Organic matter provenance and depositional environment of marine-to-continental mudstones and coals in eastern Ordos Basin, China—Evidence from molecular geochemistry and petrology

Qi, Yu; Ju, Yi‐Hsu; Tan, Jingqiang; Bowen, Leon; Yu, Kun; Zhu, Hongtao; Huang, Cheng; Zhang, Weilai

doi:10.1016/j.coal.2019.103345

Cited by 33 publications

(14 citation statements)

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“…However, the accumulation of organic matter always depends on the paleoenvironment and paleoclimate in the sedimentary period . The anoxic water environment and stable provenance are favorable for the preservation of organic matter. , Compared with the marine shale, the organic matter in transitional source rocks is possibly derived from both marine and terrestrial inputs. , This difference in source inputs also indirectly leads to the uniqueness of transitional gas generation, accumulation, and storage. Meanwhile, the difference of carbon and nitrogen stable isotopes between natural gas and organic matter is an important symbol to distinguish marine source rocks from transitional source rocks. , On the other hand, transitional strata are usually the assemblage of coal, mudstone, shale, and sandstone and form a cyclical distribution of lithology vertically. , This also leads to the special diagenetic background of transitional facies, making the mineral and maceral composition of coal-bearing rocks influenced by the terrigenous clastic material compared with marine shale. − Moreover, burial thermal metamorphism experienced by transitional source rocks in North China is weaker than that of marine shale, which leads to the lower maturity of organic matter. − Accordingly, the thermal evolution and hydrocarbon generation potential of transitional shale are very different from those of marine shale.…”

Section: Introductionmentioning

confidence: 99%

“…12,21 Compared with the marine shale, the organic matter in transitional source rocks is possibly derived from both marine and terrestrial inputs. 22,23 This difference in source inputs also indirectly leads to the uniqueness of transitional gas generation, accumulation, and storage. Meanwhile, the difference of carbon and nitrogen stable isotopes between natural gas and organic matter is an important symbol to distinguish marine source rocks from transitional source rocks.…”

Section: Introductionmentioning

confidence: 99%

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Paleoenvironment, Provenance, and Hydrocarbon Potential of Lower Permian Coal-Bearing Source Rocks in the Southern North China Basin: A Case Study of the Pingdingshan Coalfield

Wan

et al. 2022

ACS Earth Space Chem.

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Coal measures, widely developed in the marine–continental transitional environment, have been regarded as an important reservoir of petroleum resources, such as coalbed methane, shale gas, and tight sandstone gas. In this study, petrography, organic geochemistry, and isotope geochemistry were conducted to reveal the organic matter sources, maturation, and paleoenvironment of Permian coal-bearing source rocks in the Pingdingshan coalfield, China. Organic petrography indicates that the organic matter of the Lower Shanxi shales are derived from the terrigenous and marine mixed inputs and those of the coals are mostly sourced from terrigenous input. Thermal parameters suggest that the source rocks of the Lower Shanxi Formation reached the late oil generation stage (∼1.06% R o), and that of the Upper Shanxi Formation entered the early oil generation stage (∼0.87% R o). Geochemical results suggest good hydrocarbon potential of all coal samples but poor potential of most mudstones and shales. The generated hydrocarbons generally originate from the in situ source rocks, and no obvious migrated hydrocarbons exist due to the low production indexes. δ13C and δ15N values of coals are significantly more negative than those of mudstones and shales, suggesting that the plants flourished with efficient photosynthesis and the coals experienced intense microbial nitrogen fixation during the coal-forming period. Rapid propagation of terrestrial plants leads to the increase of carbon fixation by photosynthesis and the enrichment of 13C in the atmosphere. The increase of the sea level may lead to the massive burial of terrestrial plants in peat swamps, which decreases the photosynthesis and increases nitrogen fixation, resulting in the depletion of 13C in the atmosphere and the enrichment of 15N in organic matter.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Paleoenvironment, Provenance, and Hydrocarbon Potential of Lower Permian Coal-Bearing Source Rocks in the Southern North China Basin: A Case Study of the Pingdingshan Coalfield

Wan

et al. 2022

ACS Earth Space Chem.

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“…Previous studies on the coal seams of the Shanxi and Taiyuan Fms. in the southern Ordos Basin mostly focused on the geochemical characteristics of the coal seams [12][13][14][15]. Due to the limited data, their vertical and lateral distributions were not very clear.…”

Section: Introductionmentioning

confidence: 99%

Distribution of Upper Paleozoic Coal Seams in the Southeastern Ordos Basin

Guan

Guo

et al. 2022

Energies

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The Ordos Basin contains abundant coal resources in the Upper Paleozoic strata. They are shallowly buried or exposed in the periphery of the basin, forming recoverable coal mines and coalbed methane resources. For the deeply buried coal seams of the basin, however, due to complex changes and difficult mining, less attention was paid before. In recent years, with the exploitation of tight gas related to coal source rocks, a large amount of drilling and seismic data has been accumulated in the southeastern Ordos Basin, which makes it possible to study the distribution change and factors controlling Upper Paleozoic coal seams. Delineation of deep coal development and distribution is an important basis for coal, coalbed methane and related tight gas resources in the Upper Paleozoic. We use core, logging and seismic data to analyze the coal geophysics, thickness variation, paleotopography and sedimentary facies in the southeastern Ordos Basin. The lower part of the Shanxi Formation (Fm.) and the upper part of the Taiyuan Fm. in the southeastern part of the basin are characterized by low natural gamma ray, low density, high resistivity and high sonic logging values. As the coal velocity is very low and alternates with the high-velocity Taiyuan Fm. and Ordovician limestones, the two sets of coals below and above the Taiyuan limestones form an extremely strong-amplitude reflection in the seismic profile. The two sets of coals are cumulatively 1–10 m thick, averaging 2.4 m, and 4 m is the maximum induvial thickness. The individual coal seams thicker than 2 m cover an area of approximately 2500 km2, and the burial depths of the coal seam range from 2500 to 3000 m. The thick coal seams of the Taiyuan Fm. are mainly distributed proximally in the Ordovician paleokarst depression, while the Ordovician paleokarst depression without incised origin was deposited by distal coeval limestone rocks. There is a complementary relationship between the coal seams and the thickened zone of distributary channel sandstone in the Shanxi Fm.

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“…Transitional shales are commonly small in thickness and are interbedded with tight sandstone, limestone, and coal, resulting in a unique pore structure (Gentzis, 2013;Yang et al, 2017;Qi et al, 2020). Marine-continental transitional sedimentary facies can be divided into various sub-facies (Galloway, 1998;Boggs, 2012;Harraz, 2013).…”

Section: Introductionmentioning

confidence: 99%

Mineralogy and Pore Structure of Marine–Continental Transitional Shale: A Case Study of the Upper Carboniferous Keluke Formation in the Eastern Qaidam Basin, China

Guo

Fang

Wang³

et al. 2022

Front. Earth Sci.

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Organic-rich shale and associated fine-grained sedimentary rocks of marine-continental transitional facies were well developed in the Upper Carboniferous Keluke Formation in the Eastern Qaidam Basin, which is expected to be a set of potential shale gas exploration and development target. Mineralogy and pore structure of marine-continental transitional shale were investigated systematically based on thin-section identification, X-ray diffraction (XRD), helium porosity test and pressure-pulse permeability measurement, scanning electron microscopy (QEMSCAN), field emission scanning electron microscopy (FESEM), and high-pressure mercury injection (MICP) and nitrogen adsorption. Thin section, XRD, and QEMSCAN data suggest that marine–continental transitional shale has complex mineral compositions, resulting in mixed rocks and mixed sequences. FE-SEM images show that interparticle and intercrystalline pores are popular in the Keluke Shales, with minor dissolution pores and microfractures. No secondary organic matter pores occur in the Keluke Shales because organic macerals are dominated by vitrinite and inertinite, where only primary pores can be found among organic matter frameworks. MICP and nitrogen adsorption indicate that pore size distributions follow a bimodal pattern and proportions of micro-scale pores and macro-scale pores increase in an order: bioclastic limestone, argillaceous bioclastic limestone, silty mudstone, argillaceous siltstone. The differences in pore structure are caused by sedimentary facies and associated mineralogy and diagenesis. This study can provide a crucial theoretical guidance for sweet spots determination and deep understanding of transitional shale gas potential.

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Organic matter provenance and depositional environment of marine-to-continental mudstones and coals in eastern Ordos Basin, China—Evidence from molecular geochemistry and petrology

Cited by 33 publications

References 106 publications

Paleoenvironment, Provenance, and Hydrocarbon Potential of Lower Permian Coal-Bearing Source Rocks in the Southern North China Basin: A Case Study of the Pingdingshan Coalfield

Paleoenvironment, Provenance, and Hydrocarbon Potential of Lower Permian Coal-Bearing Source Rocks in the Southern North China Basin: A Case Study of the Pingdingshan Coalfield

Distribution of Upper Paleozoic Coal Seams in the Southeastern Ordos Basin

Mineralogy and Pore Structure of Marine–Continental Transitional Shale: A Case Study of the Upper Carboniferous Keluke Formation in the Eastern Qaidam Basin, China

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