CO2 Fluid Research Articles

Study of CO2 injection in a depleted oil reservoir using geomechanically coupled and non-coupled simulation models

This study seeks to understand CO2 injection into a depleted reservoir through multiphase fluid flow and geomechanical modeling simulations using field data. A comparison of the one-way geomechanically coupled and non-coupled models is presented. Results suggest that computed fluid pressure response and CO2 distribution in the reservoir are significantly influenced by reservoir geomechanical properties. The non-coupled model shows <50% of CO2 penetration distance and laterally shallower reservoir pressure changes compared to the coupled model after 53 days of injection. However, in the non-coupled model, CO2 concentration is significantly higher at short distances from the injection well compared to the coupled model. This reservoir behavior was attributed to the alteration in relative permeabilities caused by changes in geomechanical properties in the coupled model. Therefore, upon the availability of computing resources, one should use more computationally intensive but accurate models involving two-way-coupling. Finally, accurate determination of engineering properties and proper geological characterization is desirable for meaningful prediction models.

Modification of Li-Rich Layer-Structured Cathode Materials by Supercritical Co2 Fluid

Modification of Li-Rich Layer-Structured Cathode Materials by Supercritical Co2 Fluid

THERMOBAROGEOCHEMICAL EXPLORATION AND ASSESSMENT CRITERIA OF GOLD MINERALIZATION OF THE BALKA SHYROKA DEPOSIT (MIDDLE DNIEPER REGION)

A scheme of the staging and thermobaric regime of the formation of the Balka Shyroka deposit gold mineralization (Middle Dnieper megablock of the Ukrainian Shield) was constructed, and the sequence and thermobaric intervals of ore formation were determined. Mineral paragenesises are combined into four mineral associations that form a series of mineral complexes: pre-productive magnetite-quartz, productive polysulphide, which includes two productive gold-bearing associations (arsenopyrite-pyrite-quartz with gold and gold-sulphosalt) and post-productive carbonate (quartz-calcite mineral association). Gold-producing associations were formed in a rather narrow range of temperature and pressure changes of the ore-forming environment specific to its composition and aggregate-density state. This affected the phase typomorphism of the respective families of fluid inclusions. Carbon dioxide-water inclusions with different phase ratios are common: Г—РСО2—РН2О, РСО2—Г—РН2О, РСО2—РН2О, Г—РСО2. The most optimal temperature for homogenization of gas-liquid inclusions (according to the first type) is 210-290 °С. In minerals, there are families of two-phase and one-phase CO2 fluid inclusions with wide variations in its density (from 0.65 to 0.87 g/cm3) and homogenization into the liquid phase. These typomorphic features are thermobarogeochemical search criteria and evaluation signs of gold mineralization. Equally important is the definition of the paleotemperature gradient and the spatial extrapolation of its change with depth, which makes it possible to calculate the vertical extent of mineralization, the level of its erosional section, and the depth of thinning out.

U-Pb age and ore mineralization of dike lamprophires of the Roсa Islands (Wilhelm Archipelago, West Antarctica)

The dike of lamprophyres of the Roсa Islands chemically correspond to the basic rocks of the calc-alkaline series with high magnesian #mg 0.56. They have an increased content of Y (41.6 ppm) and Yb (11.5 ppm), which indicates the absence of garnet in the magmatic source. Rare earth elements are weakly differentiated — (La/Yb)N = 3.64). A deep negative European anomaly is distinguished — Eu/Eu*=0.36, which is probably due to the fractionation of plagioclase in the crustal magmatic source. Polymetallic mineralization for copper (445 g/t), zinc (207 g/t), lead (123 g/t) and tungsten (28.7 g/t) was found. Zircon from lamprophyres is represented by two types of crystals. The first type – transparent yellowish-pink individuals with a pyramidal-prismatic habit. In terms of quantity, it dominates; the second type is the formation of a flat outline. Dimensions are usually 0.3—0.7 mm along the L4 axis. Crystals of the first type were selected for geochronological research. It was found that the lamprophyre zircon contains very little lead, and a significant part of it is the lead isotope 204Pb. For this reason, age values for uranium-lead ratios of 238U/206Pb are more reliable. It was determined that the uranium-lead age of zircon from lamprophyres is within 50—60 Ma. Primary melt inclusions and less often mineral inclusions were found in zircon crystals. The former can sometimes occupy up to 30% of the crystal volume. Among the mineral inclusions, potassium feldspar, albite and potassium-sodium feldspar, apatite, and quartz were diagnosed. One primary inclusion of CO2 fluid was detected, the remaining inclusions are represented by primary crystallized melt inclusions. Rooting of the lamprophyre dyke is probably associated with the stress stresses experienced by the granodiorite plutons as a result of later tectonic movements.

Development of a technology for obtaining a polyphenolic biologically active additive from grape pomace for a wide range of applications

The research work considers the development of a technology for processing secondary raw materials of winemaking, which, due to preliminary preparation, passes into the category of enriched high-quality environmentally friendly grape raw materials. This study is carried out with the aim of obtaining concentrated high-quality polyphenolic biologically active extracts that can be used as a functional raw biomaterial for a wide range of products: healthy/sports nutrition, medical and preventive cosmetics, alcoholic and nonalcoholic drinks, and other types of special functional additives. The novelty of the development lies in the fact that at the initial stage, the enrichment of raw materials with target polyphenolic compounds is carried out using effective supercritical fluid CO2 extraction, followed by the use of the obtained AGP** extracts in the form of a finished product - a phytopreparation with inherent functional properties.

Boron concentrations and isotopic compositions in methane-derived authigenic carbonates: Constraints and limitations in reconstructing formation conditions

The boron content and isotopic composition (δ11B), of marine carbonates have the potential to constrain CO2 chemistry during carbonate growth conditions. However, obtaining and interpreting boron compositions from authigenic carbonates in geological archives present several challenges that may substantially limit their application. In particular, contamination from non-carbonate phases during sample preparation must be carefully avoided, and a variety of controls on boron composition during authigenic growth conditions must be evaluated. To advance understanding of the use and limitations of boron in authigenic carbonates, we present data and modelling results on methane-derived authigenic carbonate (MDAC), a by-product of microbially mediated anaerobic oxidation of methane, taken from three cold seep sites along the Norwegian margin. We present a novel sequential leaching method to isolate the boron signals from the micritic (Mg-calcite) and cavity-filling (aragonitic) MDAC cements in these complex multi-phase samples. This method successfully minimizes contamination from non-carbonate phases. To investigate the factors that could potentially contribute to the observed boron signals, we construct a numerical model to simulate the evolution of MDAC δ11B and B/Ca ratios over its growth history. We show that diagenetic fluid composition, depths of precipitation, the physical properties of sediments (such as porosity), and mineral surface kinetics all contribute to the observed boron compositions in the different carbonate cements. While broad constraints may be placed on fluid composition, the multiple competing controls on boron in these diagenetic settings limit the ability to place unique solutions on fluid CO2 chemistry using boron in these authigenic carbonates.

Extraction of Kaempferitrin and Astragalin from Justicia Spicigera by Supercritical Fluid Extraction and Its Comparison with Conventional Extraction

A study of supercritical fluid CO2 extraction of kaempferitrin (KM) and astragalin (KG) from Justicia spicigera (muicle) was conducted. A 33 Box-Behnken design was used to analyze the effects of pressure (200-300 bar), temperature (40-60° C), and co-solvent flow rate (0.5-1.0 mL/min). The highest KM and KG concentration were achieved at a pressure of 300 bar, a temperature of 60° C, and co-solvent flow rate of 1.0 mL/min (ethanol 99.5 %), with a constant CO2 flow rate of 5 mL/min and extraction time of 180 min. Under these conditions, the experimental values for KM and KG (115.08±2.81 and 56.63±9.02 mg/100 g of dry powder, respectively) were similar to those calculated by the models (109.0 and 44.07 mg/100 g of dry powder, respectively). The use of 70 % ethanol as co-solvent in the supercritical extraction process considerably improved the yields of KM and KG (562.71±156.85 and 79.90±18.03 mg/100 g of dry powder, respectively) compared to the 99.5 % ethanol extractions. The conventional extraction showed the highest yields of KM and KG (574.20±65.10 and 113.10±15.06 mg/100 g of dry powder, respectively) at 70° C and extraction time of 120 min. Adequate yields were achieved of KM and KG by supercritical fluid extraction compared with conventional extraction (98 and 70 %, respectively); therefore supercritical fluid extract of J. spicigera could be used in the development of functional foods, as well as its possible use in traditional medicine by the health professionals.

Pore changes of slickwater-containing shale under supercritical CO2 treatment

Application of liquid CO2-slickwater hybrid fracturing technology can significantly improve the energy-enhancing efficiency and fracturing fluid flowback efficiency of shale reservoirs. However, supercritical CO2 (ScCO2) fluid and slickwater are inevitably retained in reservoirs after fracturing, resulting in limited understanding of the changes of shale pore structure, further impacting the evaluation of the gas adsorption and transportation behaviors as well as CO2 sequestration capacity in shale reservoirs. Therefore, the influences of the ScCO2-slickwater coupling effect on shale pore structure was analyzed by using X-ray diffraction, low-pressure nitrogen gas adsorption (N2GA), mercury intrusion porosimetry (MIP), field emission-scanning electron microscopy (FE-SEM), and fractal analysis. After ScCO2-slickwater treatment, the calcite and albite contents decreased, while the quartz and clay minerals contents increased in shale. The increase in number of micropores and mesopores and the reduction in number of macropores were observed by a combination of N2GA and MIP, which led to the total specific surface area (TSSA) and total pore volume (TPV) of the shale enlarged, while the average pore size reduced. Meanwhile, the fractal dimensions calculated by N2GA (D1, D2) and MIP (D3) were raised, indicating that pore surface roughness and structural complexity were strengthened. D1, D2 and D3 can roughly reflect fractal characteristic of micropores (<3.5 nm), mesopores (3.5–50 nm) and macropores (>50 nm), respectively. Thus, D1 and D2/D3 can be used to evaluate the gas adsorption and flow behaviors of shale, respectively. By analyzing the control experimental results of ScCO2-water and He-slickwater treatment and the FE-SEM images, shale pore changes after ScCO2-slickwater treatment can be explained by CO2 extraction and dissolution, secondary mineral precipitation and polyacrylamide adsorption. After treatment, the increase of micropores and mesopores as well as TSSA and TPV makes the gas-adsorption capacity of shale improved, showing that the coupling effect of ScCO2-slickwater can not only improve shale gas productivity, but also benefit geological storage of CO2.

A potentially non-contact monitor method for CO2 at the pseudo-critical region using infrared spectrometer

Supercritical carbon dioxide (sCO2) Brayton cycle is a promising choice for thermal power generation with the advantages of high efficiency, compactness and low cost. There is a very sensitive part for monitor and control in the cycle, i.e. CO2 at the critical region, which affects the efficiency of compressor greatly and maybe brings safety problems due to the rapid and great changes in the properties of CO2 near the critical point. A non-contact measurement method is proposed to monitor the transient state of CO2 at various operating conditions using an infrared spectrometer. Experimental investigations were carried out to verify the adaptability of the method at dynamic processes in transcritical CO2 loop tests. We found the density change of CO2 fluid can directly impact the absorption spectrum near the wavelength of 3400 nm, which could serve as an efficient signal of CO2 state changes. In a steady state, a dramatic reduction of the density (− 70 %) and the absorption ratio (− 60 %) were observed between 30 and 34 ºC. In the dynamic processes, density-related scattering phenomena were observed near the pseudo-critical points, which strengthened the non-transmissive ratio (up to 0.95) of CO2 and gave a quick signal (<1 s) whenever abnormal condition occurred. Density stratification was further observed in the heating process at 32.5 ºC and 7.5 MPa, which was close to the critical point. Moreover, the gasification time was more than five times longer than the liquefaction time, which caused a stronger scattering phenomenon in depressurization processes. This work is expected to serve as the foundation work of the potentially non-contact monitor in the sCO2 Brayton cycle or other applications.

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).

Mineralogical and geochemical changes in conglomerate reservoir rocks induced by CO2 influx at Mih\xe1lyi-R\xe9pcelak natural analogue, NW-Hungary

A temporary solution to massive anthropogenic CO2 emissions can be the capture of industrial CO2 from flue gas and sequestering it in geological formations. For safe and effective storage of CO2, interaction processes in the rock-pore fluid–CO2 system should be known. Investigation of natural CO2 accumulations provides valuable examples to what physical and chemical effects could be expected during CO2 influx at future CO2 storage sites. One of the key controlling factors of the processes occurring in natural CO2 reservoirs is the lithology of the storage rocks, which is primarily determined by the formation conditions of these rocks. In this respect, the lithologies of individual CO2 accumulation areas influence the processes between the host rock, the pore fluid, and the CO2 in different ways. In the current study, we focus on a well-studied natural CO2 storage reservoir, namely the Mihályi-Répcelak area, NW Hungary. We provide insight into the so far unstudied conglomerate reservoirs that represent a stratigraphically deeper reservoir unit with significantly different lithology and pore water compositions compared to the sandstone reservoirs. Our results indicate that dawsonite /NaAlCO3(OH)2/ formation also affected the conglomerate reservoirs, which indicates that at least part of the CO2 could be trapped in mineral form. An important role of salinity in reducing the CO2 mineral trapping capacity of the storage system is also demonstrated. Furthermore, H isotope analysis of diagenetic kaolinite was applied to trace the origin of the pore water that was present during the rock formation. Based on the data, dawsonite formation was induced by the flux of meteoric water that infiltrated during a warm and humid period and mixed with ascending CO2.

Hydrosilylation of High Porosity Porous Silicon with 1-Hexene in Supercritical CO2 Fluid

Hydrosilylation of organic groups on hydrogen-terminated porous silicon (PSi) enhances its luminescence stability. Increasing PSi porosity improves its luminescence efficiency. However, for as-formed PSi layers with higher porosity than 75%, it is very difficult to preserve its fine structure during air-drying. Here, a process of both drying and hydrosilylation of highly porous silicon in ambient supercritical fluid was developed. 1-hexene was used for the hydrosilylation. Supercritical fluid hydrosilylation of PSi with porosity of 80% was achieved. The effects of the process were evaluated in terms of Fourier transform infrared spectroscopy. Stable photoluminescence of high porosity PSi was also obtained.

From peridotite to fuchsite bearing quartzite via carbonation and weathering: with implications for the Pb budget of continental crust

Extensive carbonation of peridotite results in listvenite, a rock composed of magnesite and quartz. At Gråberget, Røros, SE-Norway, a variably serpentinized peridotite body, surrounded by the Røros schists, a former abyssal sediment displays all stages of transformation of peridotite to quartzite. In this paper we record the sequence of steps in this process by combining the observation of mineral assemblages, textural relationships and geochemistry, and variations in Pb isotopic compositions. Initial serpentinization, a stage that also involved an enrichment in fluid-mobile elements (Pb, Sb and As), was followed by carbonation through CO2 fluids that formed soapstone, and eventually listvenite. The listvenite grades by decreasing amounts of carbonates into fuchsite bearing quartzite. The carbonates dissolved during supergene alteration and formed pores coated with oxides of Fe, Mn and Ni resulting in a brown rock color. The quartzite displays porous stylolites enriched in Pb, As and Sb and fuchsite with porous chromite grains as the only relicts of the original mineralogy in the peridotite. The dissolution of the carbonate occurred at oxidizing conditions at temperatures below 150 °C, where the solubility of magnesite is higher than that of quartz. Formation of quartzite from peridotite is supported by low REE contents and lack of zircons in the two rock types. The transformation involved enrichment of Pb, coupled with the elimination of Mg and enrichment of Si. This chemical fractionation and selective transfer of elements to the continents is an important mechanism and needs to be taken into account in models of continental evolution.

The Corrosion Behavior of N80 Steel in Multiple Thermal Fluid Environment Containing O2 and CO2

The corrosion behavior of N80 steel in Multiple thermal fluid environment containing O2 and CO2 was analyzed by Scanning Electron Microscopy (SEM), Energy-dispersive Spectrometry (EDS) and X-ray Diffraction (XRD) techniques. The results showed that, the corrosion products formed on N80 steel showed double layer structure. The outer layer are loose and porous, providing little protection. The inner layer are mainly FeCO3 crystals, and a small amount of Fe2O3 and FeOOH composition. The formation of Fe oxide on the inner layer of the film destroyed the integrity of the inner layer, resulting in localized corrosion. During the development of pitting, Cl− is enriched only at the tip of the pitting hole, which is the main cause of pitting corrosion and eventually leads to the formation of dendritic localized corrosion. The difference between internal and external potentials, the O2 concentration and the decrease of pH in the pitting holes combined to increase the corrosion process.

Control effect of fracture system on fluid migration, chemical reaction, and carbon dioxide storage

Carbon dioxide (CO2) injection alters a reservoir’s original equilibrium, leading to gas–liquid–solid reactions within the reservoir, resulting in mineral dissolution and precipitation affecting the reservoir’s physical properties. Because of their good permeability, faults are critical in fluid dredging and dominant channel formation. The characteristics of faults, including their width and strata length, directly affect the path, distance, and range of fluid migration and exert further control on the trend of water–rock–gas geochemical reactions. This study focused on the control effect of the fracture system on the migration, reaction, and storage of supercritical CO2. The faulted Cretaceous reservoir in the Kela-2 gas field of the Tarim Basin was selected as the study formation, and 10 heterogeneous profile models were established using multiphase-flow, solute-transport numerical simulation. The differences in fluid migration and reaction ranges under different fracture lengths, fracture widths, fracture physical properties, and CO2 injection rate conditions were examined. The real-time changes in profile porosity were quantitatively determined, and the control effect of the fracture system on reservoir development was analyzed. The results showed that CO2 fluid entering the formation migrates primarily along the fault. Under the condition of a wider fracture, the fracture’s fluid accumulation and reaction range increase, the degree of acidification is weak, and the ultimate porosity increase is small. When the fracture extends into the reservoir over a greater distance, fluid migrates over a greater distance, and the effect on both sides of the fracture is weak because of less fluid accumulation. Similarly, a higher injection rate causes a longer migration, producing a thin and long injection region similar to that of a long fracture. Better fracture properties result in a more obvious dredging effect. When the fracture’s permeability is insufficient, the injected fluid accumulates at the bottom of the fault, and eventually, only the porosity at the base of the fault changes significantly. In conclusion, the fracture system plays a very important role in controlling fluid migration, reaction, and reservoir development through induced reactions, and different fracture conditions lead to different reservoir development conditions.

Optimized production and enrichment of α-linolenic acid by Scenedesmus sp. HSJ296

The essential fatty acid α-linolenic acid is vital for human physiology and health. The green alga Scenedesmus sp. HSJ296 can accumulate large amounts of α-linolenic acid. In this work, we optimized the fermentation of Scenedesmus sp. HSJ296 in a 50-L fermenter, resulting in a biomass productivity of 3.12 ± 0.45 g L−1 d−1. We then extracted lipids from the biomass by supercritical fluid CO2 extraction with 95% ethanol as entrainer, achieving a lipid extraction rate as high as 73.47 ± 4.28%. After decolorization and enrichment by lipase hydrolysis, and low-temperature solvent crystallization, the content of unsaturated fatty acids in the lipid fraction from the biomass was enriched up to 92.5 ± 1.2%, with α-linolenic acid accounting for 62.6 ± 0.9%. The saturated fatty acids mainly consist of palmitic acid (C16:0, 3.1 ± 0.1%) and stearic acid (C18:0, 0.9 ± 0.1%). The remaining saturated fatty acid fraction, with relatively higher saturated fatty acid content, can be used as raw material for biodiesel production. Overall, we established an optimized α-linolenic acid production process that provides an important theoretical and technical basis for microalgae-based production of high-value lipids.

Experimental Study on the EOR Performance of Imbibition and Huff and Puff in Fractured Tight Oil Reservoirs

AbstractInjection of imbibition fluids or CO2 during hydraulic fracturing is an effective stimulation method for tight oil reservoirs. Selecting appropriate agents is significant to optimize the integrated scheme of fracturing and production in tight oil reservoirs. In this study, a series of lab experiments, including spontaneous imbibition, dynamic imbibition, and huff and puff, were carried out using real tight cores, water absorption apparatus, and core flooding equipment. The EOR performances of imbibition fluids and CO2 in fractured tight cores were compared. The mass transfer of imbibition fluids and CO2 in tight oil reservoirs and its influence on the sweeping volume and EOR mechanisms were discussed. The results show that (1) the spontaneous imbibition rate of imbibition fluids in tight cores is slow, and the oil recovery factor by spontaneous imbibition in cracked cores is relatively high, up to 13.42%. (2) In the dynamic imbibition experiments, the final oil recovery by CO2 injection was significantly higher than that by injecting imbibition liquids. Because of the excellent miscibility effect of CO2, oil production by CO2 injection mainly occurred in the primary displacement stage. Comparatively, the EOR effect of imbibition fluids mainly played its role during production after well shut-in, which can increase the oil recovery factor by 7.35%-11.64%. (3) The influence of the huff and puff mode of CO2 on EOR performance is greater than that of imbibition fluids due to its more sensitive compressibility and mass transfer rate. Generally, a high oil recovery factor can be obtained if the depletion production is conducted first, and a huff and puff operation is followed. (4) Comprehensively understanding the mass transfer characteristics of CO2 and imbibition fluids in tight oil reservoirs can guide the fracturing parameter design, such as the order of fracturing fluid slugs, the optimal soak time, and fracture spacing.

Thermodynamic Analysis of Reactions of CO2 Fluid with Garnet and Clinopyroxene at 3–6 GPa

Thermodynamic Analysis of Reactions of CO2 Fluid with Garnet and Clinopyroxene at 3–6 GPa

Analytical and numerical modeling for the assessment of CO2 storage in the Pariñas geological formation - Talara, Peru

This research evaluates the CO2 storage capacity of the Pariñas Formation belonging to the Talara basin in Peru through analytical modeling based on mass balance equations and numerical modeling using IMEX CMG. Pariñas Formation has several depleted hydrocarbon reservoirs that presents favorable conditions for CO2 geological storage. It has an average porosity of 17.6% and a permeability of 640 mD in the horizontal direction consisting of sandstones with interspersed lutites layers. The study evaluates the depleted Bellavista oil deposits involving CO2 storage capacity estimation with CO2 and reservoir fluid (oil and water) interaction. It involves numerical modeling based on the reservoirs properties and CO2 injection simulation not exceeding the fracture pressure of the reservoir rock. This approach is the first one carried out in Peru and provides the chance to evaluate the CO2 storage capacity in a hydrocarbon reservoir in this part of the world, as a strategy to mitigate future global change impacts. The results indicate a storage capacity of 35.37 million tons of CO2, approximately. Besides, the sandstone reservoir of the Pariñas geological formation has adequate characteristics to serve as a CO2 storage reservoir. C30+ pseudo component shows greater sensitivity in its properties (temperature and critical pressure) adjusting the fluid properties with the experimental data (saturation pressure, viscosity and minimum miscibility pressure).

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.