Constrain on Oil Recovery Stage during Oil Shale Subcritical Water Extraction Process Based on Carbon Isotope Fractionation Character

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.

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An experimental study of carbon-isotope fractionation between diet, hair, and feces of mammalian herbivores

Canadian Journal of Zoology ◽

10.1139/z03-066 ◽

2003 ◽

Vol 81 (5) ◽

pp. 871-876 ◽

Cited By ~ 198

Author(s):

Matt Sponheimer ◽

Todd Robinson ◽

Linda Ayliffe ◽

Ben Passey ◽

Beverly Roeder ◽

...

Keyword(s):

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Fractionation ◽

Cynodon Dactylon ◽

Isotope Composition ◽

Mammalian Herbivores ◽

Carbon Isotope Fractionation ◽

Tropical Environments ◽

The Mean ◽

Lama Pacos

The carbon-isotope composition of hair and feces offers a glimpse into the diets of mammalian herbivores. It is particularly useful for determining the relative consumption of browse and graze in tropical environments, as these foods have strongly divergent carbon-isotope compositions. Fecal δ13C values reflect the last few days consumption, whereas hair provides longer term dietary information. Previous studies have shown, however, that some fractionation occurs between dietary δ13C values and those of hair and feces. Accurate dietary reconstruction requires an understanding of these fractionations, but few controlled-feeding studies have been undertaken to investigate these fractionations in any mammalian taxa, fewer still in large mammalian herbivores. Here, we present data from the first study of carbon-isotope fractionation between diet, hair, and feces in multiple herbivore taxa. All taxa were fed pure alfalfa (Medicago sativa) diets for a minimum period of 6 months, at which point recently grown hair was shaved and analyzed for carbon isotopes. The mean observed diethair fractionation was +3.2, with a range of +2.7 to +3.5. We also examined dietfeces fractionation for herbivores on alfalfa and bermudagrass (Cynodon dactylon) feeds. The mean dietfeces fractionation for both diets was 0.8, with less fractionation for alfalfa (0.6) than bermudagrass (1.0). Fecal carbon turnover also varies greatly between taxa. When diets were switched, horse (Equus caballus) feces reflected the new diet within 60 h, but alpaca (Lama pacos) feces did not equilibrate with the new diet for nearly 200 h. Thus, fecal carbon isotopes provide far greater dietary resolution for hindgut-fermenting horses than foregut-fermenting alpacas.

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The Carbon-Isotope Record of the Sub-Seafloor Biosphere

Geosciences ◽

10.3390/geosciences9120507 ◽

2019 ◽

Vol 9 (12) ◽

pp. 507 ◽

Cited By ~ 3

Author(s):

Patrick Meister ◽

Carolina Reyes

Keyword(s):

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Fractionation ◽

Dissolved Inorganic Carbon ◽

Isotopic Signature ◽

Enzymatic Reactions ◽

Deep Biosphere ◽

Geological Time ◽

Isotopic Signatures ◽

Carbon Isotope Fractionation

Sub-seafloor microbial environments exhibit large carbon-isotope fractionation effects as a result of microbial enzymatic reactions. Isotopically light, dissolved inorganic carbon (DIC) derived from organic carbon is commonly released into the interstitial water due to microbial dissimilatory processes prevailing in the sub-surface biosphere. Much stronger carbon-isotope fractionation occurs, however, during methanogenesis, whereby methane is depleted in 13C and, by mass balance, DIC is enriched in 13C, such that isotopic distributions are predominantly influenced by microbial metabolisms involving methane. Methane metabolisms are essentially mediated through a single enzymatic pathway in both Archaea and Bacteria, the Wood–Ljungdahl (WL) pathway, but it remains unclear where in the pathway carbon-isotope fractionation occurs. While it is generally assumed that fractionation arises from kinetic effects of enzymatic reactions, it has recently been suggested that partial carbon-isotope equilibration occurs within the pathway of anaerobic methane oxidation. Equilibrium fractionation might also occur during methanogenesis, as the isotopic difference between DIC and methane is commonly on the order of 75‰, which is near the thermodynamic equilibrium. The isotopic signature in DIC and methane highly varies in marine porewaters, reflecting the distribution of different microbial metabolisms contributing to DIC. If carbon isotopes are preserved in diagenetic carbonates, they may provide a powerful biosignature for the conditions in the deep biosphere, specifically in proximity to the sulphate–methane transition zone. Large variations in isotopic signatures in diagenetic archives have been found that document dramatic changes in sub-seafloor biosphere activity over geological time scales. We present a brief overview on carbon isotopes, including microbial fractionation mechanisms, transport effects, preservation in diagenetic carbonate archives, and their implications for the past sub-seafloor biosphere and its role in the global carbon cycle. We discuss open questions and future potentials of carbon isotopes as archives to trace the deep biosphere through time.

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Carbon isotope fractionation by photosynthetic aquatic microorganisms: experiments with Synechococcus PCC7942, and a simple carbon flux model

Canadian Journal of Botany ◽

10.1139/b98-067 ◽

1998 ◽

Vol 76 (6) ◽

pp. 1109-1118 ◽

Cited By ~ 3

Author(s):

Jonathan Erez ◽

Anne Bouevitch ◽

Aaron Kaplan

Keyword(s):

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Fractionation ◽

Isotopic Fractionation ◽

Bisphosphate Carboxylase ◽

Carbon Isotope Fractionation ◽

Concentrating Mechanism ◽

Aquatic Microorganisms ◽

Synechococcus Pcc7942 ◽

Flux Model

Stable carbon isotopes (12C and 13C) are widely used to trace biogeochemical processes in the global carbon cycle. Natural fractionation of carbon isotopes is mainly due to the discrimination of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) against 13C during photosynthesis. In marine and other aquatic microorganisms, this fractionation is lowered when the dissolved CO2 (CO2(aq)) is decreasing, but the underlying mechanisms are poorly understood. Cultured Synechococcus PCC7942 showed maximum isotopic fractionations of -33omicron (in delta 13C units) relative to the total inorganic carbon (Ci) when CO2(aq) is above 30 m M. As the culture grew, pH increased, CO2(aq) was lower than 1 m M, and the Ci concentrating mechanism was induced although the Ci was above 3 mM. The isotopic fractionation was drastically reduced to values of -1 to -3 omicron relative to Ci. A simple carbon isotope flux model suggests that during the first stages of the experiment the total uptake (F1) was roughly three- to four-fold greater than the photosynthetic net accumulation (F2). When the Ci concentrating mechanism was induced, the leakage of CO2 from the cells declined, the cells started to utilize HCO3- and the F1/F2 ratio decreased to values close to 1. Based on this model the isotopic variability of oceanic phytoplankton suggests that the F1/F2 ratio may be above 3 in high latitudes and ~1.1 in equatorial waters, where the Ci concentrating mechanism is probably induced. Attempts to reconstruct past atmospheric CO2 levels and paleoproductivity should take into account the effects of the Ci concentrating mechanism on the isotopic fractionation of aquatic primary producers.Key words: carbon concentrating mechanism, carbon isotope fractionation, CO2, photosynthesis.

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Carbon isotope fractionation in various forms of biogenic organic matter: I. Partitioning of carbon isotopes between the main polymers of higher plant biomass

Geochemistry International ◽

10.1134/s0016702910120013 ◽

2010 ◽

Vol 48 (12) ◽

pp. 1157-1165 ◽

Cited By ~ 11

Author(s):

L. A. Kodina

Keyword(s):

Organic Matter ◽

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Fractionation ◽

Plant Biomass ◽

Higher Plant ◽

Carbon Isotope Fractionation

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Anaerobic methane oxidation by nitrate: kinetic isotope effect

Environmental Dynamics and Global Climate Change ◽

10.17816/edgcc10534 ◽

2018 ◽

Vol 10 (1) ◽

Author(s):

Vasiliy A. Vavilin

Keyword(s):

Dynamic Model ◽

Carbon Isotope ◽

Carbon Isotopes ◽

Isotope Effect ◽

Isotope Fractionation ◽

Kinetic Isotope Effect ◽

Stable Carbon Isotopes ◽

Stable Carbon ◽

Fractionation Factor ◽

Kinetic Isotope

The ratio of stable carbon isotopes (13C/12C) in different environments serves as a significant limitation in estimating the global balance of methane [Hornibrook et al., 2000]. In this case, the value of 13C/12C largely depends on the kinetic isotope effect associated with the metabolism of microorganisms that produce and consume CH4. The article suggests a dynamic model of the processes of methane formation and its anaerobic oxidation with nitrate by methanotrophic denitrifying microorganisms (DAOM), which allowed estimating the fractionation factor of stable carbon isotopes. In the experiment with peat from the minerotrophic bog [Smemo, Yavitt, 2007], the dynamics of the amount of methane and was measured. The dynamic model showed that the introduction of nitrate leads to a slow decrease in the partial pressure of methane. Since methane in the DAOM process is a substrate, methane is enriched with heavier carbon 13C in the system under study. This leads to an increase in the value . The carbon isotope fractionation factor during methane oxidation with nitrate was equal to 1.018 and comparable with the fraction of carbon isotope fractionation in the process of acetoclastic methanogenesis (1.01). Model calculations have shown that during incubation the apparent fractionation factor of carbon isotopes with the simultaneous formation of methane and DAOM slowly decreases. The ratio of 13C/12C isotopes in dissolved and gaseous methane practically does not differ. The model showed that an increase in the initial concentration of nitrate increases the rate of DAOM, which leads to a decrease in the concentration of dissolved methane. In this case, the value of 13C/12C increases. In field studies, Shi et al. (2017) showed that the presence of DAOM in peat bogs in which fertilizers penetrate can be controlled by the amount of nitrate used and the depth of penetration into the anoxic layer. Two MATLAB files describing DAOM are attached to the article.

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VOLCANISM DRIVEN CARBON ISOTOPE FRACTIONATION ACROSS THE WUCHIAPINGIAN-CHANGHSINGIAN BOUNDARY INTERVAL: IMPLICATIONS FROM 187OS/188OS ISOTOPE STRATIGRAPHY

10.1130/abs/2018am-316949 ◽

2018 ◽

Author(s):

Zeyang Liu ◽

◽

David Selby ◽

Hua Zhang ◽

Quanfeng Zheng ◽

...

Keyword(s):

Carbon Isotope ◽

Isotope Fractionation ◽

Carbon Isotope Fractionation ◽

Isotope Stratigraphy

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Cyclic Subcritical Water Injection into Bazhenov Oil Shale: Geochemical and Petrophysical Properties Evolution Due to Hydrothermal Exposure

Energies ◽

10.3390/en14154570 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4570

Author(s):

Aman Turakhanov ◽

Albina Tsyshkova ◽

Elena Mukhina ◽

Evgeny Popov ◽

Darya Kalacheva ◽

...

Keyword(s):

Energy Demand ◽

Oil Shale ◽

Oil And Gas ◽

Subcritical Water ◽

Pore Space ◽

Water Injection ◽

Microstructural Properties ◽

Gas Generation ◽

Geochemical Parameters

In situ shale or kerogen oil production is a promising approach to developing vast oil shale resources and increasing world energy demand. In this study, cyclic subcritical water injection in oil shale was investigated in laboratory conditions as a method for in situ oil shale retorting. Fifteen non-extracted oil shale samples from Bazhenov Formation in Russia (98 °C and 23.5 MPa reservoir conditions) were hydrothermally treated at 350 °C and in a 25 MPa semi-open system during 50 h in the cyclic regime. The influence of the artificial maturation on geochemical parameters, elastic and microstructural properties was studied. Rock-Eval pyrolysis of non-extracted and extracted oil shale samples before and after hydrothermal exposure and SARA analysis were employed to analyze bitumen and kerogen transformation to mobile hydrocarbons and immobile char. X-ray computed microtomography (XMT) was performed to characterize the microstructural properties of pore space. The results demonstrated significant porosity, specific pore surface area increase, and the appearance of microfractures in organic-rich layers. Acoustic measurements were carried out to estimate the alteration of elastic properties due to hydrothermal treatment. Both Young’s modulus and Poisson’s ratio decreased due to kerogen transformation to heavy oil and bitumen, which remain trapped before further oil and gas generation, and expulsion occurs. Ultimately, a developed kinetic model was applied to match kerogen and bitumen transformation with liquid and gas hydrocarbons production. The nonlinear least-squares optimization problem was solved during the integration of the system of differential equations to match produced hydrocarbons with pyrolysis derived kerogen and bitumen decomposition.

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Carbon Isotope Fractionation during the Formation of CO2 Hydrate and Equilibrium Pressures of 12CO2 and 13CO2 Hydrates

Molecules ◽

10.3390/molecules26144215 ◽

2021 ◽

Vol 26 (14) ◽

pp. 4215

Author(s):

Hiromi Kimura ◽

Go Fuseya ◽

Satoshi Takeya ◽

Akihiro Hachikubo

Keyword(s):

Carbon Isotope ◽

Isotope Fractionation ◽

Small Difference ◽

Hydrate Formation ◽

Formation Temperature ◽

Carbon Isotope Fractionation ◽

Unit Cell Size ◽

Naturally Occurring ◽

Three Phase ◽

The Difference

Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO2 hydrates. We investigated carbon isotope fractionation during CO2 hydrate formation and measured the three-phase equilibria of 12CO2–H2O and 13CO2–H2O systems. From a crystal structure viewpoint, the difference in the Raman spectra of hydrate-bound 12CO2 and 13CO2 was revealed, although their unit cell size was similar. The δ13C of hydrate-bound CO2 was lower than that of the residual CO2 (1.0–1.5‰) in a formation temperature ranging between 226 K and 278 K. The results show that the small difference between equilibrium pressures of ~0.01 MPa in 12CO2 and 13CO2 hydrates causes carbon isotope fractionation of ~1‰. However, the difference between equilibrium pressures in the 12CO2–H2O and 13CO2–H2O systems was smaller than the standard uncertainties of measurement; more accurate pressure measurement is required for quantitative discussion.

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