Supercritical CO2 Exposure Research Articles

Effects of the Supercritical CO2 Exposure Duration on Coal Permeability and Microstructural Changes

Effects of the Supercritical CO2 Exposure Duration on Coal Permeability and Microstructural Changes

The impact of supercritical CO2 exposure time on the effective stress law for permeability in shale

Carbon dioxide (CO2) sequestration in shale formations is regarded as an effective approach for reducing CO2 emissions. Permeability is critical for CO2 geological sequestration as it impacts migration of CO2 in shale formations. The effective stress coefficient for permeability (χ) scales the relative influence of pore pressure on permeability compared to confining pressure. This study examined the changes in χ of dry and wet shale samples with different times of supercritical CO2 (ScCO2) exposure. The results suggest that, as ScCO2 exposure time increases from 0 to 40 days, the χ of dry shale increases from 0.8304 to 0.9563, and that of wet shale increases from 0.8379 to 1.0134. Wet shale exhibits a greater increase in χ than dry shale for the same exposure time. These changes in χ may result from CO2-shale interaction that converts smaller-sized pores in shale into larger-sized pores, based on nuclear magnetic resonance (NMR) measurements. Furthermore, the presence of water intensifies the response of shale to ScCO2, thereby enhancing this transformation. Our findings provide insights into the accurate prediction of shale permeability evolution during CO2 storage, and can assist in optimizing CO2 injection strategies as well as evaluating the potential for CO2 sequestration.

Coal microstructural and mechanical alterations induced by supercritical CO2 exposure: Role of water

Injection of CO2 into deep unminable coal reservoirs is regarded as an effective method to reduce greenhouse gas emissions. Coal seams with burial depth > 800 m are the potential reservoirs for CO2 sequestration, and CO2 is stored in the form of supercritical state. The interactions between supercritical CO2 (ScCO2) and coal are a complex process, which has influence on coal structures and strength. Recent studies are rarely reported regarding the impact of ScCO2-coal-water reactions on coal microstructures and mechanical strength. In this paper, comparative analysis was conducted on the microstructural changes and mechanical degradation of coal induced by ScCO2 treatment and ScCO2-water saturation. The results show that water has great influence on coal pore structure, functional groups, mineral compositions and mechanical properties during the reaction. ScCO2 saturation only triggers a small decline of 11.27–17.65% in aliphatic groups in coal, while approximately 62.75–85.92% of aliphatic groups are extracted by ScCO2-water. The largest hysteresis loops are found in samples saturated by ScCO2-water, followed by the specimens treated by ScCO2, illustrating that the complexity of coal pore structure is enhanced by ScCO2 interaction, and the presence of water can further increase the pore roughness. The UCS is reduced by < 13% after ScCO2 saturation on dry coal, but it is greatly decreased by 26.58–44.21% in the presence of water. In the process of interaction, water accelerates the hydrocarbon extraction and mineral dissolution to aggravate the degradation of coal strength. This work is conducive to understanding the process of CO2 geological sequestration.

Long-term supercritical CO2 exposure dependence of physicochemical properties and CH4 adsorbability of moisture-equilibrated coal matrices

ABSTRACT Further understanding into the impacts of supercritical CO2 fluid exposure toward CO2 storage and coalbed methane (CH4) recovery is significant to evaluate validity, stability, and safety of CO2-ECBM. For purpose of addressing the potential impacts, the long-term static interactions between supercritical CO2 fluid and moisture-equilibrated coal matrices with various degrees of coalification were conducted at 318.15 K and 12.00 MPa for 240 days in this study. Furthermore, the changes of the physicochemical properties dominating adsorbability of moisture-equilibrated coals due to the exposure were revealed. Ultimately, the impacts of the exposure toward CH4 adsorbability of moisture-equilibrated coals were addressed. Results indicate that the long-term supercritical CO2 exposure induces complex effects typically including organic matter extraction, mineral dissolution and formation, and matrix swelling to the coals, thereby further reducing the micropores within pore diameter ranges of 0.38–0.71 nm and 0.74–0.90 nm of the low-rank moisture-equilibrated coals, and slightly increasing those of 0.40–0.70 nm and 0.75–0.90 nm of the high-rank moisture-equilibrated coal. Additionally, the complex effects reduce the mesopores with pore diameter less than 8.00 nm for all the coal samples. Moreover, the exposure alters the surface chemistry of the coals. Particularly, the exposure increases the oxygen-containing functional groups typically comprising C-O, C=O, and -COOH of the low-rank moisture-equilibrated coals by 25.32–27.16%, and weakens the graphitization of the high-rank coal by 34.00%. Moreover, the induced synergistic effects decrease the number of pores with diameter less than approximately 8.00 nm of all the moisture-equilibrated coals. Furthermore, the CO2 exposure significantly reduces CH4 adsorption capacity of the moisture-equilibrated coal matrices indicated by the decreasing amplitude in absolute adsorption amount of 6.20–18.00%. Overall, the long-term supercritical CO2 exposure could favor CH4 production during CO2-ECBM. Future study should focus on in-situ characterization and accurate quantitative analysis on extraction, mineral dissolution and formation, and matrix swelling due to CO2 exposure, and distinguishment in the contribution of these effects to pores and functional groups of coals.

Impact of supercritical CO2 exposure time on the porosity and permeability of dry and wet shale: The influence of chemo-mechanical coupling effects

CO2 storage in shale formation is a potential way to reduce CO2 emissions for carbon neutrality. The variation of permeability in shale triggered by CO2-shale interaction plays an important role in CO2 sequestration. The effect of supercritical CO2 (ScCO2) exposure times (0, 10, 20, 30, 40 days) on the porosity and permeability evolution of dry and wet shale samples was investigated herein. Results show that the porosity and permeability of both dry shale and wet shale increased first and then decreased over exposure time, and there is an inflection point. The porosity and permeability evolution of shale is controlled by the chemical-mechanical coupling effects. The dissolution of mineral induced by ScCO2 exposure increases the porosity and permeability of shale. The mechanical weakening induced by ScCO2 exposure enhances the pores compressibility of shale, makes the porosity and permeability decrease at stressed condition. In the early stage, the chemical effect is dominant, after the time of inflection point, the mechanical weakening effect is dominant. The inflection time of wet shale is earlier than that of dry shale, indicating that the chemical effect dominant stage in wet shale is shorter than that in dry shale. This can be attributed to that the water promoted the chemical reaction and enhanced the weakening of mechanical properties, then shortened the chemical corrosion dominated stage. Our findings suggest that ScCO2-shale interaction can contribute to the decrease in porosity and permeability of shale with the increase of ScCO2 exposure time, and hence adversely affecting the shale gas recovery and the continue injectivity of CO2. Thus, the time dependent chemical-mechanical coupling effects should be considered in evaluating the shale gas production and CO2 storage capacity.

Effects of supercritical CO2 exposure on diffusion and adsorption kinetics of CH4, CO2 and water vapor in various rank coals

The physico-chemical effects caused by supercritical CO2 (ScCO2) exposure is one of the leading problems for CO2 storage in deep coal seams as it will significantly alter the flow behaviors of gases. The main objective of this study was to investigate the effects of ScCO2 injection on diffusion and adsorption kinetics of CH4, CO2 and water vapor in various rank coals. The powdered coal samples were immersed in ScCO2 for 30 days using a high-pressure sealed reactor. Then, the diffusion and adsorption kinetics of CH4, CO2 and water vapor in the coals both before and after exposure were examined. Results indicate that the diffusivities of CH4 and CO2 are significantly increased due to the combined matrix swelling and solvent effect caused by ScCO2 exposure, which may induce secondary faults and remove some volatile matters that block the pore throats. On the other hand, the diffusivities of water vapor are reduced due to the elimination of surface functional groups with ScCO2 exposure. It is concluded that density of the surface function groups is the controlling factor for water vapor diffusion rather than the pore properties. The unipore model and pseudo-first-order equation can simulate the diffusion and adsorption kinetics of CH4 and CO2 very well, but the unipore model is not capable of well describing water vapor diffusion. The effective diffusivity (De), diffusion coefficient (D) and adsorption rates (k1) of CH4 and CO2 are significantly increased after ScCO2 exposure, while the values of water vapor are decreased notably. Thus, the injection of ScCO2 will efficiently improve the transport properties of CH4 and CO2 but hinder the movement of water molecules in coal seams.

Nano- to macro-scale structural, mineralogical, and mechanical alterations in a shale reservoir induced by exposure to supercritical CO2

Considering the importance of carbon neutrality, UCCUS which is underground carbon capture, utilization, and storage has been widely adopted to mitigate climate change. Studies are being conducted to improve this process, however, there is still a lack of knowledge on the multiscale physicochanical alterations that the storage reservoirs may endure due to the long-term exposure to supercritical CO2 (ScCO2). These changes happen from nano- to macro-scale in mineralogy and pore structures which will impact mechanical and petrophysical attributes of the host rock. Since unconventional shale reservoirs have become the target of CO2-EOR and CO2 storage, it is imperative to understand the long-term impact of these alterations due to ScCO2 exposure. This study coupled experimental and theoretical modeling to investigate continuous nano- to macro-scale changes in mechanical, mineralogical, and structural alterations in the Middle Bakken by exposing samples to ScCO2 for 3, 8, 16, 30 and 60 days. Qualitative analysis of electron micrographs pre and post exposure confirmed certain minerals have evolved while image processing showed a quantitative change in pore structures. Moreover, nanomechanical changes pre and post exposure were inspected via nanoindentation method. Furthermore, we assessed how mineral content was impacted during the exposure using X-ray diffraction analysis. Next, we adopted two rock physics models based on mechanical and mineralogical observations to upscale mechanical properties to the macro scale. Analyses of the results indicate that long-term ScCO2 exposure induces mineral dissolution, precipitation and the development of fractures in the host reservoir. Further, CO2 induced alterations can lead to long-term macro-scale weakening causing a loss in mechanical integrity of the Middle Bakken by decreasing its elastic modulus (DS model = –33 %, MT model = -30 %) and increasing its Poisson’s ratio (DS model = +38 %, MT model = +32 %). Overall, this study can provide new insights for a better design and implementation of UCCUS projects in shale reservoirs, most especially in the Middle Bakken and other similar formations, where a lack of understanding of these variations and project planning could lead to potential CO2 leakages and environmental hazards.

Experimental study on the methane desorption-diffusion behavior of Longmaxi shale exposure to supercritical CO2

Desorption-diffusion behaviors of CH4 in shale after supercritical CO2 (ScCO2) injection are closely related to CO2 enhanced shale gas recovery (CO2-ESGR). A self-developed gas desorption test system was used to measure the desorption kinetics of CH4 in shale collected from Sichuan Basin at different ScCO2 exposure pressures (8, 12, 16 MPa) and temperatures (40, 60, 80 °C), and the low-pressure N2 adsorption was performed to evaluate the variations of pore structure of shale. Results indicate that the desorption kinetics curves of CH4 in shale exhibit typical Langmuir characteristics under different desorption pressures, and the kinetics data were fitted by unipore and bidisperse diffusion models, manifesting that the diffusion of CH4 in the shale samples are dominated by macroporous channel (>95%). With increasing desorption pressure, the desorption capacity of CH4 in shale (nde) increased, while the diffusion coefficient of CH4 in shale (D) decreased. Additionally, the nde and D increased after ScCO2 exposure, and exhibited a slight exposure pressure and temperature dependence, which is mainly caused by the decrease of specific surface area and the widening of microstructure in shale, implying that the ScCO2-shale interaction can promote the desorption-diffusion of CH4 in shale. This study provides a theoretical reference for CO2-ESGR.

Impact of Supercritical Co2 Exposure Time on the Permeability of Dry and Wet Shale: The Influence of Chemo-Mechanical Coupling Effects

Impact of Supercritical Co2 Exposure Time on the Permeability of Dry and Wet Shale: The Influence of Chemo-Mechanical Coupling Effects

Influence of supercritical CO2 exposure on water wettability of shale: Implications for CO2 sequestration and shale gas recovery

The wettability of reservoir rocks is considered to be closely related to fluid distribution and CO2 geo-storage (CGS) security after injecting CO2 into reservoir. To investigate the influence of supercritical CO2 (ScCO2) injection on water wettability of shale, a sessile drop method was used to measure water contact angles of shale samples collected from Sichuan Basin (marine) and Ordos Basin (continental) at different ScCO2 exposure time and pressure. In addition, X-ray diffraction (XRD) and low-pressure N2 adsorption (LP-NA) were performed to evaluate the variations of mineral compositions and pore structure of shale. Results indicate that shale-water contact angles generally increased (from 22.74% to 43.94%) after ScCO2 exposure, which is primarily caused by the decrease of clay minerals and carbonates in shale. The water wettability of shale weakened after ScCO2 exposure, indicating that the interaction force between shale and water molecules changed, which may have reduced the resistance of water to flow in pores and fractures of shale, inferring that the alterations of shale water wettability after ScCO2 injection is beneficial to gas seepage in pore channels, but may exert a negative influence on CGS stability. This study provides a theoretical reference for CO2 sequestration and CO2-enhanced shale gas recovery (CS-ESGR).

Influence of sequestered supercritical CO2 treatment on the pore size distribution of coal across the rank range

The influence of supercritical CO2 (SC-CO2) fluids on pore structure characteristics of coal plays a vital role in geo-sequestration of CO2 into deep coal seams. Changes in coal pore structure and mineral content after exposed to SC-CO2 fluids are quantitatively evaluated by N2/CO2 adsorption and X-ray diffraction (XRD) for a lignite, bituminous and anthracite coals. The SC-CO2 exposure has a notable effect on coal pore distribution. Affected by SC-CO2, the micropore volume within coal is reduced by 12.6 to 34.8%, while both the average pore diameter and macropore volume are remarkably increased. XRD analysis shows that no newly-formed mineral compositions were detected in treated coals, but the mineral content is altered. As the main carbonate minerals of coal, both calcite and dolomite are consumed during SC-CO2 treatment. Due to the strong extraction capacity for small organic molecules, the influence of SC-CO2 is related to coal rank, and the largest increment in macropore volume is observed in lignite. The greatest reduction of micropore volume is identified in anthracite treated sample, indicating that SC-CO2 has the most impact on micropores in high-rank coal. Mineral dissolution likely accounts for this reduction in micropore contribution by increasing mesopores and macropores.

Surface wettability alteration of shales exposed to CO2: Implication for long-term integrity of geological storage sites

Surface wettability is a key factor controlling the CO2 seal capacity and defines the CO2 storage potential. Limited studies have addressed the shale/water wettability behavior during CO2 injection, thus considerable attention is needed to understand this concept. In this paper, an ample number of supercritical CO2 exposure experiments were conducted to evaluate the alteration of shale/water contact angles. Different types of shales with various mineralogy from Eagle Ford, Wolfcamp, and Mancos fields, were exposed to SCCO2 at different durations, pressures, and temperatures. Shale mineralogy and surface were analyzed using X-ray diffraction and scanning electron microscope. The results indicated a strong relationship between mineral composition and the alteration in shale/water wettability. Clay-rich shales displayed a possible turn in wetting behavior to CO2-wet with extending the SCCO2 treatment time and increasing the treatment pressure, caused by SCCO2 dissolution of clay and carbonate minerals. While the wettability of high-quartz contents shales remained strongly hydrophilic after various SCCO2 treatment conditions. Increasing the temperature accelerated the CO2/shale interactions, and a minor effect was observed on the shale hydrophilicity. Increasing the cohesive energy density of CO2 promotes a favorable CO2 wetting environment, which reduced the hydrophilicity of the surface and reduces the surface energy. In conclusion, shales with high quartz contents exhibit strong water wetting behavior after SCCO2 treatment, which leads to better sealing capacity, more efficient integrity of geological storage sites, and higher potential for CO2 containment.

Investigation of adsorption kinetics of CH4 and CO2 on shale exposure to supercritical CO2

The adsorption kinetics behaviors of CH4 and CO2 on shale are closely related to CO2 sequestration and enhanced shale gas recovery (CS-ESGR). To investigate the influence of supercritical CO2 (ScCO2) exposure on adsorption kinetics behaviors of CH4 and CO2 on shale, X-ray diffraction analysis, low-pressure N2 adsorption and adsorption kinetics experiment of CH4 and CO2 were conducted on raw and ScCO2-treated (10 day/16MPa/40 °C) shale collected from the Ordos Basin. Adsorption rates of CH4 and CO2 by shale were fitted by different adsorption kinetics models, and results indicate that Bangham adsorption (BA) model exhibits a better fitting effect (R2＞0.99) than Pseudo-first-order (PFO) and Pseudo-second-order (PSO) kinetic model and Elovich adsorption (EA) model. After ScCO2 exposure, the adsorption rate of CH4 and CO2 by shale decreased, which may be mainly caused by the decrease of high energy adsorption sites of shale. In addition, the adsorption rate of CO2 by shale is significantly higher than that of CH4, and the influence of pressure on the adsorption rates of CH4 and CO2 is remarkably different, suggesting that the CS-ESGR project should be divided into three stages: Fracturing-Recovery, Replacement-Recovery-Sequestration, and Replacement-Sequestration-Recovery. This study provides a reference for future optimization design of CS-ESGR.

The carburization behavior of alloy 800HT in high temperature supercritical-CO2

The contribution of high temperature supercritical-CO2 (S-CO2) exposure (650 °C for 1000 h) on the carburization behavior of Alloy 800HT was studied. For comparison, Alloy 800HT specimens were also exposed to air and vacuum environments. The S-CO2 exposed specimens showed carbon-accumulated layer at the oxide-matrix interface. All specimens showed subsurface carbide precipitation but it was more pronounced for the S-CO2 exposed specimen, suggesting inward carbon diffusion from the carbon-accumulated layer at oxide-matrix interface. The pronounced subsurface carbide precipitation for the S-CO2 exposed specimens resulted in much increased hardening and reduction in ductility. Thus, we clearly identified that S-CO2 exposure caused the formation of the interfacial carbon-accumulated layer and more subsurface carbide precipitates, and resulting in additional hardening and reduction in ductility for Alloy 800HT.

Effect of supercritical CO2 on salt water corrosion and wear resistance of bismaleimide coating filled with organophilic montmorillonite clay

Ceramic filled polymer coatings have been shown to increase the salt water corrosion protection and wear resistance of metallic substrates. With an increase in natural and anthropogenic CO2 use as an enhanced oil recovery method paired to conventional brine-based recovery, termed ‘water after gas’ the impact of corrosion remains unknown. In this paper, we investigate the effect of salt water corrosion in a filled and unfilled coating before and after supercritical CO2 exposure. Corrosion performance is evaluated using electrochemical Tafel and impedance spectroscopy. Wear was measured using a pin on disk testing. After exposure to CO2, the corrosion performance of filled and unfilled systems were similar while the wear resistance of the filled coating was superior.

The effects of long-term supercritical CO2 exposure on Zululand Basin core samples

Carbon dioxide (CO2) sequestration in geological formations is a viable solution for ensuring coal-based energy supply whilst reducing CO2 emissions. The variation in the microstructure and composition of geological formations before and after CO2 storage plays a significant role in CO2 sequestration. Three core samples obtained from the Zululand Basin in South Africa were exposed to supercritical CO2 (ScCO2) in the presence of water under typical hydrothermal conditions (175 bar, 70 °C) for up to 2 months. The samples were characterized pre- and post-treatment using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), low pressure nitrogen (N2) adsorption and low pressure CO2 adsorption. Physical and chemical structural changes were observed in all three samples after treatment, to varying degrees. Mineral alterations were observed in the three samples, including plagioclase and calcite dissolution/precipitation and quartz composition changes. Dissolution of organic components and surface chemistry alterations were found in two of the core samples. Increases in pore volume, surface area and CO2 adsorption capacity were observed in all studied samples after CO2 treatment.

Influence of Supercritical CO &lt;sub&gt;2&lt;/sub&gt; Exposure on Water Wettability of Marine and Continental Shale

To investigate the influence of supercritical CO2 (ScCO2) exposure on water wettability of shale, a systematic contact angle experiments considering ScCO2 exposure time and pressure were conducted on shale samples collected from Sichuan Basin (marine) and Ordos Basin (continental), respectively. In addition, X-ray diffraction analysis and low-pressure N2 adsorption were performed to evaluate the variations of mineral compositions and pore structure of shale. Results indicate that the tested shale samples are both hydrophilic rocks, and the shale-water contact angles generally increased with increasing ScCO2 exposure time and pressure, which is primarily caused by the the decrease of clay minerals and carbonates in shale. The water wettability of shale weakened after ScCO2 exposure, indicating that the interaction between shale and water molecules decreased, which may reduce the resistance of water to flow in pores and fractures of shale. Accordingly, it can be inferred that the alteration of shale water wettability after ScCO2 injection is beneficial to the seepage of gas in shale pore channels, but may exist a negative influence on the stability of CO2 geological sequestration. This study provides a theoretical reference for CO2 sequestration and CO2-enhanced shale gas recovery (CS-ESGR).

Supercritical CO2 Exposure-Induced Surface Property, Pore Structure, and Adsorption Capacity Alterations in Various Rank Coals

Carbon dioxide (CO2) has been used to replace coal seam gas for recovery enhancement and carbon sequestration. To better understand the alternations of coal seam in response to CO2 sequestration, the properties of four different coals before and after supercritical CO2 (ScCO2) exposure at 40 °C and 16 MPa were analyzed with Fourier Transform infrared spectroscopy (FTIR), low-pressure nitrogen, and CO2 adsorption methods. Further, high-pressure CO2 adsorption isotherms were performed at 40 °C using a gravimetric method. The results indicate that the density of functional groups and mineral matters on coal surface decreased after ScCO2 exposure, especially for low-rank coal. With ScCO2 exposure, only minimal changes in pore shape were observed for various rank coals. However, the micropore specific surface area (SSA) and pore volume increased while the values for mesopore decreased as determined by low-pressure N2 and CO2 adsorption. The combined effects of surface property and pore structure alterations lead to a higher CO2 adsorption capacity at lower pressures but lower CO2 adsorption capacity at higher pressures. Langmuir model fitting shows a decreasing trend in monolayer capacity after ScCO2 exposure, indicating an elimination of the adsorption sites. The results provide new insights for the long-term safety for the evaluation of CO2-enhanced coal seam gas recovery.

Polymer of Intrinsic Microporosity (PIM-1) Membranes Treated with Supercritical CO2

Polymers of intrinsic microporosity (PIMs) are a promising membrane material for gas separation, because of their high free volume and micro-cavity size distribution. This is countered by PIMs-based membranes being highly susceptible to physical aging, which dramatically reduces their permselectivity over extended periods of time. Supercritical carbon dioxide is known to plasticize and partially solubilise polymers, altering the underlying membrane morphology, and hence impacting the gas separation properties. This investigation reports on the change in PIM-1 membranes after being exposed to supercritical CO2 for two- and eight-hour intervals, followed by two depressurization protocols, a rapid depressurization and a slow depressurization. The exposure times enables the impact contact time with supercritical CO2 has on the membrane morphology to be investigated, as well as the subsequent depressurization event. The density of the post supercritical CO2 exposed membranes, irrespective of exposure time and depressurization, were greater than the untreated membrane. This indicated that supercritical CO2 had solubilised the polymer chain, enabling PIM-1 to rearrange and contract the free volume micro-cavities present. As a consequence, the permeabilities of He, CH4, O2 and CO2 were all reduced for the supercritical CO2-treated membranes compared to the original membrane, while N2 permeability remained unchanged. Importantly, the physical aging properties of the supercritical CO2-treated membranes altered, with only minor reductions in N2, CH4 and O2 permeabilities observed over extended periods of time. In contrast, He and CO2 permeabilities experienced similar physical aging in the supercritical treated membranes to that of the original membrane. This was interpreted as the supercritical CO2 treatment enabling micro-cavity contraction to favour the smaller CO2 molecule, due to size exclusion of the larger N2, CH4 and O2 molecules. Therefore, physical aging of the treated membranes only had minor impact on N2, CH4 and O2 permeability; while the smaller He and CO2 gases experience greater permeability loss. This result implies that supercritical CO2 exposure has potential to limit physical aging performance loss in PIM-1 based membranes for O2/N2 separation.

Effect of supercritical CO2 exposure on the high-pressure CO2 adsorption performance of shales

The interactions between shales and supercritical carbon dioxide (ScCO2) as well as the influence of these interactions on the pore structure and the surface functional groups play a key role in long-term CO2 geological sequestration. To investigate the effect of ScCO2 treatment on the performance of high-pressure CO2 adsorption, three shale samples selected from different formations were treated with ScCO2 in a geochemical reactor to simulate the in situ geological sequestration process. The high-pressure adsorption behaviors of CO2 on untreated and ScCO2-exposed shale samples were measured by gravimetric method at 45 °C and pressures up to 18 MPa. Characterization methods included scanning electron microscope (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), low-pressure gases adsorption (LP-GA), element analysis (EA) and X-ray photoelectron spectroscopy (XPS). The experimental results indicated that ScCO2 fluid could significantly alter the structural and physicochemical properties of shales, leading to the variations in high-pressure CO2 adsorption capacity of shales. The moisture and oxygen contents in the ScCO2-exposed samples were lower than those in the untreated samples. XPS analysis showed that the relative content of the organic oxygen-containing functional groups (CO, CO, OCO and COO−) in the raw shale samples decreased after the ScCO2 treatment. After long-term ScCO2 immersion, the maximum CO2 adsorption capacity of the shale samples exhibited a decreasing trend when compared to the raw samples, which was linked to the changes in the specific surface area of the micro- and mesopores as well as the oxygen-containing functional groups. The results obtained in this paper provide a basis for further evaluation of CO2 storage mechanisms.