Sedimentary environment and organic enrichment mechanisms of lacustrine shale: A case study of the Paleogene Shahejie Formation, Qikou Sag, Bohai Bay Basin

Wu, Zhuoya; Zhao, Xianzheng; Wang, Enze; Pu, Xipeng; Lash, Gary G.; Han, Wenzhong; Zhang, Wei; Yuan, Feng

doi:10.1016/j.palaeo.2021.110404

Cited by 30 publications

(42 citation statements)

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“…For reconstructing paleoclimatic characteristics, Zhao et al , used the principle that different elements tend to be enriched in sediments under various climatic conditions, for example, Fe, Mn, and Cr are mainly enriched in humid environments, while Ca, Mg, and Sr are mainly enriched in arid conditions, proposing the C –value for the quantitative characterization of the paleoclimate. This value is widely used in paleoclimate condition reconstruction, ,, and the calculation method is shown in eq . where Fe, Mn, Cr, Ni, V, Co, Ca, Mg, Sr, Ba, K, and Na are the elemental contents in sediment (ppm). In general, C –values less than 0.2, from 0.2 to 0.4, 0.4 to 0.6, 0.6 to 0.8, and greater than 0.8 represent arid, semiarid, semiarid to semihumid, semihumid, and humid paleodepositional environments, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, we need more research to deepen our understanding about the organic matter enrichment mechanisms of marine–continental transitional shale to better guide the exploration and development of shale gas. At present, the geochemical proxies are the most commonly used methods to reconstruct the paleoenvironments. − For example, due to different solubilities of various redox conditions, the contents and ratios of redox–sensitive elements can be used to evaluate the redox conditions. , The Al and Ti are rarely affected in the diagenesis process, and their content can characterize the input of terrigenous debris . Based on these parameters, we can reconstruct the paleoenvironment and clarify the organic matter enrichments.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Methodsmentioning

confidence: 99%

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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“…Macroseepage are the large visible concentration of hydrocarbons on the surface, which can be considered as a direct hydrocarbon indicator (DHI) and the micro seepages are not visible, but can be noticed in the form of stains and odors. Seeped gases can migrate vertically as well as laterally via porous, permeable damage zones of faults, fractures or vents causing chemical changes in the soil 2 , 6 – 12 . Hydrocarbons flows within the reservoir rocks due to buoyancy force, while it can migrate from the source to the reservoir through capillary imbibition 13 – 15 .…”

Section: Introductionmentioning

confidence: 99%

Macro-seepage based potential new hydrocarbon prospects in Assam-Arakan Basin, India

Boruah

Verma

Rasheed

et al. 2022

Sci Rep

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Active macro seepages of methane that occur in between the north bank of the Brahmaputra river and Himalayan foothill region of Assam Arakan Basin, India, indicate the presence of hydrocarbon accumulation in the subsurface, but the hydrocarbon prospects in this region are not well studied. We carried out an extensive field sampling, which included a total of 58 sediment core collections from an active gas seepage location and nearby areas at a depth of 2–2.5 m. Our sample locations are placed at 1 km intervals laterally. We performed laboratory investigations and mapped near-surface chemical alterations associated with active macro seepages and microseepages. The analysis of geochemical composition of hydrocarbon gases in the sediment indicates both the biogenic and thermogenic origins of seeped hydrocarbons. The stable isotope analysis of methane suggests the presence of thermogenic as well as mixed biogenic-thermogenic gases. The presence of such mixing of gases is caused by the secondary alteration processes during their migration through potential faults and fractures. The trace elements of the sediments show anomalous concentrations at different parts of the study area, with a wide range of concentrations for Ba (54 to 492 ppm), Cu (1–25 ppm), Cr (61–329 ppm), Ni (1–42 ppm), Pb (2–48 ppm), Th (2–32 ppm), U (4–39 ppm), V (19–133 ppm) and U (0.87–6.5 ppm). There are higher concentrations of adsorbed gases, trace elements, and microbes along the identified lineaments. Such higher concentration can be triggered by high hydrocarbon-oxidizing bacteria count, which is greater than 104 cfu/gm of soil of bacterial growth around the lineaments. We identified potential hydrocarbon prospects based on the macro and micro seepage analysis using integrated geological, geochemical and microbial techniques in the study area.

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“… 9 − 11 The bivariate diagrams of Al 2 O 3 /(Al 2 O 3 + Fe 2 O 3 )–Fe 2 O 3 /TiO 2 and Al 2 O 3 /(Al 2 O 3 + Fe 2 O 3 )–La N /Ce N (subscript N indicates PAAS standardization) are commonly used to judge the tectonic setting of parent rocks. 12 The proxies of the chemical index of alteration (CIA), Sr/Cu and Rb/Sr, are usually used to evaluate the paleoclimate, 10 , 13 and the proxy of the Sr/Ba ratio is widely used to evaluate seawater salinities. 14 − 16 Some redox-sensitive elements such as V, Cr, Ni, Co, Th, U, and Mo in sedimentary rocks are usually used to indicate redox characteristics due to their differentiation under various conditions, and the ratios of U/Th, V/Cr, and Ni/Co are common proxies for judging paleoredox conditions.…”

Section: Introductionmentioning

confidence: 99%

Paleoenvironment Evolutionary Characteristics of Niutitang Shale in Western Hubei, Middle Yangtze, China

Huang

Liu

et al. 2022

ACS Omega

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The black shale developed in the first section of the Niutitang formation (ϵ 1 n 1 ) is one of the most important shale gas reservoirs in western Hubei, and its geological characteristics have been sufficiently studied by many predecessors. However, there are still three aspects that need further research: the origin of silicon, the discrimination of the euxinic sulfuretted and the anoxic ferruginous conditions, and the main controlling factors of organic matter enrichment. Based on geochemical data from well ZD1 located in the city of Yichang in western Hubei, first, the geochemical characteristics of ϵ 1 n 1 are analyzed, then the provenance, depositional site, and paleoenvironment evolution are discussed, and finally, the main controlling factor of organic matter enrichment is revealed. The results show that ϵ 1 n 1 can be divided into two units, organic-rich shales (ORS) and organic-lean shales (OLS), which have average total organic carbon contents of 4.21 and 0.84%, respectively. Additionally, the ORS is characterized by high contents of SiO 2 , U, V, Ni, Zn, and Cu and left-inclining types of rare earth element distribution curves. ϵ 1 n 1 is located in a passive continental margin with a material source mainly from mixed felsic and mafic rocks. Compared with the OLS, the content of biological quartz is much greater, and the terrigenous input is less in the ORS. The paleoclimate is cold and humid with low salinity in the ORS, whereas it is hot and dry with high salinity in the OLS. ϵ 1 n 1 is deposited in a semistagnant basin, and the ORS shows a relatively lower stagnant degree with euxinic to anoxic conditions and moderate to high paleoproductivity, while the OLS shows a high stagnant degree with suboxic to oxic conditions and lower paleoproductivity. The redox conditions are the main controlling factors affecting organic matter enrichment. The environmental evolution model with three stages shows that there is a good causal relationship between redox conditions, paleoproductivity, and sea level fluctuation. The black carbonaceous siliceous in the lower part of the ORS with a thickness of approximately 40 m is the most favorable layer, which will provide a theoretical basis for further shale gas exploration of ϵ 1 n 1 in the western Hubei.

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Sedimentary environment and organic enrichment mechanisms of lacustrine shale: A case study of the Paleogene Shahejie Formation, Qikou Sag, Bohai Bay Basin

Cited by 30 publications

References 102 publications

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

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

Macro-seepage based potential new hydrocarbon prospects in Assam-Arakan Basin, India

Paleoenvironment Evolutionary Characteristics of Niutitang Shale in Western Hubei, Middle Yangtze, China

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