Origin and carbon isotope fractionation of CO2 in marine sour gas reservoirs in the Eastern Sichuan Basin

Liu, Quanyou; Jin, Zhijun; Wu, Xiaoqi; Liu, Wenhui; Gao, Bo; Zhang, Dianwei; Li, Jian; Hu, Anping

doi:10.1016/j.orggeochem.2014.01.012

Cited by 48 publications

(15 citation statements)

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“…These results suggest that TSR can alter both the carbon and hydrogen isotopic composition of gaseous alkane products, and even lead to a reversed trend of the carbon isotope series of CH 4 and C 2 H 6 for a mix of C 9 and MgSO 4 as the source material. This can result in similar isotopic compositions to those of H 2 S-bearing natural gas 45 . Liu et al 20 investigated carbonate gas systems in the Sichuan Basin of China and found different amounts of acid gases (CO 2 and H 2 S) in all marine strata.…”

Section: Discussionmentioning

confidence: 78%

“…These results indicate that the TSR can reduce the variation of δ 2 H–C 1 , possibly due to the similar hydrogen isotopic composition of the reaction product (C 1 gas) and that of the precursor and/or the involvement of hydrogen derived from water 21 . The δ 2 H–C n fractionation could not be accurately calculated because of a lack of the hydrogen isotopic composition of H 2 and H 2 S. However, TSR of crude oil in the presence of MgSO 4 greatly reduced the variation of δ 2 H–C 1 , which is consistent with the characteristics of H 2 S-bearing alkane gas in the reservoirs of the Sichuan Basin, China 45 . In general, hydrogen isotope fractionation during pyrolysis system may be more complicated than fractionation of carbon isotopes, because hydrogen contributes both to formation of alkane gas and H 2 , while also providing hydrogen for the formation of H 2 S. More importantly, the presence of water may provide an important hydrogen during pyrolysis 21 .…”

Section: Discussionmentioning

confidence: 88%

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Fractionation of carbon and hydrogen isotopes of TSR-altered gas products under closed system pyrolysis

Liu

Peng

Meng

et al. 2020

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Thermochemical sulfate reduction (TSR) is common in marine carbonate gas reservoirs, leading to complicated isotope characteristics of TSR-altered gas. This study aims to better understand how TSR affects the geochemical and isotopic compositions of alkanes in pyrolysis products. Pyrolysis of TSR were conducted with crude oil, nonane (C 9 ) and methylnaphthalene (MN) in the presence of MgSO 4 solution at temperatures of 350 °C, 360 °C, and 370 °C for different durations of 4–219 h in a closed system. Results show that carbon and hydrogen isotope compositions of alkane gas resulting from TSR (pyrolysis with crude oil and MgSO 4 ) became heavier with increasing carbon number, i.e., δ 13 C 1 < δ 13 C 2 < δ 13 C 3 and δ 2 H–C 1 < δ 2 H–C 2 < δ 2 H–C 3 . Compared with the δ 13 C 1 , δ 13 C 2 and δ 13 C 3 increased in a much wider range as heating continued. Carbon and hydrogen isotopes of alkane gas produced by TSR became heavier with increasing gas souring index. Values for δ 13 C 1 –δ 13 C 2 and δ 2 H–C 1 – δ 2 H–C 2 typically decreased as oil and C 9 underwent thermal cracking. Comparative experiments using C 9 in the presence of MgSO 4 produced partially reversed carbon isotope series (δ 13 C 1 > δ 13 C 2 ), which, for the first time, confirmed the ability of TSR to cause isotopic reversal from pyrolysis. The residual heavy alkanes gradually became 13 C-enriched during TSR, which increased δ 13 C 2 values and changed the partially reversed isotope sequence to a positive sequence (δ 13 C 1 < δ 13 C 2 ). The discovery of a partial reversal of the carbon isotope series of alkane gases through pyrolysis will further deepen the understanding of TSR-altered natural gas.

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Section: Discussionmentioning

confidence: 78%

Section: Discussionmentioning

confidence: 88%

Fractionation of carbon and hydrogen isotopes of TSR-altered gas products under closed system pyrolysis

Liu

Peng

Meng

et al. 2020

Sci Rep

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“…During TSR reactions at first, 32 S is produced as according to the required bond energy (Zhu et al 2005), and the generated H 2 S becomes progressively isotopically heavy as the process is continued. CO 2 produced during TSR processes should be primarily depleted in 13 C-isotope because it is derived from organic matter (e.g., Mougin et al 2007;Zhang et al 2008); however, as TSR continues, CO 2 becomes successively enriched in 13 C-isotope due to CO 2 dissolution in water, and subsequent carbonate minerals precipitation could increase the δ 13 C of residual CO 2 (Liu et al 2014). A similar situation is in wells 5 and 10, where isotopically heavy CO 2 is found (−2.9 and −3.6, respectively), occurs in larger concentrations (3.2 and 3.4 vol%, respectively) with respect to other studied gas samples (tables 1 and 2).…”

Section: Gas Composition and Isotopic Signaturesmentioning

confidence: 99%

Integrating geochemical and reservoir engineering approach to evaluate reservoir continuity: A case study from Foroozan field, Offshore Iran

et al. 2019

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The purpose of this study was to identify intra-reservoir compartmentalisation using geochemical and reservoir engineering evidences. On the basis of this approach, 11 gaseous samples, which belong to different wells producing from the Burgan reservoir of Foroozan field, were selected. Gas composition, gas isotopes and associated oil bulk properties were tested to determine the reservoir continuity through the Burgan reservoir. In addition, fluid contacts and properties are also used to investigate reservoir continuity. Regarding clear differences in gas composition such as hydrogen sulphide concentrations, at least two separate segments in the north and south of the reservoir were detected. Moreover, the percentages of the different gas components indicated two separate compartments. Other evidences such as C 1-C 4 alkane isotopic compositions and sulphur and nitrogen isotopic signatures confirmed the Burgan reservoir compartmentalisation. A number of petroleum bulk properties confirmed gradual variations that provide supplementary evidence on the reservoir-filling direction, signifying that fluids equilibrium had not been extended through the Burgan reservoir, laterally. Initial reservoir condition, different original water-oil contacts, solution gas-oil ratio at original pressure and bubble point pressure are other reservoir engineering evidences that support the Burgan reservoir compartmentalisation.

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“…According to identification indicators for CO 2 origins established by Dai et al [36], CO 2 is of organic origin if the CO 2 content is less than 15% and d 13 C co2 is less than À10‰, and CO 2 is of inorganic origin if the CO 2 content is greater than 60% or d 13 C co2 is greater than À8‰. The geochemical characteristics indicated that the CO 2 of the Huanglong Formation in the Sichuan Basin was of inorganic origin, and was mainly produced by carbonate rock dissolution by acid gases [37]. The CO 2 and H 2 S content of Well Tiandong 53 in the WBT gas field were 8.23% and 5.41%, respectively, and the d 13 C co2 value attained À1.6‰, results which are similar to the high sulfur-bearing natural gases from the Lower Triassic Feixianguan Formation and the Upper Permian Changxing Formation, indicating their carbon isotope values were probably influenced by TSR [37].…”

Section: Carbon Isotopic Compositionmentioning

confidence: 99%

Geochemical characteristics and geological significance of shale gas from the Lower Silurian Longmaxi Formation in Sichuan Basin, China

Gao

2016

Journal of Natural Gas Geoscience

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The shale of the Lower Silurian Longmaxi Formation has become a key target for shale gas exploration and development in China recently. The origin of carbon and hydrogen isotopic reversal in shale gas is discussed in this paper based on the analysis of the chemical components and stable isotope composition of natural gas in the Carboniferous Huanglong Formation sourced from Longmaxi Formation and Longmaxi shale gas. The shale gas was mainly composed of hydrocarbon gas in which the content of CH 4 was in the range of 95.52%e99.59%, C 2 H 6 0.23%e 0.72%, and C 3 H 8 0.0%e0.03%. The drying coefficient (C l /C le5 ) was more than 0.99, indicating typical dry gas. The values of d 13 C 1 , d 13 C 2 and d 13 C 3 ranged from À37.3‰ to À26.7‰, À42.8‰ to À31.6‰, and À43.5‰ to À33.1‰, respectively. The carbon isotope values indicated that the hydrocarbon gas was an oil-type gas. However, the reversal of carbon and hydrogen isotopes of hydrocarbon gases in shale gas occurred, i.e., d 13 C 1 > d 13 C 2 , dD 1 > dD 2 . The geochemical characteristic of high thermal maturity and carbon isotope reversal in the Longmaxi shale gas was similar to those of the Fayetteville shale gas in U.S. The Longmaxi shale gas is a mixture of gases from decomposition of kerogen at high thermal maturity and cracking of soluble organic matter retained within the shale, suggesting there is an abundance of shale gas to support high productivity.

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Origin and carbon isotope fractionation of CO2 in marine sour gas reservoirs in the Eastern Sichuan Basin

Cited by 48 publications

References 38 publications

Fractionation of carbon and hydrogen isotopes of TSR-altered gas products under closed system pyrolysis

Fractionation of carbon and hydrogen isotopes of TSR-altered gas products under closed system pyrolysis

Integrating geochemical and reservoir engineering approach to evaluate reservoir continuity: A case study from Foroozan field, Offshore Iran

Geochemical characteristics and geological significance of shale gas from the Lower Silurian Longmaxi Formation in Sichuan Basin, China

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