Geochemical characteristics of Longmaxi Formation shale gas in the Weiyuan area, Sichuan Basin, China

Feng, Ziqi; Dong, Dazhong; Tian, Jinqiang; Qiu, Zhen; Wu, Wei; Zhang, Cong

doi:10.1016/j.petrol.2018.04.030

Cited by 40 publications

(26 citation statements)

References 35 publications

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“…According to the lithology and graptolite zone variation characteristics, the gas-bearing interval of the Longmaxi Formation is subdivided into four layers including LM 1-1-1, LM 1-1-2, LM 1-1-3, and LM 1-1-4, respectively ( Figure 2). In this article, we mainly concentrate upon the first member of the Longmaxi Formation (LM 1-1; Feng et al, 2018).…”

Section: Geological Settingsmentioning

confidence: 99%

Palaeoenvironmental analysis of the Lower Silurian Longmaxi Formation in the Zhaotong area of the Sichuan Basin, South China: Implications for organic matter accumulation mechanisms

Zhou

Liu

et al. 2020

Geological Journal

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Geochemical data have been used as the most effective proxies for determining palaeoclimate and palaeoenvironmental conditions. In this article, we conduct a systematic review on a variety of geochemical data of sediments that are considered proxies for tracing palaeoclimate and palaeoenvironmental information. Comprehensive studies have been carried out on the palaeoproductivity, redox conditions, palaeoclimate, and the acquired data on the enrichment mechanism of organic matter have been summarized. The general mechanisms of the geochemical data regarded as the palaeoclimate and palaeoenvironmental archives include the characteristics of mineral composition, major and trace elements, and rare earth elements. The palaeoproductivity index, including the Ba and P, indicate that the organic‐rich shale was deposited in a high‐productivity water column. The trace elements revealed that the Longmaxi units recorded variable redox conditions from anoxic to aerobic. The elements V, U, Th, Ni, and Co together with the U/Th, V/Cr, Ni/Co, and V/(V + Ni) are essential indicators for defining the redox conditions. The NASC‐normalized REE + Y distribution indicates that the Longmaxi Formation was slightly altered by detrital materials in reduced and acidic environments. The Sr/Cu and MgO/CaO all reveal that the palaeoclimate was gradually transformed from humid to dry heat. The Sr/Ba ratio implies that the water depth fluctuates frequently at the early stage of sedimentation. All geochemical data integrated with the sedimentary characteristics show that anoxic conditions, high palaeoproductivity, and relatively humid palaeoclimates contributed to the accumulation of organic‐rich shale. We propose that jointly utilizing various geochemical and sedimentary indices can expand the outlook of the palaeoenvironment and provide a better understanding of the organic matter accumulation mechanisms.

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Section: Geological Settingsmentioning

confidence: 99%

Palaeoenvironmental analysis of the Lower Silurian Longmaxi Formation in the Zhaotong area of the Sichuan Basin, South China: Implications for organic matter accumulation mechanisms

Zhou

Liu

et al. 2020

Geological Journal

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“…Even if these shale gases come from the same area and same strata, variations in molecular composition, carbon isotopic composition, and noble gas abundance and isotopic composition can be found [15,16]. Recently, we found that the gas geochemical characteristics of shale gases from the Longmaxi Formation, Sichuan Basin, China, show several apparent differences between the Weiyuan (WY) and Changning (CN) areas [14][15][16][17][21][22][23]. For instance, there is more CH 4 in CN shale gas, and its carbon isotope composition is heavier than that of WY shale gas [14,16,17,[21][22][23].…”

Section: Introductionmentioning

confidence: 98%

“…Recently, we found that the gas geochemical characteristics of shale gases from the Longmaxi Formation, Sichuan Basin, China, show several apparent differences between the Weiyuan (WY) and Changning (CN) areas [14][15][16][17][21][22][23]. For instance, there is more CH 4 in CN shale gas, and its carbon isotope composition is heavier than that of WY shale gas [14,16,17,[21][22][23]. Meanwhile, the He and Ar abundance and isotope composition are higher in WY shale gas than in CN shale gas [15].…”

Section: Introductionmentioning

confidence: 99%

“…We collected and compared the geochemical data from our previous works [14][15][16] and other studies [16,21,22] and combined the geological background and oil/gas generation theory to clarify the causes and mechanics of variations in the geochemical characteristics of shale gas from the Longmaxi Formation, Sichuan Basin, China. These results should increase our understanding of the generation and evolution of shale gas.…”

Section: Introductionmentioning

confidence: 99%

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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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“…According to the Chinese Ministry of Land Resources, shale gas recoverable resources in China exceed 31 × 10 12 m 3 (Chinese Ministry of Land Resources, ). Five key shale gas demonstrations including Weiyuan, Changning, Fushun‐Yongchuan, Zhaotong, and Fuling areas were determined by the National Energy Board in 2017 (Feng et al, ). The shale gas production of China was 90 × 10 8 m 3 in 2017, which was ~6% of total gas production.…”

Section: Introductionmentioning

confidence: 99%

Mineralogy and geochemical investigation of Cambrian and Ordovician–Silurian shales in South China: Implication for potential environment pollutions

et al. 2019

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Rapid expansion of shale gas development in China raises environmental and human health concerns. Several studies present related information on these concerns in the United States and Canada, yet they are few in China at present. This paper presents a series of original and published mineralogical and trace elements data from two gas shales (Niutitang shale and Longmaxi shale) considered as producing gas shale in China. Mineralogical and geochemical data surveyed can be applied to evaluate the potential environment pollutions during shale weathering and hydraulic fracturing. After compilations of the mineralogical and trace elements data, we can conclude that (a) there is generally more pyrite compared with carbonate for Niutitang shales, indicating that Niutitang shales are more prone to generate the hydrogen ions than Longmaxi shales; (b) many of the environmental hazardous trace elements considered here show an association with organic matter and/or pyrite, indicating that these trace elements are prone to mobilize and release during shale weathering and hydraulic fracturing; (c) some environmental hazardous elements like As, Ni, and Ba that have extremely high concentrations in some regions as compared with the screening limits for soil and drinking water should attract more attention; and (d) clay-rich shale with abundant organic matter may be the most favourable shale gas reservoir for the Niutitang shale, especially for those shales in Lower Yangtze region. Moreover, more mineralogical and geochemical data will be required for a comprehensive environmental impacts assessment. KEYWORDS environmental and human impacts, mineralogy, pyrite oxidization, shale, South China, trace elements

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Geochemical characteristics of Longmaxi Formation shale gas in the Weiyuan area, Sichuan Basin, China

Cited by 40 publications

References 35 publications

Palaeoenvironmental analysis of the Lower Silurian Longmaxi Formation in the Zhaotong area of the Sichuan Basin, South China: Implications for organic matter accumulation mechanisms

Palaeoenvironmental analysis of the Lower Silurian Longmaxi Formation in the Zhaotong area of the Sichuan Basin, South China: Implications for organic matter accumulation mechanisms

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

Mineralogy and geochemical investigation of Cambrian and Ordovician–Silurian shales in South China: Implication for potential environment pollutions

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