Differential enrichment mechanism of organic matters in the marine-continental transitional shale in northeastern Ordos Basin, China: Control of sedimentary environments

Chen, Yuhang; Wang, Yingbin; Guo, Mingqiang; Wu, Heyuan; Li, Jun; Wu, Wenzhuo; Zhao, Junping

doi:10.1016/j.jngse.2020.103625

Cited by 46 publications

(39 citation statements)

References 80 publications

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“…Previous studies have shown that the R o of marine shales in southern China is generally greater than 2% due to deep burial experience, which is characterized by high maturity of OM and large amount of gas generation, while the R o of shales in the study area generally ranges from 0.9 to 1.7%, which is characterized by low maturity and small amount of gas generation. 1 In addition, the difference may be caused by different hydrocarbon generation patterns between type III kerogen and type I/II kerogen developed in shales. 4 , 49 , 50 The development of inorganic nanopores in minerals cannot be ignored.…”

Section: Resultsmentioning

confidence: 99%

“…In recent years, with the industrial development of marine shale gas in North America and southern China, researchers have been attracted to study the exploration potential of marine-continental transitional shale gas. 1 − 6 China’s transitional shale gas resources amount to 19.8 trillion cubic meters, accounting for 25% of the total shale gas resources. 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.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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“…The mobility of Sr in water and the solubility product of its sulfate compounds are higher than those of Ba. Therefore, the Sr/Ba ratio can also effectively reflect the salinity variation of water bodies (Chen et al, 2020;Wang, He, Zhu, & Ding, 2020); however, the effect of carbonate-hosted Sr needs to be excluded (Remírez & Algeo, 2020).…”

Section: Sedimentary Environmentmentioning

confidence: 99%

Geochemical characteristics and the significance of two major coal‐bearing strata claystones from the Datong Coalfield (North China)

Liu

Zhang

et al. 2022

Geological Journal

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This study aims to investigate the significance of the geochemical differences and the factors that control the geochemistry of two major types of coal‐bearing stratum claystones (sedimentary kaolinitic claystone [SK‐claystone] and tonstein). The SK‐claystone and tonstein derived from the Taiyuan Formation of the Upper Carboniferous coal‐bearing strata in the Datong Coalfield of North China have been comprehensively analysed using X‐ray powder diffractometer, scanning electron microscopy, X‐ray fluorescence, and inductively coupled plasma mass spectrometry. The results showed that the SK‐claystones and tonsteins exhibit similar SiO2 content; however, the content of Al2O3 in tonsteins is higher than that in SK‐claystones, whereas the TFe2O3 and K2O content in tonsteins are lower than those in SK‐claystones. These findings are consistent with the mineral composition analysis of the samples. The SK‐claystones and tonsteins have different parent rocks, as shown by the Al2O3/TiO2 ratios, diagram of Zr/TiO2 versus Nb/Y, and chondrite‐normalized rare earth element patterns. The palaeosalinity indexes (B/Ga and Sr/Ba) and palaeoredox proxies (Mo and U enrichment factors as well as U/Th ratios) indicate that both SK‐claystones and tonsteins were formed in freshwater suboxic–oxic environments. The kaolinite in SK‐claystones and tonsteins is formed via the deposition or crystallization of aluminium‐rich weathering products and alteration of volcanic ash, respectively. In summary, the different parent rocks and diagenetic processes are the main factors differentiating the geochemical characteristics of the two types of claystones. Our study links the different types of elemental enrichment features to the geological genesis of the two types of claystones, indicating that the trace elemental enrichment characteristics can be used as indicators for distinguishing the SK‐claystone and tonstein in the Datong Coalfield as well as other similar coalfields.

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“…The Ordos Basin can further be divided into six different units (Yimeng Uplift, Western Fold and Thrust Belt, Tianhuan Depression, Shanbei Slope, Jinxi Flexural Fold Belt, and Weibei Uplift) [41,42] (Figure 1). A thick sequence of carbonate rocks was deposited in the marine settings from Proterozoic-Lower Paleozoic time [25,43]. The Carboniferous to Permian system is a distinctive marinecontinental transitional system that results in the deposition of interbedded shale, sandstones, coal, and carbonate rocks in the Upper Carboniferous Benxi Formation, the Lower Permian Taiyuan Formation, and the Shanxi Formation in the Ordos Basin [44][45][46] (Figure 2).…”

Section: Geological Backgroundmentioning

confidence: 99%

Reservoir Characteristics of the Lower Permian Marine-Continental Transitional Shales: Example from the Shanxi Formation and Taiyuan Formation in the Ordos Basin

et al. 2021

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The pore types and pore structure parameters of the heterogenetic shale will affect the percolation and reservoir properties of shale; therefore, the research on these parameters is very important for shale reservoir evaluation. We used X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), low-pressure CO2 adsorption analysis, mercury injection capillary pressure (MICP), and high-pressure methane adsorption analysis to analyze the characteristics of different pore types and their parameters of the Lower Permian Shanxi Formation and Taiyuan Formation in the Ordos Basin. The influence of different mineral contents on the porosity and pore size is also investigated. The Shanxi Formation (SF) is composed of quartz (average of 38.4%), plagioclase, siderite, Fe-dolomite, calcite, pyrite, and clay minerals (average of 50.1%), while the Taiyuan Formation (TF) is composed of calcite (average of 37%), siderite, Fe-dolomite, quartz, pyrite, and clay minerals (average of 32.3%). The most common types of pores observed in this formation are interparticle pores (InterP pores), intraparticle pores (IntraP pores), interclay pores, intercrystalline pores (InterC pores), organic matter pores (OM pores), and microfractures. CO2 adsorption analysis demonstrates the type I physisorption isotherms, showing microporous solids having comparatively small external surfaces. The similar types of isothermal shapes of the Shanxi Formation (SF) and Taiyuan Formation (TF) suggest that both types have similar pore size distribution (PSD) within the measured pore range by the low-pressure CO2 adsorption experiment. The micropore pore size of the TF is larger than that of the SF. MICP shows the larger pores (>50 nm), and most of the volume was adsorbed by macropores. Methane gas sorption capacity increases with increasing pressure. Clay minerals and quartz played an important role in providing adsorption sites for methane gas. The overall analysis of both formations shows that TF has good reservoir properties than SF.

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Differential enrichment mechanism of organic matters in the marine-continental transitional shale in northeastern Ordos Basin, China: Control of sedimentary environments

Cited by 46 publications

References 80 publications

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

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

Geochemical characteristics and the significance of two major coal‐bearing strata claystones from the Datong Coalfield (North China)

Reservoir Characteristics of the Lower Permian Marine-Continental Transitional Shales: Example from the Shanxi Formation and Taiyuan Formation in the Ordos Basin

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