Geochemical characteristics and mechanism of organic matter accumulation of marine-continental transitional shale of the lower permian Shanxi Formation, southeastern Ordos Basin, north China

Zhao, Bangsheng; Li, Rongxi; Wang, Ning; Zhou, Wei; Khaled, Ahmed; Zhao, Dong Liang; Zhang, Yanni; Wu, Xiaoli; Liu, Qi

doi:10.1016/j.petrol.2021.108815

Cited by 35 publications

(36 citation statements)

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“…Al and Ti are often used to represent terrigenous flux (Saito et al, 1992;Fu et al, 2015;Zhao et al, 2021). The SiO 2 of the samples has a weak negative correlation with Al 2 O 3 and TiO 2 (Figures 7A,B), indicating that terrigenous detrital quartz is not the main source of SiO 2 and there may be other sources of SiO 2 .…”

Section: Origin Of Silicamentioning

confidence: 99%

“…Paleoproductivity refers to the total amount of organic matter fixed per unit area per unit time (Algeo et al, 2011;Pan et al, 2020). Generally speaking, high organic productivity is one of the key factors for the formation of hydrocarbon source rocks (Talbot, 1988;Nelson et al, 1995;Mansour et al, 2020a;Mansour et al, 2020b;Yang et al, 2016;Zhao et al, 2021), and a large number of studies have shown that siliceous plankton in marine source rocks is the main provider of marine primary productivity (De Wever and Baudin, 1996;Chou et al, 2012;Xiang et al, 2013;Shaldybin et al, 2017;Jiang et al, 2019;Zhang et al, 2019), whose content is closely related to the biological reproduction in surface water, and its temporal and spatial distribution can be used to reflect the changing process of paleoproductivity. In recent years, many studies have shown that radiolarians enriched in marine hydrocarbon source rocks can gather together and absorb a lot of symbiotic algae in their bodies by using a large number of pseudopodia, forming a good symbiotic relationship with them (Lyle et al, 1988;Erbacher and Thurow, 1997;Xiang et al, 2013;Khan et al, 2019).…”

Section: Relationship Between Biogenic Silica and Organic Mattermentioning

confidence: 99%

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The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

Zhang

Huang

et al. 2021

Front. Earth Sci.

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The shale of the Wulalike Formation developed in the northwestern Ordos Basin is considered to be an effective marine hydrocarbon source rock. One of the key factors for successful shale gas exploration in the Wufeng–Longmaxi Formation in the Sichuan Basin is the high content of biogenic silica. However, few people have studied the siliceous origin of the Wulalike shale. In this study, we used petrographic observation and element geochemistry to analyze the origin of silica in the Wulalike shale. The results show that the siliceous minerals are not affected by hydrothermal silica and mainly consist of biogenic and detrital silica. A large number of siliceous organisms, such as sponge spicules, radiolarians, and algae, are found under the microscope. It has been demonstrated that total organic carbon has a positive correlation with biogenic silica and a negative correlation with detrital silica, and biogenic silica is one of the effective indicators of paleoproductivity. Therefore, the enrichment of organic matter may be related to paleoproductivity. Through the calculation of element logging data in well A, it is found that biogenic silica is mainly distributed in the bottom of the Wulalike Formation, and the content of biogenic silica decreases, while the content of detrital silica increases upward of the Wulalike Formation. Biogenic silica mainly exists in the form of microcrystalline quartz, which can form an interconnected rigid framework to improve the hardness and brittleness of shale. Meanwhile, biogenic microcrystalline quartz can protect organic pores from mechanical compaction. Therefore, it may be easier to fracture the shale gas at the bottom of the Wulalike Formation in well A.

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Section: Origin Of Silicamentioning

confidence: 99%

Section: Relationship Between Biogenic Silica and Organic Mattermentioning

confidence: 99%

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

Zhang

Huang

et al. 2021

Front. Earth Sci.

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“…Marine–continental transitional shales are mainly deposited in shallow water, such as shallow lake, epicontinental sea, delta, tidal flat, and lagoon environments. , Marine–continental transitional shales are widely distributed in the world, such as the Triassic Mungaroo shale in the Northern Carnarvon Basin of Australia; Cretaceous Gongila shale of in the Chad Basin of Nigeria; Permian Shanxi to Taiyuan shale in Ordos Basin of China; and the Permian Longtan shale in the Sichuan Basin of China. − Due to their considerable resource potential, the marine–continental transitional shale gas system is regarded as one of the hot topics of the academic and industrial community. ,,, Different from the marine shale, the formation of marine–continental transitional shale is influenced by marine and continental agents, which makes it very sensitive to climate and environmental changes, similar to the lacustrine shale. , Therefore, its sedimentary environment and lithology change frequently and have strong heterogeneity. Strong heterogeneity can be reflected in two dimensions.…”

Section: Introductionmentioning

confidence: 99%

Depositional Environment Variation and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shale in the Upper Permian Longtan Formation, Sichuan Basin, SW China

Wang

Guo

et al. 2022

ACS Earth Space Chem.

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Marine−continental transitional shale gas exploration is one of the hottest topics in the academic and industrial community. Frequent sedimentary environment changes lead to substantial heterogeneity and complex organic matter enrichment mechanisms, and it is of great practical significance to clarify the paleoenvironment of marine−continental transitional shale and reveal the enrichment mechanism of organic matter for subsequent shale gas exploration. However, strong heterogeneity creates divergence for our understanding of organic matter enrichment mechanisms and resource potential. This paper selected the marine−continental transitional shale of the Permian Longtan Formation in the southeastern Sichuan Basin as an example. Through TOC analysis, XRD measurements, and major and trace element analyses, we identify the depositional cycle and lithofacies, characterize the paleosedimentary environments of different lithofacies, establish depositional models, and clarify the organic matter enrichment mechanism. Four lithofacies can be identified in the Longtan Formation in the study area: organic−lean carbonate shale (LC), organic−lean mixed shale (LM), organic−lean argillaceous shale (LCM), and organic−rich argillaceous shale (RCM). The terrestrial detrital influx of the LCM and RCM shales is obviously strong, while the RCM shale was deposited in a relatively dysoxic and humid environment. For the Longtan shale, the terrestrial detrital influx and redox environment determine the enrichment of organic matter. In the lagoon sediment system, due to the high terrestrial detrital influx, the argillaceous shale in the transitional shale gas system should be given more attention in future exploration. For different kinds of shale gas systems (marine, marine− continental transitional, and lacustrine), the effect of the terrestrial detrital influx is the main difference. In marine−continental and lacustrine shale gas systems, shales with high TOC values can still exist in the context of oxic sedimentary environments. The research results of this paper can provide a theoretical basis for future marine−continental transitional shale gas sweet spot prediction and exploration from geochemical perspectives.

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“… 7 The previous studies on the transitional shale mainly focused on resource potential evaluation and pore structure characterization, but the pore origin was rarely studied. 6 − 10 The transitional shale reservoir which is located in Shanxi Formation, eastern Ordos Basin, is characterized by wide distribution, large cumulative thickness, and high organic matter (OM) content, showing good prospects for gas exploration and development. 7 , 10 − 12 With the increasing understanding of shale gas resources, researchers have found that the proportion of adsorbed gas in the shale is 20–85%, and the smaller the pores, the higher the adsorption capacity of methane, due to their large specific surface area (SSA).…”

Section: Introductionmentioning

confidence: 99%

“… 6 − 10 The transitional shale reservoir which is located in Shanxi Formation, eastern Ordos Basin, is characterized by wide distribution, large cumulative thickness, and high organic matter (OM) content, showing good prospects for gas exploration and development. 7 , 10 − 12 With the increasing understanding of shale gas resources, researchers have found that the proportion of adsorbed gas in the shale is 20–85%, and the smaller the pores, the higher the adsorption capacity of methane, due to their large specific surface area (SSA). 13 − 15 Moreover, the adsorption capacity of organic pores and inorganic mineral pores in the shale matrix also shows a big difference.…”

Section: Introductionmentioning

confidence: 99%

Nanopore Structure and Origin of Lower Permian Transitional Shale, Eastern Ordos Basin, China

et al. 2022

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Nanopores in the shale play a vital role in methane adsorption, and their structural characteristics and origins are of great significance for revealing the mechanism of methane adsorption, desorption, and diffusion. In this paper, through low-temperature ashing and low-pressure gas adsorption experiments, the nanopore structure of original shales and ashed shales was quantitatively characterized, and the nanopore origins in the transitional shale of lower Permian in eastern Ordos Basin were analyzed. The results show that the pore volume (PV) and specific surface area (SSA) of nanopores in transitional shale reservoirs are 0.0217–0.0449 cm 3 /g and 13.91–51.20 m 2 /g, respectively. The average contribution rates of micropores (<2 nm), mesopores (2–50 nm), and macropores (50–100 nm) to PV are 18.78, 72.26, and 8.96%, respectively, and the average contribution rates to SSA are 66.19, 33.10, and 0.71%, respectively. In addition, it is found that the average contribution rates of inorganic minerals and organic matter to the SSA of micropores are 55.9 and 44.1%, respectively, and the average contribution rates to the SSA of mesopores are 92.3 and 7.7%, respectively. Combining the adsorption properties of the main clay minerals and kerogen in shale, it is concluded that organic pores control the adsorption of methane with an absolute advantage in transitional shales. It is of great significance to understand the mechanism of methane occurrence, desorption, and diffusion in shales by clarifying the origins of multiscale pores.

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Geochemical characteristics and mechanism of organic matter accumulation of marine-continental transitional shale of the lower permian Shanxi Formation, southeastern Ordos Basin, north China

Cited by 35 publications

References 58 publications

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

Depositional Environment Variation and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shale in the Upper Permian Longtan Formation, Sichuan Basin, SW China

Nanopore Structure and Origin of Lower Permian Transitional Shale, Eastern Ordos Basin, China

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