in a PFA-CO 2 solution for 24 h to allow for PFA adsorption. Then the PFA-CO 2 solution was depressurized, allowing for the deposition of additional PFA from the solution within the crack as the pressure fell below the cloud point pressure of the PFA-CO 2 solution. These four samples were then confined again in a core holder and apparent permeability reductions of 29–93% were observed. Finally, results from these eight experiments indicates that the more substantial reductions in the nD – mD apparent permeability of the cracked cement correlated to lower initial crack permeability, higher PFA concentration, and slower injection rate of the PFA-CO 2 solution into the crack.

58 GEOSCIENCES↗
DOE OSTI2022

Supercritical, liquid, and gas CO 2 reactive transport and carbonate formation in portland cement mortar

In this paper, we investigate carbonate formation and reactive transport rate in variably saturated portland cement mortars when high concentrations of gas, liquid, or supercritical CO 2 flow through their pore network. Xray computed tomography completed during CO 2 flow is used to quantify the microstructural evolution as the mortar carbonates. After in situ tests, higher resolution scans, thermogravimetric analysis, and desorption isotherm analysis are performed to further quantify microstructural changes. We found that at dry conditions supercritical CO 2 moves more rapidly through the pore space and precipitates more carbonates than liquid or gas CO 2 . However, at 50% degree of saturation (DOS) the CO 2 state did not affect the rate of transport in that each specimen exposed to a different CO 2 state carbonated within the first hour of CO 2 exposure. When the pore space is at 50 or 100% DOS, supercritical CO 2 did not react with hydration products more rapidly nor did it result in more carbonate formation during exposure compared to gas or liquid CO 2 . The amount of Ca(OH) 2 that contributes to CaCO 3 formation is correlated to the DOS. For the mortar composition analyzed, Ca(OH) 2 contributes to approximately 40% of the carbonates formed in the 50% DOS specimens and 15% in the 100% DOS specimens. In other words, as the amount of moisture in the pore space increases, phases other than Ca(OH) 2 contribute to more than 50% of the total CaCO 3 formed.

42 ENGINEERING↗
DOE OSTI2024

An experimental investigation on the CO 2 storage capacity of the composite confining system

Assuring secure containment of stored CO 2 is of paramount importance—for climate change mitigation, for permitting, and for reassuring the public. Regional seals, such as those sealing petroleum accumulations, have proven to be effective for securing CO 2 . However, the goal of permanent sequestration can also be satisfied with “composite confining systems” consisting of multiple, possibly discontinuous flow barriers that, in aggregate, create a system with very high permeability anisotropy and effectively retard the vertical migration of CO 2 . This study focuses on investigating the barrier characteristics necessary for effective containment of CO 2 , using both physical flow experiments and modified invasion percolation simulations. The simulations are calibrated to the physical experiments and are used to further extend the analysis. Results show that for a composite confining system, a) even barriers with low capillary entry pressure contrast to the underlying flow unit can divert rising CO 2 ; b) curved or anticlinal barrier topography can enhance CO 2 trapping; c) fining-upward gradations make little difference to barrier effectiveness or CO 2 retention; d) longer barriers retain more CO 2 regardless of barrier topography. Finally, field-scale simulations have demonstrated the importance of barrier length for increasing CO 2 storage capacity. Furthermore, the results presented can be used to inform the development of new screening criteria for characterization and effectiveness of composite confining systems.

58 GEOSCIENCES↗