CO2 Fluid Research Articles

Source and Generation Parameters of the Granitoid Melts of the Archean Charnockite–Enderbite Complex in Karelia, with Reference to the Pon’goma-Navolok Massif

The paper presents authors’ original detailed data on rocks of the Archean Pon’goma-Navolok charnockite−enderbite complex in northern Karelia. The rocks practically have not been modified and are preserved within a rigid block among Paleoproterozoic zones of ductile deformations and metamorphism. The geochemistry of the rocks and their isotope−geochemical features indicate that the protolith from which the enderbite melts of the main phase of the massif were derived may have been amphibolites. The enderbite melts were derived from these amphibolites under the effect of K2O-, Na2O-, and SiO2-bearing fluids; and the enderbites were subsequently charnockitized with the involvement of fluids enriched in K2O and SiO2. Physicochemical modeling indicates that the enderbite melt was derived from the amphibolite protolith at a depth of about 45 km (P = 14.8 kbar, T = 1030−1080°C) under the effect of saline H2O−CO2 fluid. Comparison of the P−T parameters of the granulite-facies metamorphism of the metabasites and the parameters under which the enderbite melts were derived indicates that Archean granulite-facies metamorphism in the Belomorian belt in northern Karelia was of contact but not regional nature and was induced by the high-temperature field of an emplaced enderbite massif. The orthogneisses hosting the Pan’goma-Navolok massif inherit geochemical features of the unsheared, ungneissose, and unmetamorphosed enderbites. This means that enderbites analogous to those of the Pan’goma-Navolok massif may have served as the protolith of some of the orthogneisses, and that enderbites may have been spread more widely in the Archean than the currently preserved single enderbite massifs.

Source and Generation Parameters of the Granitoid Melts of the Archean Charnockite–Enderbite Complex in Karelia, with Reference to the Pon’goma-Navolok Massif

—The paper presents authors’ original detailed data on rocks of the Archean Pon’goma-Navolok charnockite−enderbite complex in northern Karelia. The rocks practically have not been modified and are preserved within a rigid block among Paleoproterozoic zones of ductile deformations and metamorphism. The geochemistry of the rocks and their isotope−geochemical features indicate that the protolith from which the enderbite melts of the main phase of the massif were derived may have been amphibolites. The enderbite melts were derived from these amphibolites under the effect of K2O-, Na2O-, and SiO2-bearing fluids; and the enderbites were subsequently charnockitized with the involvement of fluids enriched in K2O and SiO2. Physicochemical modeling indicates that the enderbite melt was derived from the amphibolite protolith at a depth of about 45 km (P = 14.8 kbar, T = 1030−1080°C) under the effect of saline H2O−CO2 fluid. Comparison of the P−T parameters of the granulite-facies metamorphism of the metabasites and the parameters under which the enderbite melts were derived indicates that Archean granulite-facies metamorphism in the Belomorian belt in northern Karelia was of contact but not regional nature and was induced by the high-temperature field of an emplaced enderbite massif. The orthogneisses hosting the Pan’goma-Navolok massif inherit geochemical features of the unsheared, ungneissose, and unmetamorphosed enderbites. This means that enderbites analogous to those of the Pan’goma-Navolok massif may have served as the protolith of some of the orthogneisses, and that enderbites may have been spread more widely in the Archean than the currently preserved single enderbite massifs.

Geology, fluid inclusions and C−O−S−Pb isotopic compositions of the Chahmileh Pb-Zn deposit, Central Iran: Implications for ore genesis

AbstractThe Chahmileh Pb–Zn deposit, located northwest of the Central Iran Zone, is a sediment-hosted Pb–Zn deposit in the ‘Yazd-Anarak Metallogenic Belt’. It is hosted in Middle Triassic carbonate rocks and is mainly controlled by NW-trending faults. The main ore minerals are galena and sphalerite with minor chalcopyrite, pyrite, and quartz, dolomite, along with minor calcite and baryte as gangue minerals. Cerussite, hemimorphite, wulfenite, mimetite, smithsonite, malachite and iron oxy-hydroxides are the main non-sulphide ore minerals. The main styles of mineralization are vein-veinlet, breccia, disseminated and replacement in association with silicification and dolomitization. Microthermometry of fluid inclusions in dolomite and quartz indicates that the ore precipitated from a warm to hot basin-derived saline fluid. Dolomite samples have δ13CVPDB and δ18OVSMOW values of −0.99 to +1.99‰ and +20.74 to +25.48‰, respectively, and are plotted in the marine carbonate rocks field. These isotopic values suggest that CO2 in the hydrothermal fluids mainly originated from marine carbonate rock. The δ34S values range from +6.3 to +8.2‰ for galena, +5.9 to +6.2‰ for sphalerite, +1.4 to +3.4‰ for chalcopyrite and +15.0 to +17.4‰ for bayite are compatible with a predominant thermochemical sulphate reduction process, and with sulphur sourced from Triassic seawater. Galena samples have a homogeneous Pb isotopic composition that is indicative of a continental crustal reservoir as the main source of lead and probably for the other ore metals. Based on geology, mineralogy, texture and fluid characteristics, the Chahmileh deposit is classified as a carbonate-hosted Mississippi Valley-type deposit.

Qualifying Bismuth Plug Technology in Mozambique

_ Over the past 10 years, bismuth plugs have been used more often to solve complex downhole integrity issues and to permanently abandon wells, both on and offshore. As bismuth technology is relatively new to the market, it often needs to be qualified in-country before use on a larger scale. This is a significant barrier to the adoption of new technologies in general within the industry and not unique to the use of bismuth as a permanent sealing barrier. Bismuth and bismuth-based alloys have unique properties that allow them to be used as a sealing material that has the potential to change the industry. It has a specific gravity of 10 which means it is 10 times denser than water. In molten form it can displace any fluid in the wellbore. Not only is it dense but in its molten form it also has a viscosity like water, which means it can flow easily and through perforations, cracks, crevices, or any micro annuli without the need of any pumping equipment. The most interesting property however is its ability to expand on solidification. BiSN uses proprietary thermite heaters to melt bismuth-based alloys downhole, which then flow into the annulus through perforations or section milled windows taking the shape of volume they are filling up. The alloy on solidification then expands (like ice) which creates the gas-tight seal against the surface it is expanding. These alloys not only create a solid mechanical barrier but are also highly corrosion resistant to H2S, CO2, acids, and other wellbore fluid that might be present, thereby creating a barrier that can last forever or be classified as “eternal.” Compared to existing traditional sealing technologies, a bismuth plug requires a significantly shorter seal, resulting in less materials, section milling, and time needed for deployment. For example, a traditional cement plug might need to be hundreds of feet in length where a bismuth plug can be set at as little as 6 ft. Field Test—Context, Challenges, and Methodology In May 2023, BiSN was contracted to fulfill a rigless plug and abandonment (P&A) campaign for Sasol in Mozambique. Before proceeding, BiSN and Sasol worked together on a well in Mozambique to qualify BiSN bismuth technology as a permanent abandonment solution in the country. The well chosen for the seal test had several complicating factors including the need to set the seal in open hole through perforations and the thin caprocks located in the region. The overall goal of the field test was to isolate gas-bearing silt from shallower formations by forming an effective seal. To accomplish this, the bismuth plug was required to be set with a 10-m shale window identified by Sasol as a suitable location to set a regional seal to essentially restore the caprock. Previous explorations had revealed areas of patchy cement from earlier P&A attempts.

High-pressure melting in metapelites of a 2 Ga old subducted oceanic crust (Usagaran belt, Tanzania): implications from melt inclusions, fluid inclusions and thermodynamic modelling

Investigation of polymineralic melt inclusions preserved in garnet of eclogite-facies metapelites of the Usagaran belt, Tanzania, is of particular importance as these metapelites, intercalated in oceanic metabasites, document the rare case of partial melting at high temperatures in a subducted oceanic crust. With an age of 2 Ga the rocks represent one of the oldest oceanic crusts and confirm a subduction process already at Paleoproterozoic times. Partial melting probably was initiated by dehydration melting under the presence of a CO2-rich fluid phase. The melt is preserved in siliceous polymineralic inclusions, while CO2 locally reacted with the garnet host to form dolomite-quartz-kyanite inclusions. During this reaction, the REE spectrum of garnet is adopted by the dolomite. Furthermore, graphite inclusions in garnet must have precipitated from the CO2 fluid by reduction. The highly ordered graphite structure indicates a formation temperature of at least 700 °C. Rehomogenization experiments of the siliceous polymineralic inclusions yield a homogeneous melt of rhyolitic, peraluminous composition. Thermodynamic modelling enables to deduce a P–T path in accordance with high P–T conditions (minimum 2.0 GPa, 900 °C) where a partial melt formed due to phengite breakdown leading to the preserved peak mineral assemblage garnet, alkali feldspar, kyanite, quartz and rutile. A very fast uplift of the oceanic crustal rocks can be deduced from the occurrence of very finely exsolved metastable ternary feldspar and from the preserved prograde zoning in garnet.

Spatially resolved CO2 carbon stable isotope analyses at the microscale using Raman spectroscopy

Measuring the carbon stable isotope ratio (13C/12C, expressed as δ13CCO2) in geogenic CO2 fluids is a crucial geochemical tool for studying Earth's degassing. Carbon stable isotope analysis is traditionally performed by bulk mass spectrometry. Although Raman spectroscopy distinguishes 12CO2 and 13CO2 isotopologue bands in spectra, using this technique to determine CO2 isotopic signature has been challenging. Here, we report on in-situ non-destructive analyses of the C stable isotopic composition of CO2, applying a novel high-resolution Raman configuration on 42 high-density CO2 fluid inclusions in mantle rocks from the Lake Tana region (Ethiopia) and El Hierro (Canary Islands). We collected two sets of three spectra with different acquisition times at high spectral resolution in each fluid inclusion. Among the 84 sets of spectra, 58 were characterised by integrated 13CO2/12CO2 band area ratios with reproducibility better than 4‰. Our results demonstrate the determination of δ13CCO2 by Raman spectroscopy in individual fluid inclusions with an error better than 2.5 ‰, which satisfactorily matches bulk mass spectrometry analyses in the same rock samples, supporting the accuracy of the measurements. We thus show that Raman Spectroscopy can provide a fundamental methodology for non-destructive, site-specific, and spatially resolved carbon isotope labelling at the microscale.

Supercritical Carbon Dioxide Shock Behavior Near the Critical Point

Abstract This paper aims to provide an understanding of sCO2 inviscid adiabatic normal shock behavior near the critical point and to develop an explicit tool for faster prediction of the shock relations that can aid the supercritical turbomachinery design process. An iterative algorithm was developed to compute shockwave behaviors for nonideal fluids. Three important shock behavior parameters were investigated: postshock Mach number, shock strength, and polytropic efficiency. A comparative study was carried out between air (ideal gas assumption), ideal gas CO2 (ideal gas assumption), and nonideal fluid CO2 (Span–Wagner equation of state). The distinct differences show the inadequacy of the perfect gas shock relations when predicting sCO2 shock behavior near the critical point. The results of nonideal fluid calculations show a general trend of stronger shock strengths and higher polytropic efficiencies toward lower preshock entropy conditions. This is also distinctive near the critical point due to the reduced speed of sound. Finally, explicit expressions for these parameters were retrieved using symbolic regression. The fitted models have significant improvements compared to the prediction from perfect gas shock relations with a 5–20% point reduction in relative errors. This study also shows the potential for machine learning to be applied in nonideal fluid effects modeling and the methodology developed in this paper can be easily introduced to other working fluids in their ranges of interest.

Pore-Scale Characterization of CO2 Trapping and Oil Displacement in Three-Phase Flow in a Heterogeneous Layered Sandstone

Summary Permeability variation in the vertical direction, a typical sandstone reservoir heterogeneity, can trap a large amount of oil in the low-permeability layer. We performed water-alternating-gas (WAG) injection and CO2 foam flooding on a specially constructed millimeter-sized layered sandstone and investigated fluid distribution using high-resolution X-ray microtomography. Based on the segmented images, CO2 capillary-trapping capacity, oil recovery, Euler number, shaper factor, capillary pressure, and fluid flow conductivity were calculated. Our results show that increasing the number of WAG cycles favored CO2 capillary trapping, and oil recovery was enhanced by the WAG strategy. However, there was still a significant amount of oil trapped in the low-permeability layer. After the WAG injection, the connectivity of the residual oil clusters decreased, the capillary pressure of the oil clusters increased, and oil flow conductivity decreased. This was not conducive to further oil recovery. The subsequent injection of CO2 foam effectively recovered the oil in the low-permeability layer. During the no-injection period, we observed a crossflow phenomenon caused by gravity segregation (the high-permeability layer was located below the low-permeability layer), i.e., oil in the low-permeability layer decreased while oil in the high-permeability layer increased, which is beneficial for subsequent oil production. Furthermore, CO2 moved upward driven by gravity, and although capillary barriers could prevent CO2 from escaping, subsequent water injection was essential to improve the stability of CO2 capillary trapping. This work accurately quantifies the distribution of oil and gas in high- and low-permeability layers, thus providing fundamental data for oil recovery and CO2 trapping in reservoirs with vertical heterogeneity. Although the sample used in the experiment was not natural reservoir rock, our results imply that when the permeability ratio between the two layers is greater than 2, sufficient attention must be paid to the fluid distribution differences caused by this layered heterogeneity. Different displacement strategies, such as WAG and CO2 foam flooding, or gravity differences between oil and gas can be used to enhance oil recovery.

One-dimensional sepiolite confined ionic liquids structure to improve the electrochemical performance of polyethylene-oxide based composite polymer electrolyte

Polyethylene-oxide (PEO) based composite polymer electrolytes (CPEs) with one-dimensional sepiolite confined ionic liquids (ILs) structure is constructed to further improve Li+ conductivity and reduce cost. Silicon nanorods (SNRs) is obtained by microwave-assisted acid activation of sepiolite and then ILs is confined into SNRs by supercritical CO2 fluid. The specific surface area of SNRs reduces from 170.88 m2 g-1 to 2.19 m2 g-1 after ILs confining, and the morphology and component of ILs in SNRs channel are clearly detected, indicating that the SNRs confined ILs structure (ILs@SNRs) is successfully obtained. The Li+ conductivity of CPEs increases from 1.40 × 10-6 S cm-1 to 0.922 × 10-4 S cm-1, which indicates that ILs confined in SNRs provide a fast channel for Li+ transmission. Besides, the reduction of PEO crystallinity is also favorable to Li+ transmission. The corresponding lithium symmetrical battery and LiFePO4 battery has excellent electrochemical performances. The good rate performance is attributed to the high Li+ migration number of 0.261 compare to 0.122 of PEO. Compared with the simple mixing of polymer and ILs, the confined ILs in SNRs channel will not be lost, which maintains the stability of Li+ transmission and reduces the consumption amount of ILs thus greatly reducing the cost of CPEs.

Comparative study on different extraction methods of oil extract from Mentha asiatica Boriss. and optimization of the extraction process by response surface methodology

AbstractIn the current study, the lipophilic solvent (n‐hexane) extraction, steam distillation (SD) and supercritical CO2 fluid extraction (SC–CO2) methods were used to extract the volatile components of Mentha asiatica Boriss. Comparisons were made between the extraction yield, chemical component and biological activity. Gas chromatography quadrupole‐time‐of‐flight mass spectrometry (GC–QTOF–MS) and semi‐quantitative analysis of chemical contents by flame ionization detector (GC–FID) were used to study the chemical ingredients in Mentha asiatica Boriss. aromatic extract. The oil extract obtained from lipophilic solvent (n‐hexane) extraction (1.27 ± 0.03%, w/W) showed the highest yield, followed by supercritical CO2 fluid extraction (1.15 ± 0.04%, w/W), the extraction rate of SD was (0.37 ± 0.01%，w/W). The oil extract of Mentha asiatica Boriss. contained a total of 70 components that were identified. In the following, the primary volatile compounds of the essential oil produced using the three extraction techniques: α‐thujene, camphene, sabinene, β‐pinene, β‐cymene, limonene, β‐terpinene, camphol, α‐terpinene, carvenone, carvone, piperitone oxide, thymol, myrtenyl acetate, dihydrojasmone, caryophyllene, germacrene D and caryophyllene oxide. Findings from this study indicate that the three methods of essential oil extraction produced oils with varying antioxidant capacities against DPPH and ABTS free radicals. Against Staphylococcus aureus, Candida albicans, Bacillus subtilis and Escherichia coli, all of the essential oils simultaneously showed clear inhibitory actions. Response surface methodology (RSM) and the Box–Benhnken design with three factors and three levels were both utilized to optimize the distillation process of essential oils. The appropriate extraction parameters were a 3 h extraction period, a solid–liquid ratio of 1:10 and a 3 h soaking time. The highest yield of essential oil was 0.38%. The impact of extraction parameters on essential oil yield was examined using the SD method. The findings indicated that the main factors affecting the yield of volatile oil extracted by SD were soaking time > ratio of solid to liquid > extraction time.

The impacts of CO2 flooding on crude oil stability and recovery performance

Numerous studies have investigated the fundamental mechanisms by which CO2 flooding can increase oil production by altering the properties of the hydrocarbon fluid, including oil swelling, viscosity and interfacial tension reductions, and the extraction of light-to-intermediate components. However, the interactions between CO2 and hydrocarbon fluid may also cause several problems, such as asphaltene precipitation due to crude oil's instability during the CO2 flooding process. This study investigates the complex factors that affect the instability of crude oil, including CO2 injection pressures, temperatures, and crude oil compositions. The light-dead oil samples taken from two Indonesian oil fields were used. The impacts of the instability of crude oil on CO2 displacement performance were also observed to evaluate oil recovery and minimum miscibility pressure (MMP). The observation was performed using a slim tube under varying CO2 high-pressure injections at 90 °C and 70 °C. The produced oils were analyzed based on their polarity component, saturates, aromatics, resins, and asphaltenes fractions, to observe the changes in oil composition and colloidal index instability. The results showed that increasing temperatures at given pressures resulted in higher oil recovery. Moreover, the asphaltene and resin fractions in the oil produced at a lower temperature significantly decrease compared to those at a higher temperature. It was also shown that asphaltene tends to precipitate more easily at a lower temperature. The other phenomenon revealed that the lighter oil resulted in a lower recovery than the heavier oil at a given pressure and temperature and correspondingly higher MMP. It was also suggested that CO2 flooding is more likely to cause asphaltene precipitation in light oils.

Orogenic lode-gold deposits and listvenization processes in the El-Barramiya area, Eastern Desert, Egypt

Gold mineralization in the El-Barramiya region of the Eastern Desert, Egypt, is connected to the post-accretionary stage throughout the Central Eastern Desert. It is represented by quartz, quartz-carbonate veins and disseminations in listvenite rocks. The thrust contact between rock units in El-Barramiya area played an imperative part in gold mineralization where the obduction of ophiolitic rocks over the metasediments and metavolcanics caused shear zones. Mineralization in the study area formed along shear zones and the gold mineralization prefers to precipitate along the transition zone between low-grade regional metamorphic area which is represented by metasediments and high grade which is represented by actinolite schist. The gold mineralization lode of El-Barramiya gold mine area is situated in E–W trending quartz and quartz-carbonate veins along a shear zone located in the intersections between faults trend in NE–SW (Najd fault), NW–SE and thrust faults trend in NEE–SWW in metavolcanic and metasedimentary host rocks. Porphyry granite in the mine area played an important role in hydrothermal alteration process where it represents the source of K, listvenite formed when fluids rich in CO2 and bearing-K permeate and alter the previously altered ultramafic rocks, usually serpentinites of the ophiolitic mélange rocks. The listvenitization process includes silicification and carbonatization metasomatic processes, tectonized serpentinites are altered to listvenite as the carbonatization becomes more intense close to dipping transpressive faults. Geochemical studies of listvenite and mineralized veins helped to determine the ultramafic genesis of listvenite and gold transformed as gold bisulfide. The whole rock geochemical data from El-Barramiya and elsewhere indicate that the transformation of serpentinite into listvenite involves profound metasomatic modification of the bulk-rock geochemistry. The chemical changes during alteration of serpentinite to listvenite are dominated by the addition of CO2, the removal of H2O, and the redistribution of SiO2, MgO and CaO as carbonate minerals and silica replace serpentine. All listvenites at El-Barramiya lode gold deposit are enriched in CaO, Fe2O3 and K2O, but depleted in MgO compared with associated serpentinite that is presumed to represent their protoliths. The chemical changes during alteration of serpentinite to listvenite are dominated by the addition of CO2, the removal of H2O, and the redistribution of SiO2, MgO and CaO as carbonate minerals and silica replace serpentine. Alteration also caused redistribution of trace elements, with some being locally remobilized within the rock, some being added from a fluid phase, and others being leached out of the rock. Petrographic investigation and geochemical studies show different types of alterations (carbonatization and silicification) and mineralization. Mineralizations are represented by gold and sulfides (pyrite, arsenopyrite and smaller quantities of chalcopyrite, sphalerite, galena, tetrahedrite and gersdorffite) found in auriferous quartz veins and disseminated in listvenite. The area exposed to brittle–ductile deformation in addition to different types of structures such as faults and fractures controlling on the formation of mineralization and act as hydrothermal channels ways for fluid flow. Fluid inclusions studies revealed that gold mineralization was formed from heterogeneous trapping of H2O–CO2 fluids at a temperature of 280–340 °C and pressure within the range of 1.5–1.9 kbar, which is consistent with the mesothermal conditions.

Active Ingredients of Schisandra chinensis Fruit Oil and their Effect on Propionibacterium acnes-Induced Inflammation in HaCaT Cells.

Propionibacterium acnes causes upregulation of inflammatory factors, such as cycloxygenase-2, prostaglandin E2, interleukin-1β, and tumor necrosis factor-alpha, increased levels of reactive oxygen species (ROS) and inward flow of calcium ions. This causes increased levels of the antimicrobial peptide LL-37 and inflammation of the skin, leading to redness, swelling, itching and other symptoms. Schisandra chinensis fruit oil (SCO) is rich in lignan active ingredients with various antioxidant and anti-inflammatory properties. In this study, SCO is obtained by supercritical CO2 fluid extraction. SCO's anti-inflammatory actions were investigated using P. acnes-induced inflammation HaCaT cells model. A method based on reversed-phase high-pressure liquid chromatography with a diode array detector was developed and validated for the simultaneous detection of five lignan components. Levels of inflammatory factors and LL-37 were measured by ELISA kit and western blot respectively. Ca2+ and ROS levels detected by flow cytometry. The experimental results show that the contents of schisanol A, schisanol B, schisanin A, schisanin B, and schisanin C were 33.89 ± 0.24, 14.89 ± 0.45, 8.92 ± 0.02, 29.14 ± 0.67, and 4.74 ± 0.09 mg/g, respectively. Studies have demonstrated that SCO can alleviate skin inflammation by inhibiting the COX-2/PGE2 and NF-κB signalling pathway. In addition, SCO can inhibit ROS production, significantly block inward Ca2+ flow, alleviate cell damage, and modulate the content of the antimicrobial peptide LL-37. In summary, our study elucidated the anti-inflammatory activity of SCO in a cell model and provided a scientific basis for its application as a raw material in skin care.

Research on non-equilibrium condensation of supercritical carbon dioxide in sCO2 power systems

Based on the consideration of sustainable development and energy efficient transformation, people propose using renewable energy to upgrade traditional power generation systems. The supercritical carbon dioxide (sCO2) Brayton cycle has a great utilization potentiality in thermodynamic systems, such as solar thermal power generation systems. When the CO2 fluid flows into the compressors of sCO2 power systems, there is a risk of non-equilibrium condensation due to local expansion and acceleration, which seriously threatens the stability of the whole system. The convergent-divergent nozzle is usually used to study non-equilibrium condensation. In this paper, the wet steam model is used to simulate the non-equilibrium condensation of the CO2 fluid near its critical region in a convergent-divergent nozzle. The phase change model and the thermophysical equation of state are verified by experimental data. The non-equilibrium condensation process is analyzed, and the droplet nucleation process and droplet growth process are described. Non-equilibrium condensation releases the latent heat and forms a condensation shock wave. The influences of the shock wave effect on temperature, pressure, and other parameters are discussed. The initial condensation position and critical subcooled temperature under different inlet conditions are analyzed.

Diamond Formation via Carbonate or CO2 Reduction under Pressures and Temperatures of the Lithospheric Mantle: Review of Experimental Data

Existing ideas about the polygenic origin of diamonds in nature involve various processes, mechanisms, and driving forces for diamond crystallization, including redox reactions, changes in P-T conditions, evolution of melt or fluid composition, and others. According to classical models, in the lithospheric mantle, diamond formation occurs at depths of 120–210 km and temperatures of 900–1500 °C as a result of metasomatic processes. The driving forces in these models are considered to be redox reactions leading to the reduction of carbonates, carbonate melts, or CO2 to elemental carbon. In this study, we provide a review and systematization, as well as experimental issues and possible future directions of experimental studies, on diamond crystallization from carbonate carbon through redox reactions at P,T (pressure, temperature) conditions relevant to the lithospheric mantle. These studies have demonstrated that silicon, metals (FeSi, Fe, Fe-Nialloys), carbides (SiC, Fe3C, Fe7C3), reduced components of C-O-H fluid, sulfides/sulfide melts, Fe-S-C melts, and the application of an electric field (potential difference) can act as reducing agents for carbonate/carbonate-bearing melts or CO2 fluid, leading to the formation of diamond and graphite. The experimental data reviewed in this paper not only indicate the fundamental possibility of diamond formation from carbonate carbon through the reduction of carbonate, carbonate-bearing phases, or CO2 in the mantle, but also reveal the characteristic features of the resulting diamonds. Furthermore, the significance of potential reducing agents (fluid, sulfide, silicon, metal, and carbide) in various geodynamic settings, including the lithospheric mantle at depths insufficient for stabilizing iron or carbides, has been identified.

Field pilot testing and reservoir simulation to evaluate processes controlling CO2 injection and associated in-situ fluid migration in deep coal

A key strategy for reducing global CO2 emissions is geologic sequestration of CO2. Deep, unmineable coal seams have been proposed as possible targets for CO2 injection and storage because of the global distribution of coal resources, and relative security of CO2 storage associated with CO2 adsorption. However, the current paradigm is that near-injector permeability loss caused by pure CO2 adsorption-induced coal swelling limits the effectiveness of this process making coal a less than an ideal target for CO2 injection/sequestration.In order to test the viability of CO2 injection and storage in deep coal seams, and evaluate processes controlling CO2 injection, migration and storage therein, a field pilot was implemented in the Mannville Coal (∼1500 m depth) of Alberta, Canada. An additional objective of the field pilot was to quantify the migration of water and natural gas away from the CO2 injection well, an important mechanism used to improve the performance of the pilot operator's enhanced hydrogen recovery (EHR™) process. To achieve these multiple objectives, a vertical injection well and closely-spaced offsetting vertical observation well were drilled, cored, and completed in the Mannville coal seams, and instrumented with pressure sensors to monitor both the coal and bounding zones during injection testing. Periodic fluid sampling at the observation well allowed for quantification of CO2 plume and fluid migration. Pre-CO2 injection/falloff testing was performed with water at variable injection rates/pressures to assess coal permeability/porosity changes without the complication of CO2-coal interaction. CO2 injection/falloff tests were then performed at increasing CO2 injection rates to assess the combined impact of injection pressure/CO2 rate and CO2-coal interaction (e.g., adsorption) on injectivity. All tests were history-matched with a numerical reservoir simulator; the calibrated model was used to study the key controls on CO2 storage, CO2 plume migration, in-situ fluid displacement, and injectivity.A key finding from simulation of the pilot results is that, for the Mannville coals in the study area, permeability increases caused by coal natural fracture dilation during injection outweigh permeability decreases caused by CO2 adsorption-induced coal swelling, resulting in an injectivity index increase with CO2 injection rate. In addition, the coals exhibit strong anisotropy in permeability and geomechanical properties; ignoring coal anisotropy in the simulation model causes coal swelling effects to be overestimated, resulting in an underestimate in CO2 plume extent.From the pilot results and analysis, it can be concluded that the deep Mannville coal could be a viable target for CO2 storage.

Mechanism for the Formation of Nanoscale Oxides in a Medium of Supercritical CO2 Fluid

A possible mechanism is considered for the formation of nanoscale oxides based on titanium and aluminum isopropoxides in a medium of supercritical CO2 fluid. It is shown that because of intermolecular interactions and high pressure in the system, the supercritical fluid acquires the properties of a condensed medium, the main role of which is to restrain processes of hydrolysis. At the first stage of the hydrolysis of titanium isopropoxide, the water molecule is coordinated in the outer sphere of the central atom due to the formation of intermolecular hydrogen bonds. It is then coordinated into the inner sphere with the formation of a five-coordinate transition state and its destruction, creating a product substituted for the hydroxo group. The next steps proceed in a similar way. The described mechanism agrees with experimental findings and produces nanosized X-ray amorphous titanium oxide. (With aluminum isopropoxide, only the hydrolyzed hydroxo form can be produced.) Results suggest the production of nanosized oxides from isopropoxides in a medium of supercritical CO2 fluid is possible for transitional d-elements.

Mechanism for the Formation of Nanoscale Oxides in a Medium of Supercritical CO2 Fluid

Mechanism for the Formation of Nanoscale Oxides in a Medium of Supercritical CO2 Fluid

Effects of H2O–CO2 Fluids, Temperature, and Peridotite Fertility on Partial Melting in Mantle Wedges and Generation of Primary Arc Basalts

Abstract Many lines of evidence from high P–T experiments, thermodynamic models, and natural observations suggest that slab-derived aqueous fluids, which flux mantle wedges contain variable amounts of dissolved carbon. However, constraints on the effects of H2O–CO2 fluids on mantle melting, particularly at mantle wedge P–T conditions, are limited. Here, we present new piston cylinder experiments on fertile and depleted peridotite compositions with 3.5 wt.% H2O and XCO2 [= molar CO2 / (CO2 + H2O)] of 0.04–0.17. Experiments were performed at 2–3 GPa and 1350°C to assess how temperature, peridotite fertility, and XCO2 of slab-derived fluid affects partial melting in mantle wedges. All experiments produce olivine + orthopyroxene +7 to 41 wt.% partial melt. Our new data, along with previous lower temperature data, show that as mantle wedge temperature increases, primary melts become richer in SiO2, FeO*, and MgO and poorer CaO, Al2O3, and alkalis when influenced by H2O–CO2 fluids. At constant P–T and bulk H2O content, the extent of melting in the mantle wedge is largely controlled by peridotite fertility and XCO2 of slab-fluid. High XCO2 depleted compositions generate ~7 wt.% melt, whereas, at identical P–T, low XCO2 fertile compositions generate ~30 to 40 wt.% melt. Additionally, peridotite fertility and XCO2 have significant effects on peridotite partial melt compositions. At a constant P–T–XCO2, fertile peridotites generate melts richer in CaO and Al2O3 and poorer in SiO2, MgO + FeO, and alkalis. Similar to previous experimental studies, at a constant P–T fertility condition, as XCO2 increases, SiO2 and CaO of melts systematically decrease and increase, respectively. Such distinctive effects of oxidized form of dissolved carbon on peridotite partial melt compositions are not observed if the carbon-bearing fluid is reduced, such as CH4-bearing. Considering the large effect of XCO2 on melt SiO2 and CaO concentrations and the relatively oxidized nature of arc magmas, we compare the SiO2/CaO of our experimental melts and melts from previous peridotite + H2O ± CO2 studies to the SiO2/CaO systematics of primitive arc basalts and ultra-calcic, silica-undersaturated arc melt inclusions. From this comparison, we demonstrate that across most P–T–fertility conditions predicted for mantle wedges, partial melts from bulk compositions with XCO2 ≥ 0.11 have lower SiO2/CaO than all primitive arc melts found globally, even when correcting for olivine fractionation, whereas partial melts from bulk compositions with XCO2 = 0.04 overlap the lower end of the SiO2/CaO field defined by natural data. These results suggest that the upper XCO2 limit of slab-fluids influencing primary arc magma formation is 0.04 < XCO2 < 0.11, and this upper limit is likely to apply globally. Lastly, we show that the anomalous SiO2/CaO and CaO/Al2O3 signatures observed in ultra-calcic arc melt inclusions can be reproduced by partial melting of either CO2-bearing hydrous fertile and depleted peridotites with 0 < XCO2 < 0.11 at 2–3 GPa, or from nominally CO2-free hydrous fertile peridotites at P > 3 GPa.

Experimental Modeling of Decarbonation Reactions, Resulting in the Formation of CO2 Fluid and Garnets of Model Carbonated Eclogites under Lithospheric Mantle P,T-Parameters

First experimental modeling of decarbonation reactions resulting in the formation of CO2-fluid and Mg, Fe, Ca, and Mn garnets, with composition corresponding to the garnets of carbonated eclogites of types I and II (ECI and ECII), was carried out at a wide range of lithospheric mantle pressures and temperatures. Experimental studies were performed on a multi-anvil high-pressure apparatus of a “split sphere” type (BARS), in (Mg, Fe, Ca, Mn)CO3-Al2O3-SiO2 systems (with compositional variations according to those in ECI and ECII), in the pressure interval of 3.0–7.5 GPa and temperatures of 1050–1450 °C (t = 10–60 h). A specially designed high-pressure cell with a hematite buffering container—preventing the diffusion of hydrogen into the platinum capsule—was used, in order to control the fluid composition. Using the mass spectrometry method, it was proven that in all experiments, the fluid composition was pure CO2. The resulting ECI garnet compositions were Prp48Alm35Grs15Sps02–Prp44Alm40Grs14Sps02, and compositions of the ECII garnet were Prp57Alm34Grs08Sps01–Prp68Alm23Grs08Sps01. We established that the composition of the synthesized garnets corresponds strongly to natural garnets of carbonated eclogites of types I and II, as well as to garnets from xenoliths of diamondiferous eclogites from the Robert Victor kimberlite pipe; according to the Raman characteristics, the best match was found with garnets from inclusions in diamonds of eclogitic paragenesis. In this study, we demonstrated that the lower temperature boundary of the stability of natural garnets from carbonated eclogites in the presence of a CO2 fluid is 1000 (±20) °C at depths of ~90 km, 1150–1250 (±20) °C at 190 km, and 1400 (±20) °C at depths of about 225 km. The results make a significant contribution to the reconstruction of the fluid regime and processes of CO2/carbonate-related mantle metasomatism in the lithospheric mantle.