Quartz types, origins and organic matter-hosted pore systems in the lower cambrian Niutitang Formation, middle yangtze platform, China

Abstract The lower Cambrian Niutitang shales, as one of target intervals with the greatest potential for shale gas exploration and development, have attracted much attention. Nevertheless, the organic matter enrichment mechanisms of the lower Cambrian Niutitang shales need further study, especially in the hydrothermal active zone. In this study, samples from ND1 well in western Hubei Province, middle Yangtze region, South China, were investigated for the controlling factors of organic matter accumulation of Lower Cambrian Niutitang shales by detailed petrographic, mineralogic, and geochemical proxies. The results show that hydrothermal activity and sea level fluctuation controlled the redox conditions and paleoproductivity of seawater and ultimately controlled the organic matter accumulation of Niutitang formation. In the Niu-1 member, the intense hydrothermal events lead to a suboxic to anoxic environment, which is conducive to the organic matter preservation. However, low sea level strengthens the restriction of water mass and reduced nutrient upwelling into the shelf, leading to decreased marine primary productivity, which was ultimately responsible for depleted organic matter accumulation in the Niu-1 member. In the Niu-2 member, the anoxic-euxinic environment and high paleoproductivity, driven by continuous hydrothermal activity and rising sea level, were the main factors controlling the enrichment of organic matter. In the Niu-3 member, the dysoxic to oxic condition plus low primary productivity, caused by the disappearance of hydrothermal activities and sea-level fall, resulted in the unfavorable organic matter accumulation. The results of this paper enrich the model of organic matter enrichment in the lower Cambrian black shale in the middle Yangtze region.

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Analysis of Gas Composition and Nitrogen Sources of Shale Gas Reservoir under Strong Tectonic Events: Evidence from the Complex Tectonic Area in the Yangtze Plate

Energies ◽

10.3390/en13010281 ◽

2020 ◽

Vol 13 (1) ◽

pp. 281 ◽

Cited By ~ 1

Author(s):

Xin Wang ◽

Zhenxue Jiang ◽

Kun Zhang ◽

Ming Wen ◽

Zixin Xue ◽

...

Keyword(s):

Organic Matter ◽

Shale Gas ◽

Lower Cambrian ◽

Thermal Evolution ◽

Ion Beam ◽

Nitrogen Sources ◽

Hydrocarbon Generation ◽

Thrust Faults ◽

Yangtze Platform ◽

Shale Reservoir

Strong tectonic movement brings great risk to exploration of shale gas in southern China, especially in Lower Cambrian shale with complex tectonic backgrounds, which has good hydrocarbon-generation matter but low or no gas content. In this paper, the Lower Cambrian shale from the southeast Chongqing region, located in the Upper Yangtze Platform, and the Xiuwu Basin, located in the Lower Yangtze Platform, were selected as the research objects. First, the gas components in shale gas samples were measured, then analysis of nitrogen isotopic was used to reveal the nitrogen sources. Using regional geological backgrounds, core description, and seismic interpretation, combined with the perpendicular and parallel permeability test and focused ion beam–helium ion microscopy (FIB–HIM) observation, the reasons for high content of nitrogen in the Lower Cambrian shale from the Xiuwu Basin and the Southeast Chongqing region were clarified. The results indicate that the main sources of nitrogen in the Lower Cambrian shale gas at the Southeast Chongqing region is the thermal evolution of organic matter and atmosphere. Nitrogen in the atmosphere is filled into the shale reservoir through migration channels formed by detachment layers at the bottom of the Lower Cambrian, shale stratification planes, and widespread thrust faults. Nitrogen was also produced during the thermal evolution of organic matter. Both are responsible for the low content of hydrocarbon and high content of nitrogen of shale gas in the Southeast Chongqing region. Further, the main sources of nitrogen in the Lower Cambrian shale gas at the Xiuwu Basin is the upper mantle, superdeep crust, and atmosphere. Nitrogen in the atmosphere is also filled into the shale reservoir through migration channels formed by detachment layers at the bottom of the Lower Cambrian, shale stratification planes, and widespread thrust faults. Nitrogen was also produced by volcanism during the Jurassic. Both are the causes of the low content of hydrocarbon and high content of nitrogen in shale gas in the Xiuwu Basin. Finally, destruction models for shale gas reservoirs with complex tectonic backgrounds were summarized. This research aimed to provide a theoretical guidance for shale gas exploration and development in areas with complex tectonic backgrounds.

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Provenance and tectonic setting of the Lower Cambrian Niutitang formation shales in the Yangtze platform, South China: Implications for depositional setting of shales

Geochemistry ◽

10.1016/j.chemer.2019.05.001 ◽

2019 ◽

Vol 79 (2) ◽

pp. 384-398 ◽

Cited By ~ 1

Author(s):

Lei Zhou ◽

Zongxiu Wang ◽

Wanli Gao ◽

Kaixun Zhang ◽

Huijun Li ◽

...

Keyword(s):

South China ◽

Lower Cambrian ◽

Tectonic Setting ◽

Yangtze Platform ◽

Niutitang Formation ◽

Depositional Setting

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Factors controlling organic matter enrichment in the Lower Cambrian Niutitang Formation Shale on the eastern shelf margin of the Yangtze Block, China

Interpretation ◽

10.1190/int-2017-0008.1 ◽

2017 ◽

Vol 5 (3) ◽

pp. T399-T410 ◽

Cited By ~ 3

Author(s):

Xianglu Tang ◽

Zhenxue Jiang ◽

Zhuo Li ◽

Lijun Cheng ◽

Ye Zhang ◽

...

Keyword(s):

Organic Matter ◽

Lower Cambrian ◽

Vertical Section ◽

Hydrothermal Activity ◽

Yangtze Block ◽

Anoxic Conditions ◽

Eastern Shelf ◽

Niutitang Formation ◽

Shelf Margin ◽

Water Contents

The degree of organic matter (OM) enrichment in shale determines its oil and gas potential. To understand the factors controlling this OM enrichment, we have used petrological and geochemical analyses to study the Lower Cambrian Niutitang Formation Shale in the eastern shelf margin of the Yangtze Block. Our results reveal that the total organic carbon (TOC) content of the Niutitang Formation Shale varies significantly throughout the vertical section. The lower part of the Niutitang Formation has a high TOC content, likely due to its formation in a dysoxic/anoxic environment with intense upwelling that favored OM enrichment. The middle part of the Niutitang Formation has the highest TOC content, which can be attributed to its formation in an environment with more hydrothermal activity, moderately upwelling, high paleosalinity, dysoxic/anoxic conditions, and moderately restricted water contents. Finally, the upper part of the Niutitang Formation records the lowest TOC contents because it likely formed in an oxic to dysoxic environment with weakly restricted hydrographic conditions that did not favor the preservation of OM. Therefore, these data demonstrate that the factors controlling OM enrichment in the Niutitang Formation Shale on the shelf margin include intense upwelling, greater amounts of hydrothermal activity, high paleosalinity, dysoxic/anoxic conditions, and moderately restricted water contents.

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Fractal characterization of pores in shales using NMR: A case study from the Lower Cambrian Niutitang Formation in the Middle Yangtze Platform, Southwest China

Journal of Natural Gas Science and Engineering ◽

10.1016/j.jngse.2016.09.030 ◽

2016 ◽

Vol 35 ◽

pp. 860-872 ◽

Cited By ~ 61

Author(s):

Lei Zhou ◽

Zhihong Kang

Keyword(s):

Lower Cambrian ◽

Southwest China ◽

Yangtze Platform ◽

Niutitang Formation

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Controls of Distinct Mineral Compositions on Pore Structure in Over-Mature Shales: A Case Study of Lower Cambrian Niutitang Shales in South China

Minerals ◽

10.3390/min11010051 ◽

2021 ◽

Vol 11 (1) ◽

pp. 51

Author(s):

Xing Niu ◽

Detian Yan ◽

Mingyi Hu ◽

Zixuan Liu ◽

Xiaosong Wei ◽

...

Keyword(s):

Organic Matter ◽

Pore Structure ◽

Clay Minerals ◽

Mineral Composition ◽

South China ◽

Lower Cambrian ◽

Great Influence ◽

Rock Composition ◽

Niutitang Formation ◽

Siliceous Shale

Investigating the impacts of rock composition on pore structure is of great significance to understand shale gas occurrence and gas accumulation mechanism. Shale samples from over-mature Niutitang formation of Lower Cambrian in south China were measured by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), low pressure N2 and CO2 adsorption to elucidate the controls of distinct mineral composition on pore development. Two distinct lithofacies, namely siliceous shale and argillaceous shale, were ascertained based on their mineral composition. Due to the variability of mineral composition in different lithofacies, pore structure characteristics are not uniform. Pores in siliceous shales are dominated by interparticle pores and organic matter (OM) pores, among which the interparticle pores are mainly developed between authigenic quartz. Furthermore, most of these interparticle pores and cleavage-sheet intraparticle pores within clay minerals are usually filled by amorphous organic matter that is host to OM pores. Due to the lack of rigid minerals, argillaceous shale was cemented densely, resulting in few interparticle pores, while cleavage-sheet intraparticle pores within clay minerals are common. Comparing siliceous shales with argillaceous shales, specific surface areas and pore volumes are higher on the former than on the latter. The content of total organic carbon (TOC) and authigenic quartz have a great influence on micropore structures, but less on mesopore structure for siliceous shales. The rigid framework structure formed by authigenic quartz is believed to be able to prevent primary interparticle pores from mechanical compaction and facilitate the formation of organic matter-associated pores. In terms of argillaceous shales, due to the lack of authigenic quartz, interparticle pores were rarely developed and its pore structure is mainly controlled by illite content.

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