Controls on U enrichment in organic-rich shales from the Triassic Yanchang Formation, Ordos Basin, Northern China

Yuan, Wang; Liu, Guangdi; Bulseco, Ashley; Xu, Liming; Zhou, Xiaoxing

doi:10.1016/j.jseaes.2021.104735

Cited by 7 publications

(3 citation statements)

References 38 publications

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“…As a result, the contents of these elements in the sediments will be abnormally and radially distributed around the center of the hydrothermal fluid input channel. Thus, anomalous abundances of these elements are one of the most important geochemical characteristics of hydrothermal sediments and can be used to distinguish between hydrothermal sediments and normal sediments [26,[54][55][56]. In contrast to normal sediments, hydrothermal sediments are generally enriched in elements such as Si, Mn, P, Pb, Zn, Cu, Ba, Fe, Sr, and U, while they are depleted in elements such as Al, Ti, Mg, Cr, Th, Zr, and Rb.…”

Section: Hydrothermal Influencesmentioning

confidence: 99%

Depositional Environment and Organic Matter Enrichment of Early Cambrian Niutitang Black Shales in the Upper Yangtze Region, China

et al. 2022

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Natural gas generation is the result of organic matter degradation under the effects of biodegradation and thermal degradation. Early Cambrian black shales in the Upper Yangtze Region are rich in organic matter and have shown great shale gas potentiality in recent years. Nevertheless, the enrichment mechanism and distribution of organic matter in these black shales between different sedimentary settings, such as intra-platform basin, slope, and deep basin, are still poorly understood. In this paper, based mainly on elemental geochemistry, a comprehensive study of the marine redox conditions, primary productivity, sedimentation rate, terrigenous input, hydrothermal activity, and water mass restrictions was conducted on the Early Cambrian Niutitang black shale in the Upper Yangtze Region. Our data showed that an intra-platform basin received a higher terrigenous input and that it deposited under more restricted conditions than the slope and deep basin settings. The primary productivity in the slope and deep basin settings was higher than that in the intra-platform basin setting. In the intra-platform basin, the productivity increased from its inner part to its margin. For the slope and deep basin settings, the high paleoproductivity generated large amounts of organic matter and its preservation was synergistically affected by the redox conditions. In contrast to the slope and deep basin, the preservation of organic matter in the inner part of the intra-platform basin was mainly controlled by redox conditions because the paleoproductivity in it was much lower than in the slope and deep basin settings. The intra-platform basin margin was the most favorable area for accumulating organic matter.

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Section: Hydrothermal Influencesmentioning

confidence: 99%

Depositional Environment and Organic Matter Enrichment of Early Cambrian Niutitang Black Shales in the Upper Yangtze Region, China

et al. 2022

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“…Before heating, the mineral composition was mainly pyrite (39.0%), quartz (28.2%), and clay (21.1%), with small amounts of plagioclase, K-feldspar, ankerite, and siderite accounting for 11.6% in total (Figure 4). Previous studies have shown that the high pyrite content of the Chang 7 shale from the Ordos Basin has promoted the generation, discharge, and accumulation of the medium-high-maturity shale oil [43,44].…”

Section: Changes In Mineral Compositionmentioning

confidence: 99%

Heat-Induced Pore Structure Evolution in the Triassic Chang 7 Shale, Ordos Basin, China: Experimental Simulation of In Situ Conversion Process

Zhao

Hou

et al. 2023

JMSE

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The reservoir properties of low–medium-maturity shale undergo complex changes during the in situ conversion process (ICP). The experiments were performed at high temperature (up to 450 °C), high pressure (30 MPa), and a low heating rate (0.4 °C/h) on low–medium-maturity shale samples of the Chang 7 Member shale in the southern Ordos Basin. The changes in the shale composition, pore structure, and reservoir properties during the ICP were quantitatively characterized by X-ray diffraction (XRD), microscopic observation, vitrinite reflectance (Ro), scanning electron microscopy (SEM), and reservoir physical property measurements. The results showed that a sharp change occurred in mineral and maceral composition, pore structure, porosity, and permeability at a temperature threshold of 350 °C. In the case of a temperature > 350 °C, pyrite, K-feldspar, ankerite, and siderite were almost completely decomposed, and organic matter (OM) was cracked into large quantities of oil and gas. Furthermore, a three-scale millimeter–micrometer–nanometer pore–fracture network was formed along the shale bedding, between OM and mineral particles and within OM, respectively. During the ICP, porosity and permeability showed a substantial improvement, with porosity increasing by approximately 10-times and permeability by 2- to 4-orders of magnitude. Kerogen pyrolysis, clay–mineral transformation, unstable mineral dissolution, and thermal stress were the main mechanisms for the substantial improvement in the reservoir’s physical properties. This study is expected to provide a basis for formulating a heating procedure and constructing a numerical model of reservoir properties for the ICP field pilot in the Chang 7 shale of the Ordos Basin.

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“…Moreover, sandstones interbedded with shales may have a direct association with the environmental or climatic conditions. ,− Some research indicated that a humid climatic regime prevailed during the deposition of the Chang 7. , However, further sedimentological studies are still required to validate these findings. In general, paleoenvironment reconstructions in black shales using these rocks are based on inorganic geochemical techniques. − The redox conditions, water depth, detrital flux, and primary productivity during sediment deposition can all be determined by using this method. According to studies, the structure and composition of sandstones in black shales can be utilized to limit the sedimentary depositional environment. , Moreover, the mineralogy of the sediments reflects the terrestrial environment and climate .…”

Section: Introductionmentioning

confidence: 99%

The Lithofacies of Sandstones Interbedded with Shales: Implication for Organic Matter Accumulation of Triassic Deep Lacustrine Setting, Southern Ordos Basin

Pang,

Hu,

et al. 2024

ACS Omega

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The sandstones interbedded with shales in the lacustrine black shale have great potential to become important targets for oil and gas exploration, but there has been a lack of systematic research regarding their types and genesis. This study focused on the investigation of the Triassic Chang 7 3 member deep lacustrine sandstone. Eleven lithofacies are identified and classified into three different types of deposits: ash fall and intra-and extra-basinal turbidite deposits. Vitric tuff, pumice-bearing shale, and ash are the main ash fall lithofacies. The presence of reverse grading and a significant concentration of plant fragments/micas suggest extra-basinal turbidite deposits. However, the collapse of deltaic intrabasinal sediments has been well sorted and does not contain plant debris and low-density materials. These three different types of sediments combined with a humid climate are the main causes for the deposition of a large number of sandstone layers in the deep lacustrine environment. Furthermore, the abundant volcanic eruptions are associated with increased organic matter accumulation and promoted the bloom of algae. In addition, the generated oil in the black shales would then migrate and accumulate in the interbedded sandstones. This research provides geological evidence for the prospective prediction of lacustrine shale oil accumulations.

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Controls on U enrichment in organic-rich shales from the Triassic Yanchang Formation, Ordos Basin, Northern China

Cited by 7 publications

References 38 publications

Depositional Environment and Organic Matter Enrichment of Early Cambrian Niutitang Black Shales in the Upper Yangtze Region, China

Depositional Environment and Organic Matter Enrichment of Early Cambrian Niutitang Black Shales in the Upper Yangtze Region, China

Heat-Induced Pore Structure Evolution in the Triassic Chang 7 Shale, Ordos Basin, China: Experimental Simulation of In Situ Conversion Process

The Lithofacies of Sandstones Interbedded with Shales: Implication for Organic Matter Accumulation of Triassic Deep Lacustrine Setting, Southern Ordos Basin

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