Pyrobitumen in South China: Organic petrology, chemical composition and geological significance

Yang, Chengyu; Ni, Zhiyong; Li, Meijun; Wang, Tieguan; Chen, Zhonghong; Hong, Haitao; Tian, Xiaobo

doi:10.1016/j.coal.2018.01.014

Cited by 35 publications

(35 citation statements)

References 61 publications

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“…In addition, the content of bitumen in the reservoir and natural gas production has good correlation (Wei et al, ). It is consistent with the previous conclusion that the natural gas came from the cracking of paleo‐oil (Pan, Jiang, Liu, Zhang, & Zhu, ; Wei et al, ; Yang et al, ; Zhu et al, ; Zhu et al, ; Zou et al, ). Therefore, the source of paleo‐oil could be inferred by the chemical nature of the bitumen indicated by the REEs and trace element geochemistry combined with petrographic observations.…”

Section: Discussionsupporting

confidence: 92%

“…This is the largest gas reserve originating from the oldest marine source rocks in China and is also the first commercial discovery of primary gas accumulations in the Precambrian sediments in the world (Zhu, Wang, Xie, Xie, & Liu, ). The Sinian–Cambrian gas reservoirs are believed to have experienced an initial accumulation of paleo‐oil during the Paleozoic, gas generation from the cracking of the paleo‐oil accumulations during the Mesozoic, and the remigration and adjustment since the Mesozoic–Cenozoic (Du et al, ; Yang et al, ; Zhu et al, ; Zou et al, ). Numerous studies on potential hydrocarbon sources have been conducted in the Sinian and Cambrian reservoirs of the region.…”

Section: Introductionmentioning

confidence: 99%

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Trace element characterization of bitumen constraints on the hydrocarbon source of the giant gas field in Sichuan Basin, South China

Chen

et al. 2018

Geological Journal

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The exploration of high production, natural gas wells (>10 6 m 3 /d) has been extremely successful in the Gaoshiti and Moxi areas of the Leshan-Longnvsi paleo-uplift, in the west-central Sichuan Basin. This paper focuses on the Sinian and Cambrian reservoirs from the Gaoshiti and Moxi areas, where a dataset of new trace elements in bitumen and potential source rock is reported and where hydrocarbon-source correlation is attempted based on trace elements characteristics of the 12 potential source rocks and 22 bitumen samples. Results show that the bitumen from the three reservoirs can be distinguished from each other using trace element distribution patterns and redox-and provenance-sensitive elemental ratios. Bitumen in the second and fourth members of the Sinian Dengying Formation were derived primarily from the third member of the source rocks of the Dengying Formation, which represents a selfsourced paleo-petroleum system. In contrast, bitumen in the reservoirs of the Cambrian Longwangmiao Formation is derived from the Cambrian Qiongzhusi Formation and third member of Dengying Formation. The trace element method used in this study improves our understanding of the complex hydrocarbon-source relation and confirm the potential target for petroleum exploration in the study area.

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Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Trace element characterization of bitumen constraints on the hydrocarbon source of the giant gas field in Sichuan Basin, South China

Chen

et al. 2018

Geological Journal

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“…Furthermore, the W-type fluid inclusions are heavily distributed in the boundaries between the “cloudy centers” and the “clear rims”. This feature suggests that the fluid inclusions in the II-dolomite are related to the precipitation of the dolomite 21 , 53 . The homogenization temperatures of the fluid inclusions in the II-dolomite range from 107 to 212 °C.…”

Section: Discussionmentioning

confidence: 90%

“…The Sinian succession was then buried to a depth of 5015–5396 m. During the burial process, the oil may have pyrolyzed into pyrobitumen and gas, which are the most common materials filling the pore space in the reservoir 2 , 3 . The geochemistry evidences of pyrobitumen indicate that the gas field was generated by an in-situ burial pyrolysis of paleo-oil 20 , 21 . The Sinian reservoir is located at the top of the Dengying Formation (Z 2dn4 ) (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

A new genetic mechanism of natural gas accumulation

Yang

Wang

et al. 2018

Sci Rep

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Natural gas of organic origin is primarily biogenic or thermogenic; however, the formation of natural gas is occasionally attributed to hydrothermal activity. The Precambrian dolomite reservoir of the Anyue gas field is divided into three stages. Dolomite-quartz veins were precipitated after two earlier stages of dolomite deposition. Fluid inclusions in the dolomite and quartz are divided into pure methane (P-type), methane-bearing (M-type), aqueous (W-type), and solid bitumen-bearing (S-type) inclusions. The W-type inclusions within the quartz and buried dolomite homogenized between 107 °C and 223 °C. Furthermore, the trapping temperatures and pressures of the fluid (249 °C to 319 °C and 1619 bar to 2300 bar, respectively) are obtained from the intersections of the isochores of the P-type and the coeval W-type inclusions in the quartz. However, the burial history of the reservoir indicates that the maximum burial temperature did not exceed 230 °C. Thus, the generation of the natural gas was not caused solely by the burial of the dolomite reservoir. The results are also supported by the presence of paragenetic pyrobitumen and MVT lead-zinc ore. A coupled system of occasional invasion by hydrothermal fluids and burial of the reservoir may represent a new genetic model for natural gas accumulation in this gas field.

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“…This provides a differentiated heat source for overlying and underlying strata in different areas. The appearance of pyrobitumen in the Sinian-Cambrian reservoirs is clear evidence of an abrupt hydrothermal fluid event, which might correspond to the Emei mantle plume in the late Permian era [60,61]. WY and CN are in the Emeishan large igneous province region (Figure 3).…”

Section: Mixing Of Secondary Cracking Gasmentioning

confidence: 99%

Factors Affecting Shale Gas Chemistry and Stable Isotope and Noble Gas Isotope Composition and Distribution: A Case Study of Lower Silurian Longmaxi Shale Gas, Sichuan Basin

Cao

Yu-hu

et al. 2020

Energies

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The Weiyuan (WY) and Changning (CN) fields are the largest shale gas fields in the Sichuan Basin. Though the shale gases in both fields are sourced from the Longmaxi Formation, this study found notable differences between them in molecular composition, carbon isotopic composition, and noble gas abundance and isotopic composition. CO2 (av. 0.52%) and N2 (av. 0.94%) were higher in Weiyuan than in Changning by an average of 0.45% and 0.70%, respectively. The δ13C1 (−26.9% to −29.7%) and δ13C2 (−32.0% to −34.9%) ratios in the Changning shale gases were about 8% and 6% heavier than those in Weiyuan, respectively. Both shale gases had similar 3He/4He ratios but different 40Ar/36Ar ratios. These geochemical differences indicated complex geological conditions and shed light on the evolution of the Lonmaxi shale gas in the Sichuan Basin. In this study, we highlight the possible impacts on the geochemical characteristics of gas due to tectonic activity, thermal evolution, and migration. By combining previous gas geochemical data and the geological background of these natural gas fields, we concluded that four factors account for the differences in the Longmaxi Formation shale gas in the Sichuan Basin: a) A different ratio of oil cracking gas and kerogen cracking gas mixed in the closed system at the high over-mature stage. b) The Longmaxi shales in WY and CN have had differential geothermal histories, especially in terms of the effects from the Emeishan Large Igneous Province (LIP), which have led to the discrepancy in evolution of the shales in the two areas. c) The heterogeneity of the Lower Silurian Longmaxi shales is another important factor, according to the noble gas data. d) Although shale gas is generated in closed systems, natural gas loss throughout geological history cannot be avoided, which also accounts for gas geochemical differences. This research offers some useful information regarding the theory of shale gas generation and evolution.

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Pyrobitumen in South China: Organic petrology, chemical composition and geological significance

Cited by 35 publications

References 61 publications

Trace element characterization of bitumen constraints on the hydrocarbon source of the giant gas field in Sichuan Basin, South China

Trace element characterization of bitumen constraints on the hydrocarbon source of the giant gas field in Sichuan Basin, South China

A new genetic mechanism of natural gas accumulation

Factors Affecting Shale Gas Chemistry and Stable Isotope and Noble Gas Isotope Composition and Distribution: A Case Study of Lower Silurian Longmaxi Shale Gas, Sichuan Basin

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