Geochemical anomalies in the Lower Silurian shale gas from the Sichuan Basin, China: Insights from a Rayleigh-type fractionation model

Feng, Ziqi; Hao, Fang; Dong, Dazhong; Zhou, Shangwen; Wu, Wei; Xie, Chengliang; Cai, Yuwen; Li, Zhixin

doi:10.1016/j.orggeochem.2020.103981

Cited by 23 publications

(11 citation statements)

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“…When plotting the δ 13 C 1 versus gas wetness, gases from Weirong, Weiyuan, Barnett, and Fayetteville have a good linear relationship, while gases from Taiyang and Jiaoshiba are characterized by an enrichment of 13 C in methane and thus shift away from the linear maturity trend (Figure 7A). The 13 C-enriched methane was considered to be a late-stage methane and result from Rayleigh-type isotopic fractionation of ethane (Feng et al, 2020); however, such a mechanism may not satisfy the mass and isotopic balance requirements (Xia and Gao, 2018). In the southern Sichuan Basin, geological conditions are Lines of Type II kerogen from Berner and Faber (1996) and Huang et al (2016) are also shown.…”

Section: Carbon Isotope Of Methanementioning

confidence: 99%

“…From the Weirong gas field to the Taiyang gas field, the equivalent Ro% increases from 2.25% to 3.45% (Wang et al, 2019;Liang et al, 2021;Zou et al, 2021), while the CO 2 content decreases from 2.05% to 0.10%. The carbon isotope of CO 2 in the Jiaoshiba area varies from −5.8‰ to 10.4‰ (average = 3.7‰) (Feng et al, 2020), which was considered to be the product of thermal metamorphism of carbonate minerals (Dai et al, 2022). Carbonate minerals are abundant in the Wufeng-Longmaxi shale (Dai et al, 2014a;Dai et al, 2016b), and with increasing thermal maturity, thermal metamorphism will generate more CO 2 .…”

Section: Fischer-tropsch-type Synthesis Of Hydrocarbonmentioning

confidence: 99%

“…Due to the kinetic isotopic fractionation effects (Lorant et al, 1998;Tang et al, 2000), primary gases are usually characterized by the normal carbon isotopic trend, that is, δ 13 C 1 < δ 13 C 2 < δ 13 C 3 . However, recently, a number of studies have documented a depletion of 13 C in ethane and propane and an enrichment of 13 C in methane at high maturity, resulting in the carbon isotopic reversal between methane and ethane (δ 13 C 1 > δ 13 C 2 ) (Ferworn et al, 2008;Burruss and Laughrey, 2010;Rodriguez and Philp, 2010;Zumberge et al, 2012;Hao and Zou, 2013;Tilley and Muehlenbachs, 2013;Dai et al, 2014aDai et al, , 2016bDai et al, , 2017Zhang et al, 2018b;Liu et al, 2018;Ni et al, 2018;Xia and Gao, 2018;Feng et al, 2020). Zumberge et al (2012) demonstrated a reversed carbon isotopic maturity trend in ethane and propane in gases from Barnett and Fayetteville shales, with thermal maturity (Ro%) over 1.5%.…”

Section: Introductionmentioning

confidence: 99%

“…One common feature of these carbon isotopic anomalies is that they occur at relatively high temperatures. To date, many studies have been carried out to investigate the mechanisms for the carbon isotopic characteristics of shale gases (Ferworn et al, 2008;Burruss and Laughrey, 2010;Rodriguez and Philp, 2010;Zumberge et al, 2012;Hao and Zou, 2013;Xia et al, 2013;Gao et al, 2014;Zhang et al, 2018b;Xia and Gao, 2018;Feng et al, 2020;Mi et al, 2022). Moreover, isotopic reversal may correlate with the gas generation potential, and the reversal magnitude may correspond to the amount of gas retained in the shale (Tilley et al, 2011;Feng et al, 2018;Wang et al, 2021;Zhao et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

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Geochemical Characteristics and Origin of Shale Gases From Sichuan Basin, China

Dong

Yao

et al. 2022

Front. Earth Sci.

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Natural gases from the Taiyang (shallow), Jiaoshiba (middle), and Weirong (deep) shale gas fields in the southern Sichuan Basin were analyzed for molecular and stable carbon isotopic compositions to investigate the geochemical characteristics and gas origins. All the gases belong to shale gas from the Upper Ordovician–Lower Silurian shale and are dominated by methane with gas wetness generally less than 0.83%. The δ13C1 values are −28.5‰, −30.3‰, and −35.2‰ in Taiyang, Jiaoshiba, and Weirong shale gas fields, respectively. The extremely high thermal maturity is the controlling factor for the enrichment of 13C in methane, with a minor contribution from the heavy carbon isotope of the organic matter in the Ordovician Wufeng Formation. Fischer–Tropsch-type synthesis of hydrocarbon gas from CO2 and H2 contributes to the increase of wet gas, which results in the offset from the δ13C1∼wetness linear trend in the Taiyang and Jiaoshiba gas fields. Methane, ethane, and propane in the Taiyang shale gas field have increasing δ13C values with increasing burial depth, which is mainly caused by diffusive migration. All gases are characterized by a complete carbon isotopic reversal trend (δ13C1 > δ13C2 > δ13C3), and it is mainly caused by the reversible free-radical reactions with the conversion from alkane to alkyl groups, with some contribution from the Fischer–Tropsch-type synthesis. The results of this study will improve our understanding of the geochemical characteristics of shale gases from different burial depths and have important implications for future shale gas exploration in the deep and shallow layers.

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Section: Carbon Isotope Of Methanementioning

confidence: 99%

Section: Fischer-tropsch-type Synthesis Of Hydrocarbonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geochemical Characteristics and Origin of Shale Gases From Sichuan Basin, China

Dong

Yao

et al. 2022

Front. Earth Sci.

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“…Total organic carbon (TOC) is usually the main indicator for evaluating the abundance of source rocks (Li et al, 2016;Liu et al, 2019;Feng et al, 2020). The TOC content of the shale in the Dongyuemiao shale of Well FY10 ranges from 0.77 to 3.13%, with an average value of 1.67% (Table 2).…”

Section: Organic Geochemical and Physical Characteristicsmentioning

confidence: 99%

Heterogeneity Characteristics of Lacustrine Shale Oil Reservoir Under the Control of Lithofacies: A Case Study of the Dongyuemiao Member of Jurassic Ziliujing Formation, Sichuan Basin

et al. 2021

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The lacustrine shale in the Dongyuemiao Member of the Fuling area, Sichuan Basin, is widely distributed and has huge shale oil resource potential. It is one of the important replacement areas for shale oil exploration in China. To investigate the key shale oil evaluation well, Well FY10, in the Fuling area, X-ray diffraction (XRD) mineral analysis, Rock-Eval, argon ion polishing-scanning electron microscope (SEM), Mercury injection capillary pressure (MICP), and low pressure nitrogen adsorption were launched to determine the heterogeneity of the pore system in the lacustrine shale of the Dongyuemiao Member. The mineral composition exhibits a high degree of heterogeneity, and the shale can be divided into two main lithofacies: argillaceous shale and mixed shale. The porosity ranges from 2.95 to 8.43%, and the permeability ranges from 0.05 to 1.07 × 10−3 μm2. The physical properties of mixed shale are obviously better than those of argillaceous shale. Inorganic mineral pores, such as linear pores between clay minerals and calcite dissolution pores, are mainly developed, while a small amount of organic pores can be observed. The average total pore volume (Vp) is 0.038 ml/g with an average specific surface area of 5.38 m2/g. Mesopores provide the main Vp (average 61.72%), and micropores provide mostly specific surface area. TOC imposes a strong controlling effect on the development of micropores. Clay minerals are the main contributors to mesopores and macropores. The organic-inorganic interaction during the process of diagenesis and hydrocarbon generation controls the formation of shale pore systems.

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