Stable isotope reversal and evolution of gas during the hydrous pyrolysis of continental kerogen in source rocks under supercritical conditions

Wu, Yuandong; Zhang, Zhongning; Sun, Liuyang; Li, Yuanju; Zhang, Mingzheng; Ji, Liming

doi:10.1016/j.coal.2019.03.004

Cited by 29 publications

(14 citation statements)

References 42 publications

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“…Carbon isotopes produced during the thermal cracking of organic matter are useful for assigning the degree of gas recovery with water presence [45]. This is mainly based on the detection of the carbon isotope "rollover point" (1.5%R o ), which correlates well with the highest production of hydrocarbon gases [23], or the "reversal point", which needs an even higher maturity with a %R o always higher than 2.0 [46]. However, those points are all beyond the highest oil generation area and were not discovered in our low time (0-100 h) oil shale subcritical water recovery process (Figure 4).…”

Section: Carbon Isotopes Charactermentioning

confidence: 99%

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

et al. 2021

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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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Section: Carbon Isotopes Charactermentioning

confidence: 99%

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

et al. 2021

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“…The carbon isotope values were reported as δ-values, which are expressed as δ sample = (R sample /R standard −1) × 1000 (‰) (where R denotes the ratio of 13 C/ 12 C). The δ 13 C values were normalized to the Pee Dee Belemnite (PDB) [29,43].…”

Section: Simulation Experimentsmentioning

confidence: 99%

“…Thus, this pyrolysis experiment could be seen as a continuous thermal evolution process with increasing maturity. Next, we used the value of the measured Ro to replace the simulated temperatures [29,43].…”

Section: Pyrolysis Productsmentioning

confidence: 99%

“…In addition, the experimental error range of ±0.5‰ for carbon isotope analysis was also considered in this analysis [43]. Overall, the δ 13 C kerogen0 < δ 13 C kerogenr and δ 13 C bitumen0 < δ 13 C bitumen0+r , and the former degree of fractionation (δ 13 C kerogenr − 13 C kerogen0 = 0.1-0.8, the mean value = 0.5) was less than the latter degree of fractionation (δ 13 C bitumen0+r − δ 13 C bitumen0 = 0.1-1.3, the mean value = 1.11), implying that kerogen and bitumen as reactants in the thermal evolution process would become heavy at their corresponding carbon isotope.…”

Section: The Range the Range Linearmentioning

confidence: 99%

“…Simultaneously, the differences in organic matter with specific sources could be corrupted or integrated by the measured compositions of bulk isotopes and molecules [15]. Moreover, studying the characteristics of carbon isotopes can reveal information on parent material sources and also assess natural gas with different origins and thermal evolution degrees [39][40][41][42][43]. Thus, it is of great significance to comprehensively study the carbon isotopic composition of kerogen, bitumen, and gas-liquid products during thermal evolution.…”

Section: Introductionmentioning

confidence: 99%

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Evidence from the Changing Carbon Isotopic of Kerogen, Oil, and Gas during Hydrous Pyrolysis from Pinghu Formation, the Xihu Sag, East China Sea Basin

Cao

et al. 2021

Energies

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Semi-open hydrous pyrolysis experiments on coal-measure source rocks in the Xihu Sag were conducted to investigate the carbon isotope evolution of kerogen, bitumen, generated expelled oil, and gases with increasing thermal maturity. Seven corresponding experiments were conducted at 335 °C, 360 °C, 400 °C, 455 °C, 480 °C, 525 °C, and 575 °C, while other experimental factors, such as the heating time and rate, lithostatic and hydrodynamic pressures, and columnar original samples were kept the same. The results show that the simulated temperatures were positive for the measured vitrinite reflectance (Ro), with a correlation coefficient (R2) of 0.9861. With increasing temperatures, lower maturity, maturity, higher maturity, and post-maturity stages occurred at simulated temperatures (Ts) of 335–360 °C, 360–400 °C, 400–480 °C, and 480–575 °C, respectively. The increasing gas hydrocarbons with increasing temperature reflected the higher gas potential. Moreover, the carbon isotopes of kerogen, bitumen, expelled oil, and gases were associated with increased temperatures; among gases, methane was the most sensitive to maturity. Ignoring the intermediate reaction process, the thermal evolution process can be summarized as kerogen0(original) + bitumen0(original)→kerogenr (residual kerogen) + expelled oil (generated) + bitumenn+r (generated + residual) + C2+(generated + residual) + CH4(generated). Among these, bitumen, expelled oil, and C2-5 acted as reactants and products, whereas kerogen and methane were the reactants and products, respectively. Furthermore, the order of the carbon isotopes during the thermal evolution process was identified as: δ13C1 < 13C2-5 < δ13Cexpelled oil < δ13Cbitumen < δ13Ckerogen. Thus, the reaction and production mechanisms of carbon isotopes can be obtained based on their changing degree and yields in kerogen, bitumen, expelled oil, and gases. Furthermore, combining the analysis of the geochemical characteristics of the Pinghu Formation coal–oil-type gas in actual strata with these pyrolysis experiments, it was identified that this area also had substantial development potential. Therefore, this study provides theoretical support and guidance for the formation mechanism and exploration of oil and gas based on changing carbon isotopes.

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Evolution mechanism of Pinghu Formation coal-measure source rock from the Xihu Sag, East China Sea basin: Evidence from carbon isotopic evolution of kerogen, oil, and gas during hydrous pyrolysis

Cao

Ye²,

et al. 2021

Preprint

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Stable isotope reversal and evolution of gas during the hydrous pyrolysis of continental kerogen in source rocks under supercritical conditions

Cited by 29 publications

References 42 publications

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

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

Evidence from the Changing Carbon Isotopic of Kerogen, Oil, and Gas during Hydrous Pyrolysis from Pinghu Formation, the Xihu Sag, East China Sea Basin

Evolution mechanism of Pinghu Formation coal-measure source rock from the Xihu Sag, East China Sea basin: Evidence from carbon isotopic evolution of kerogen, oil, and gas during hydrous pyrolysis

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