Littérature scientifique sur le sujet « Δ13CCO2 »

AbstractGeochemical and isotopic monitoring of coalbed gases at the excavation fields of mining areas in Velenje Coal Basin, Slovenia, has been ongoing since the year 2000 with the aim of obtaining better insights into the distribution and origin of coalbed gases. Results from the mining areas Pesje and Preloge (active excavation fields) are presented here from the year 2000 up to the present. Composition and origin of coalbed gases were determined using mass spectrometry at the Jožef Stefan Institute. From a larger database of geochemical samples, 119 samples were used for analysis and spatial presentation in a geographical information system (GIS) environment. We have used geochemical (CH4, CO2 and N2) and isotopic (δ13CCO2 and δ13CCH4) tracers for geochemical and isotopic characterisation of coalbed gases from the active excavation fields. Concentrations of CO2 and the carbon dioxide–methane indices in the southern part of the basin are higher than in the northern part of the basin due to the vicinity of the active Šoštanj Fault. The value of δ13CCH4 at the active excavation field indicates a bacterial origin, with values greater than –50‰, and only some boreholes show elevated δ13CCH4 quantities as a consequence of the CO2 reduction process in Velenje Coal Basin. The value of δ13CCO2 indicates the bacterial and endogenic origin of carbon.

In this study, two shale samples with different maturities, from Geniai, Lithuania (Ro = 0.7%), and Wenjiaba, China (Ro = 2.7%), were selected for open-system pyrolysis experiments at 400 °C and 500 °C, respectively. The generation of isotopic gases from the shales with different maturities was investigated, and the effects of pyrite catalysis on the carbon isotopic compositions were also studied. It was found that CO2, CH4 and their isotopic gases were the main gaseous products of the pyrolysis of both shales, and more hydrocarbon gases were generated from the low-maturity Geniai shale. The δ13C1 values fluctuated from −40‰ to −38‰, and δ13C2 showed higher values (−38‰~−34‰) for the Geniai shale. In addition, its δ13CCO2 values ranged from −28‰ to −26‰. Compared with the Geniai shale, lower δ13C1 values (−43‰~−42‰) and higher δ13CCO2 values (−19‰~−14‰) were detected for the Wenjiaba shale. As temperature increased, CH4 became isotopically lighter and C2H6 became isotopically heavier, which changes were due to the mass-induced different reaction rates of 12C and 13C radicals. Furthermore, the pyrite made the kinetic isotope effect stronger and thus made the CH4 isotopically lighter for both shales, especially at the lower temperature of 400 °C.

The article presents modern data on the chemical, gas composition, the content of the stable isotopes of oxygen, hydrogen, carbon and sulfur in the natural mineral waters of the Essentuki field. A detailed study of the geological and hydrogeological features of the water circulation territory, their macro components composition, the content of organic matter in the water, temperature conditions and values of δ18ОSMOW, δDSMOW, δ13СDIC, δ18ОDIC, δ34SVCDT, δ13CCO2, δ13CCH4, δ15N revealed the genesis of the aqueous, gas and salt components of the natural mineral waters of the Essentuki field. Established that all natural mineral waters of the Essentuki field are meteoric infiltration waters. The heterogeneous component composition of the natural mineral waters, that circulate in various aquifers, represents the features of the lithological composition of the water-bearing rocks, the degree of openness or closeness of faults and the intensity of reactions in the water-rock-gas-organic matter system.

Fluids responsible for regional 18O-depletion of Neoproterozoic igneous rocks in Avalonia are investigated here through a petrographic, microthermometric, and stable isotopic examination of fluid inclusions and minerals from the abundant vein networks of the Mira terrane, Cape Breton Island. Six categories of vein assemblages — from oldest to youngest — are present: (i) quartz–albite, (ii) quartz–epidote, (iii) quartz, (iv) quartz–chlorite–calcite, (v) quartz–calcite, and (vi) calcite. Vein system temperatures were initially as high as ∼300 °C and gradually decreased to ∼200 °C. Moderate salinities (<8 equivalent wt.% NaCl) characterize entrapped fluids in the early quartz–albite veins but decrease in later quartz–epidote and quartz–calcite veins to <1 equiv. wt.% NaCl. The limited range of fluid δ18O values (–1.9‰ to +1.4‰) calculated for most of the vein assemblages is suggestive of a seawater-dominated system, as are the δDH2O values (–12‰ to –3‰) obtained for epidote. Decreasing fluid salinities, however, suggest that meteoric water became dominant during later stages of vein formation. The carbon isotopic compositions of trace CO2 and CH4 from the fluid inclusions (δ13CCO2 = –22‰ to –4‰; δ13CCH4 = –52‰ to –37‰) are indicative of externally derived (i.e., non-magmatic) fluids of organic origin.

This article presents the new data on the chemical and gas composition, the content of stable isotopes of oxygen, hydrogen, carbon, and sulfur in natural mineral waters of the Essentuki field. A detailed study of the geological and hydrogeological features of the water circulation area, its major chemical composition, the content of organic matter in water, temperature conditions and δ18OSMOW, δDSMOW, δ13CDIC, δ18ODIC, δ34SVCDT, δ13CCO2, δ13CCH4, δ15N values made it possible to specify the genesis of water, gas, and solute components of the Essentuki CO2-rich mineral water field. The stable isotopes values (δ18OSMOW and δDSMOW) in the water phase ranges from −13.75 to −9.69‰ and from −101.08 to −74.34‰, respectively. They correspond to GMWL, which indicates their predominantly infiltration genesis. The values of δ13CDIC in mineral waters of the Essentuki field vary widely from −14.43 to +8.59‰ and indicate their mixed genesis. δ15N gas values in mineral waters of the Essentuki field vary quite widely from −2.31 to 2.50‰ indicating a different source of this gas. Obtained data prove that all mineral waters in the Essentuki field are infiltration waters, and the heterogeneous component composition of waters circulating in different aquifers reflects the lithological composition of water-bearing strata, the rate of openness/closure of faults and the intensity of reactions in the «water-rock-gas-organic matter» system.

In this work, Huadian oil shale was extracted by subcritical water at 365 °C with a time series (2–100 h) to better investigate the carbon isotope fractionation characteristics and how to use its fractionation characteristics to constrain the oil recovery stage during oil shale in situ exploitation. The results revealed that the maximum generation of oil is 70–100 h, and the secondary cracking is limited. The carbon isotopes of the hydrocarbon gases show a normal sequence, with no “rollover” and “reversals” phenomena, and the existence of alkene gases and the CH4-CO2-CO diagram implied that neither chemical nor carbon isotopes achieve equilibrium in the C-H-O system. The carbon isotope (C1–C3) fractionation before oil generation is mainly related to kinetics of organic matter decomposition, and the thermodynamic equilibrium process is limited; when entering the oil generation area, the effect of the carbon isotope thermodynamic equilibrium process (CH4 + 2H2O ⇄ CO2 + 4H2) becomes more important than kinetics, and when it exceeds the maximum oil generation stage, the carbon isotope kinetics process becomes more important again. The δ13CCO2−CH4 is the result of the competition between kinetics and thermodynamic fractionation during the oil shale pyrolysis process. After oil begins to generate, δ13CCO2−CH4 goes from increasing to decreasing (first “turning”); in contrast, when exceeding the maximum oil generation area, it goes from decreasing to increasing (second “turning”). Thus, the second “turning” point can be used to indicate the maximum oil generation area, and it also can be used to help determine when to stop the heating process during oil shale exploitation and lower the production costs.

The hydrothermal caves linked to active faulting can potentially harbour subterranean atmospheres with a distinctive gaseous composition with deep endogenous gases, such as carbon dioxide (CO2) and methane (CH4). In this study, we provide insight into the sourcing, mixing, and biogeochemical processes involved in the dynamic of deep endogenous gas formation in an exceptionally dynamic hypogenic karst system (Vapour Cave, southern Spain) associated with active faulting. The cave environment is characterized by a prevailing combination of rising warm air with large CO2 outgassing (>1%) and highly diluted CH4 with an endogenous origin. The δ13CCO2 data, which ranges from −4.5 to −7.5‰, point to a mantle-rooted CO2 that is likely generated by the thermal decarbonation of underlying marine carbonates, combined with degassing from CO2-rich groundwater. A pooled analysis of δ13CCO2 data from exterior, cave, and soil indicates that the upwelling of geogenic CO2 has a clear influence on soil air, which further suggests a potential for the release of CO2 along fractured carbonates. CH4 molar fractions and their δD and δ13C values (ranging from −77 to −48‰ and from −52 to −30‰, respectively) suggest that the methane reaching Vapour Cave is the remnant of a larger source of CH4, which was likely generated by microbial reduction of carbonates. This CH4 has been affected by a postgenetic microbial oxidation, such that the gas samples have changed in both molecular and isotopic composition after formation and during migration through the cave environment. Yet, in the deepest cave locations (i.e., 30 m below the surface), measured concentration values of deep endogenous CH4 are higher than in atmospheric with lighter δ13C values with respect to those found in the local atmosphere, which indicates that Vapour Cave may occasionally act as a net source of CH4 to the open atmosphere.

Methane microseepage is the result of natural gas migration from subsurface hydrocarbon accumulations to the Earth’s surface, and it is quite common in hydrocarbon-prone basins. In this study, by analyzing gas concentrations and isotope composition of soil gas, the potentials of CH4 gas transferred to the surface were studied at three measurement transects in Dawanqi oilfield, Tarim Basin, China. It was found that CH4 from deep-buried reservoirs could migrate upwards to the surface through faults, fissures, and permeable rocks, during which some CH4 was oxidized and the unoxidized methane remained in the soil or was emitted into the atmosphere. Soil gas samples had mean concentrations of 907.1, 62.3, 21.7, 11.0, and 5.8 ppmv for CH4, C2H6, C3H8, C4H10, and C5H12, respectively. The C1/C2+ (13.3 for soil gas and 3.75 for absorbed gas) and gas wetness ratio (12% for soil gas and 26% for absorbed gas) suggested that the hydrocarbons were derived from a thermogenic process. According to isotope composition analysis, the δ13CCO2, δ13CCH4, and δDCH4 values for the soil gas from Dawanqi oilfield varied from -15.5 to -17.2‰, -11‰ to -17‰, and -150 to -189‰, respectively. The extreme 13C enrichment in CH4 is possibly because of the fractionation effects of diffusional migration and methanotrophic oxidation. Soil gas and absorbed gas showed high CH4 concentrations at the edge of the fault block, which indicated that fault was conductive to gas migration. Also, gas migrated from the surface to the atmosphere in the center region of the fault block because of the high permeability and shallow depth of the reservoir in Dawanqi oilfield.

Abstract. The reason for the initial rise in atmospheric CO2 during the last deglaciation remains unknown. Most recent hypotheses invoke Southern Hemisphere processes such as shifts in midlatitude westerly winds. Coeval changes in the Atlantic meridional overturning circulation (AMOC) are poorly quantified, and their relation to the CO2 increase is not understood. Here we compare simulations from a global, coupled climate–biogeochemistry model that includes a detailed representation of stable carbon isotopes (δ13C) with a synthesis of high-resolution δ13C reconstructions from deep-sea sediments and ice core data. In response to a prolonged AMOC shutdown initialized from a preindustrial state, modeled δ13C of dissolved inorganic carbon (δ13CDIC) decreases in most of the surface ocean and the subsurface Atlantic, with largest amplitudes (more than 1.5‰) in the intermediate-depth North Atlantic. It increases in the intermediate and abyssal South Atlantic, as well as in the subsurface Southern, Indian, and Pacific oceans. The modeled pattern is similar and highly correlated with the available foraminiferal δ13C reconstructions spanning from the late Last Glacial Maximum (LGM, ~19.5–18.5 ka BP) to the late Heinrich stadial event 1 (HS1, ~16.5–15.5 ka BP), but the model overestimates δ13CDIC reductions in the North Atlantic. Possible reasons for the model–sediment-data differences are discussed. Changes in remineralized δ13CDIC dominate the total δ13CDIC variations in the model but preformed contributions are not negligible. Simulated changes in atmospheric CO2 and its isotopic composition (δ13CCO2) agree well with ice core data. Modeled effects of AMOC-induced wind changes on the carbon and isotope cycles are small, suggesting that Southern Hemisphere westerly wind effects may have been less important for the global carbon cycle response during HS1 than previously thought. Our results indicate that during the early deglaciation the AMOC decreased for several thousand years. We propose that the observed early deglacial rise in atmospheric CO2 and the decrease in δ13CCO2 may have been dominated by an AMOC-induced decline of the ocean's biologically sequestered carbon storage.

Questa tesi indaga l'applicabilità della micro-spettroscopia Raman per migliorare la caratterizzazione dei fluidi a CO2 terrestri, intrappolati come inclusioni fluide (FI) nelle peridotiti. Nello spettro Raman della CO2, la distanza delle due vibrazioni fondamentali è densità (d) dipendente, inoltre sono visibili le vibrazioni 13CO2 e 12CO2. Ciò permette alla micro-spettroscopia Raman di avere il potenziale per caratterizzare in situ FI a CO2, consentendo di comprendere meglio i meccanismi di trasporto del C all'interno della Terra. La proporzionalità tra le aree 13CO2 e 12CO2 con la loro concentrazione molare permette di calcolare il δ13CCO2 tramite micro-spettroscopia Raman. I rapporti delle aree richiedono precisione sulla 4° decimale per dare valori di δ13CCO2 rappresentativi dei serbatoi naturali terrestri. Gli spettri Raman sono influenzati da inevitabili effetti casuali che riducono la precisione dell'area. 42 FI a CO2 pura di alta d, provenienti dalla regione del Lago Tana e da El Hierro, sono state analizzate. Per ogni FI sono state acquisite due serie di spettri con tempi di acquisizione diversi. Di 84 serie di analisi, 23 avevano rapporti di area 13CO2/12CO2 diversi tra loro di più di un ordine di grandezza. Questi sono stati rimossi dal dataset. Il 95% dei restanti 61 set aveva riproducibilità dei rapporti di area <≈4‰, consentendo di calcolare valori di δ13CCO2 con precisione <±≈2‰. Solo poche analisi erano caratterizzate da una minore precisione. I valori di δ13CCO2 calcolati per FI nelle peridotiti dalla regione del Lago Tana hanno mostrato un’origine di mantello per la CO2, mentre quelli nelle peridotiti di El Hierro dai valori tipici di mantello. L'accuratezza delle misure è stata verificata tramite spettrometria di massa. Questa ha dimostrato che i valori di δ13CCO2 calcolati erano accurati, e consentivano di modellare la variazione isotopica a scala minerale. L’applicabilità della micro-spettroscopia Raman come densimetro per i fluidi a CO2 è stata precedentemente studiata. Molte equazioni di densimetro calcolano d differenti per gli stessi Δ, con distribuzione grafica bimodale, la cui origine non è stata ben compresa. L'origine di questa distribuzione è stata studiata nel presente lavoro calcolando la d di 40 FI a CO2 pura, provenienti da El Hierro, mediante microtermometria. I Δ sono stati misurati acquisendo spettri Raman con una procedura simile a quella adottata per altri densimetri, con risoluzione spettrale per px ≈1,50 cm-1/px. La distribuzione dei dati Δ-d è stata fittata al meglio con un'equazione polinomiale di III°, permettendo di calcolare le d della CO2 con un errore di ±0.015 g/cm3. L’equazione plottava con quelle ottenute mediante una risoluzione spettrale per px simile. Gli intervalli di confidenza al 95% della distribuzione Δ-d per tutte le equazioni sono stati calcolati mediante un algoritmo statistico. I CI hanno permesso di valutare l'accuratezza dei valori Δ-d e di definire un punto di cut-off al di sotto del quale la potenza di stima della d era bassa. Per tutti i densimetri, il punto di cut-off corrispondeva al punto in cui le distanze relative dei CI erano <7.5% (coincidenti con CO2 gassosa a P-T ambiente). Il confronto tra CI al 95% delle equazioni a bassa ed alta risoluzione spettrale per px ha mostrato che densimetri con risoluzione calcolano d statisticamente equivalente con una confidenza del 95%. Al contrario, densimetri con risoluzione diversa calcolano d non confrontabili. I risultati ottenuti hanno consentito di proporre un metodo preliminare per calcolare in situ i δ13CCO2 con una precisione ≈±2% per il 95% delle analisi. Inoltre, questi hanno migliorato la conoscenza della distribuzione Δ-d dei densimetri Raman, indicando che d di CO2 calcolate per mezzo di equazioni con risoluzione spettrale simile sono statisticamente equivalenti al 95% di confidenza per FI aventi d vicino e al di sopra del punto critico di CO2.
This thesis investigates the applicability of Raman micro-spectroscopy for CO2 density (d) and δ13CCO2 values calculations to improve characterisation of CO2 Earth’s fluid trapped as fluid inclusions (FI) in peridotites. Based on the properties of CO2 Raman spectrum, where the distance of two main vibrations is d-dependent and 13CO2 and 12CO2 vibrations are present, Raman micro-spectroscopy has the potential to become a complementary technique for in situ characterisation of CO2 FI, allowing to better understand the C transport mechanisms within Earth. The calculation of CCO2 isotopic composition by mean of Raman micro-spectroscopy is possible due to the proportionality between 13CO2 and 12CO2 areas with their molar concentration. Calculation of area ratios requires precision at 4th decimal place to obtain δ13CCO2 values representative of Earth’s natural reservoirs. Raman spectra are affected by unavoidable random effects that reduce area measurements’ precision. 42 high-d CO2-pure FI from Lake Tana region and El Hierro have been analysed. For each inclusion, two sets of spectra have been acquired by mean of different acquisition times. Among the 84 set of measurements, 23 were characterised by 13CO2/12CO2 area ratios differing more than one order of magnitude one another. These have been removed from dataset. 95% of remaining 61 sets were characterised by area ratios reproducibility <≈4‰, allowing to calculate FI δ13CCO2 values with precision <±≈2‰. Only few analyses were characterised by lower precision. Calculated δ13CCO2 values for FI trapped in peridotites from Lake Tana region showed CO2 mantle origin, while for those in peridotites from El Hierro differed from mantle isotopic signature. Accuracy of measurement has been checked by bulk measurements, proving that calculated δ13CCO2 values were accurate, and allowing to model δ13CCO2 variations at single mineral scale. The adoption of Raman micro-spectroscopy for calculating CO2 fluid d has been previously investigated. Many densimeter equations calculate different d for the same Δ values, with a bimodal graphic distribution, whose origin was not well understood. The origin of this distribution has been investigated in present work by calculating the d of 40 CO2-pure FI trapped in mantle xenoliths from El Hierro by mean of microthermometry. CO2 FI Δ values have been measured by acquiring Raman spectra applying analytical parameters common to those adopted for other densimeter equations, with spectral per px resolution ≈1.50 cm-1/px. A 3rd order polynomial equation best fitted obtained Δ-d data distribution. Equation calculates CO2 d with an error of ±0.015 g/cm3, and plots with those obtained by mean of a similar spectral per px resolution. The 95% confidence interval (CI) of Δ-d distribution for all the equations has been calculated by a bootstrapping statistical algorithm. CIs allowed to assess the accuracy of measured Δ-d values and define a cut-off point below which the CO2 d estimation power is low. For all the densimeters, cut-off point has been set where the relative distances of computed CIs were <7.5%, which corresponded for all the equations to gas-like CO2 at ambient conditions. The comparison of 95% CIs calculated for high and low spectral resolution per px equations showed that densimeters with similar spectral per px resolution calculate statistically equivalent CO2 d at 95% confidence. In contrast, densimeters with different resolution calculate incomparable CO2 d.Obtained results allowed to preliminarily propose an analytical procedure to calculate in situ δ13CCO2 with a precision of ≈±2% for 95% of the analyses. Moreover, these improved the knowledge about Δ-d distribution of Raman densimeters, indicating that CO2 d calculated by mean of equations having similar spectral resolution are statistically equivalent at 95% confidence for CO2 FI having d values near and above the CO2 critical point.

Investigación financiada por el proyecto del Ministerio de Ciencia e Innovación CGL2010-17108 (Inv. Principal S. Sánchez Moral) y ha sido posible gracias a una ayuda predoctoral (beca y contrato en prácticas) del programa JAE (Junta de Ampliación de Estudios, CSIC).

Ce travail de thèse est basé sur la mesure du dioxyde de carbone, CO2, et de son isotopologue stable δ13CO2 dans les bulles d'air emprisonnées dans la glace polaire (carotte EPICA Dome C en Antarctique, EDC). On s'intéresse aux transitions rapides entre périodes glaciaires et interglaciaires. Le δ13CO2 permet de départager l'origine du CO2 entre les sources océaniques ou terrestres.
Cette étude documente à haute résolution temporelle l'évolution du CO2 et du δ13CO2 pendant les deux dernières déglaciations. La dernière déglaciation est caractérisée par une augmentation en CO2 de 80 ppmv, accompagnée par une diminution en δ13CO2 de 0.6 ‰. Des amplitudes plus importantes sont observées durant la pénultième déglaciation (+110 ppmv CO2, accompagnés pas une diminution en δ13CO2 de 0.9 ‰).
Les mesures, interprétées avec deux modèles du cycle du carbone (BOXKIT et BICYCLE) sont cohérentes avec le scénario suivant. Dans un premier temps, un réchauffement de l'hémisphère sud initie une augmentation du CO2 atmosphérique. Ceci entraîne une réorganisation biologique et physique de l'océan austral qui diminue le δ13CO2. Enfin, cette réorganisation se propage vers le nord avec un impact retardé de la biosphère continentale, pendant le Bølling/Allerød (B/A).
Ces résultats obtenus pour la première fois dans la carotte EDC, ont permis de proposer un scénario sur les causes des déglaciations. Une série de tests, basée sur des glaces de différentes propriétés a fourni une validation de notre méthode d'extraction.

Abstract Geochemical analysis of gases produced during the drilling process is a common study on oil and gas exploration and development wells. This process typically includes the use of gas sample containers or other vessels that allow for single point samples to be collected for shipment to an offsite laboratory. Laboratories use high precision devices to obtain valuable information for reservoir characterization including stable carbon isotope ratios. In recent years there have been efforts to provide similar analyses during the drilling process, using ruggedized equipment suitable for wellsite deployment. This paper demonstrates that a Gas Chromatograph-Combustion-Isotope Ratio Mass Spectrometer (GC-C-IRMS) analyzer, using similar technology to what is most widespread in offsite laboratories (Dashti et al, 2018), can be successfully deployed to the rig site. This type of advanced gas analysis, commonly known as Mud Gas Isotope Logging (MGIL), provides continuous sampling of stable carbon isotopes of methane (δ13C1), ethane (δ13C2), and propane (δ13C3). The service, performed with a GC-C-IRMS analyzer, was proven and validated for an operator through two case studies. 98 The first case compares real time data with discrete gas sample tubes analyzed in an offsite laboratory. It shows how accurate results are possible, even with the presence of artificial gases generated by drill bit metamorphism (DBM) (Wenger et al, 2009). This example also demonstrates how the service enabled immediate analysis for operational decisions by indicating the presence of biodegraded thermogenic fluid. The second case study demonstrates how this wellsite service could corroborate the geological prognosis in a complex field influenced by salt tectonics. In this basin an upthrown reservoir changed the typical behavior observed in conventional wells of increased oil maturity with depth. Stable carbon isotope readings obtained in real time, integrated with cuttings analysis, indicated the presence of out of section lithology. This information allowed for estimating the thermogenic fluid maturity of reservoirs and diagnosis of geological formations that were out of sequence in terms of age (uplifted).