Sedimentary environments and mechanism of organic matter enrichment of dark shales with low TOC in the Mesoproterozoic Cuizhuang Formation of the Ordos Basin: Evidence from petrology, organic geochemistry, and major and trace elements

Pan, Xing; Wang, Zhenliang; Li, Qiongyao; Gao, Jia; Zhu, Liwen; Liu, Wenhui

doi:10.1016/j.marpetgeo.2020.104695

Cited by 31 publications

(14 citation statements)

References 48 publications

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“…Sichuan Basin is currently a primary target area for shale gas exploration in China, with the lower Paleozoic Silurian Longmaxi Formation marine shale as the principal target strata. − The Longmaxi Formation in southeastern Sichuan Basin, China, possesses such natural advantages for shale gas development as wide distribution area, great effective thickness, and moderate burial depth. , Unlike conventional gas reservoirs, shale gas has the characteristics of “in situ accumulation”. Typically, shale gas is distributed in nanoscale pores and adsorbed on the surfaces of organic matter and mineral particles using “free state”, “adsorbed state”, and “dissolved state”. − Among them, contents of free gas and adsorbed gas are dominant, which are major types of shale gas exploitation at this stage. , Regardless of the form of shale gas, organic matter and inorganic minerals are hosting carriers of gas, which directly controls the development of reservoir spaces and the gas content of shale. , The mineral composition of shale is complicated, typically composed of quartz, clay minerals, feldspar, and calcite with a certain amount of pyrite. Nevertheless, marked differences can be found in pore types developed by various minerals and their contributions to porosity.…”

Section: Introductionmentioning

confidence: 99%

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Qin

et al. 2021

Energy Fuels

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Influences of the characteristics of organic matters and mineral compositions on the development of shale microscopic pores were discussed through performing low-temperature nitrogen adsorption, whole-rock "X" diffraction, and field emission scanning electron microscope on black organic-rich shale samples of Longmaxi Formation in the Dingshan area, southeastern Sichuan Basin, in combination with the characteristics of shale organic matters. The shale in the Dingshan area has complex mineral composition, which is mainly quartz and clay minerals. Both contents range from 23% to 72% and 36% to 70%, respectively. The vertical variation is obvious, and there are few feldspar and carbonate rocks; the pyrite content is more than 2%. The bottom shale has high brittleness and gradually decreases in the vertical direction. The brittleness index is between 0.481 and 0.627 and is concentrated above 0.5. It shows strong compressibility and is easy to form a complex network system in hydraulic fracturing. Quartz and feldspar mainly provide secondary dissolved pores, intercrystalline mineral pores, and nanoedge gaps in contact with organic matter. They have no obvious correlation with the specific surface area of shale but have a weak correlation with pore volume. They mainly control the development of macropores. Organic matter develops many hydrocarbon-generating pores, which strongly correlate with the specific surface area and a weak correlation with pore volume. It mainly controls the development of micromesopores. Clay minerals mainly provide a large number of interlaminar pores and interlayer fractures in the clay. The intergranular pores of clay and clay have a weak correlation with pore volume and specific surfaces. They contribute to the development of shale micropores, mesopores, and macropores. Pyrite mainly provides intercrystalline pores and mold pores. By restricting the interaction with organic matter, the development of shale pores is promoted within a certain content range. When the content exceeds this range, the development of micropores is inhibited. The conversion threshold in the Dingshan area is 5.0%.

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Section: Introductionmentioning

confidence: 99%

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Qin

et al. 2021

Energy Fuels

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“…Even in an oxic environment, sufficiently rich organic matter can form high TOC marine sediments, and the rich organic matter can consume oxygen as it decomposes. , Meanwhile, the organic matter input from terrestrial sources during the deposition of the Dawuba Formation compensated for the unfavorable conditions in the oxidation environment during the sedimentation period. It enhanced the organic matter content in the mudstone and shales of the Dawuba Formation.…”

Section: Discussionmentioning

confidence: 99%

Sedimentation Models and Development Mechanisms of Organic-Rich Shales of the Lower Carboniferous Dawuba Formation: A Case Study in the Yaziluo Rift Trough, South of Guizhou Province, Southern China

et al. 2022

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China has made a breakthrough in shale gas production in the deepwater shelf shales of the Lower Cambrian Qiongzhusi Formation and the Upper Ordovician–Early Silurian Wufeng–Longmaxi Formation. In recent years, active shale oil and gas shows have also been found in the shale system of the Lower Carboniferous Dawuba Formation in the Yaziluo rift trough, south of Guizhou province in Southern China, which was formed in the tensional geotectonic setting of the Palaeo-Tethys Ocean from the Devonian through the Carboniferous to the Permian. This tectonic background makes the sedimentary environments and organic matter accumulation mechanisms of Dawuba shales vastly different from deepwater shales. To better understand the deposition and organic matter accumulation mechanisms of marine shale developed in the rift trough, we carried out detailed field surveys and drilling data interpretation to study the lithological assemblage, organic matter, and elemental geochemical characteristics of Dawuba shales. The results show the following: (1) The study area is located in a platform–slope–basin depositional model like the Florida–Bahama platform–trough system of the west Atlantic margin, with a rapidly geomorphologic variation from basin to bank, dominated by a coastal sandstone and mudstone system in the northwest, a marlite and mudstone slope system around the rift trench (Liupanshui county), and a deep water fine-grained-turbidite system in the southeast (Ziyun county). (2) Major element (ME), trace element (TE), and rare earth element (REE) data indicate significant terrestrial source material input [total organic carbon (TOC) correlates well with Ti/Al], high deposition rates [mean (La/Yb) N of 1.41], and complex oxic-dysoxic conditions (U/Th mainly between 0 and 0.5), which illustrate substantial terrigenous sedimentary input and changes in redox conditions in deep water. (3) The input of organic matter from terrestrial sources in the study area is predominant compared with internal basin-originated organic matter, and the organic matter type is mainly Type II 2 or Type III. Stable carbon isotope (δ 13 C carb ) data of carbonate rocks also indicates that the widely developed upwelling in this region brings abundant nutrients, which also contributes to organic matter enrichment. Organic-rich shales exist in the Yaziluo rift trough under the influence of strong tensile action. The results of the study are essential for understanding the sedimentology and hydrocarbon exploration in similar rift trough areas within the Paleo-Tethys Ocean.

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“…Paleoproductivity refers to the total amount of organic matter fixed per unit area per unit time (Algeo et al, 2011;Pan et al, 2020). Generally speaking, high organic productivity is one of the key factors for the formation of hydrocarbon source rocks (Talbot, 1988;Nelson et al, 1995;Mansour et al, 2020a;Mansour et al, 2020b;Yang et al, 2016;Zhao et al, 2021), and a large number of studies have shown that siliceous plankton in marine source rocks is the main provider of marine primary productivity (De Wever and Baudin, 1996;Chou et al, 2012;Xiang et al, 2013;Shaldybin et al, 2017;Jiang et al, 2019;Zhang et al, 2019), whose content is closely related to the biological reproduction in surface water, and its temporal and spatial distribution can be used to reflect the changing process of paleoproductivity.…”

Section: Relationship Between Biogenic Silica and Organic Mattermentioning

confidence: 99%

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

Zhang

Huang

et al. 2021

Front. Earth Sci.

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The shale of the Wulalike Formation developed in the northwestern Ordos Basin is considered to be an effective marine hydrocarbon source rock. One of the key factors for successful shale gas exploration in the Wufeng–Longmaxi Formation in the Sichuan Basin is the high content of biogenic silica. However, few people have studied the siliceous origin of the Wulalike shale. In this study, we used petrographic observation and element geochemistry to analyze the origin of silica in the Wulalike shale. The results show that the siliceous minerals are not affected by hydrothermal silica and mainly consist of biogenic and detrital silica. A large number of siliceous organisms, such as sponge spicules, radiolarians, and algae, are found under the microscope. It has been demonstrated that total organic carbon has a positive correlation with biogenic silica and a negative correlation with detrital silica, and biogenic silica is one of the effective indicators of paleoproductivity. Therefore, the enrichment of organic matter may be related to paleoproductivity. Through the calculation of element logging data in well A, it is found that biogenic silica is mainly distributed in the bottom of the Wulalike Formation, and the content of biogenic silica decreases, while the content of detrital silica increases upward of the Wulalike Formation. Biogenic silica mainly exists in the form of microcrystalline quartz, which can form an interconnected rigid framework to improve the hardness and brittleness of shale. Meanwhile, biogenic microcrystalline quartz can protect organic pores from mechanical compaction. Therefore, it may be easier to fracture the shale gas at the bottom of the Wulalike Formation in well A.

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Sedimentary environments and mechanism of organic matter enrichment of dark shales with low TOC in the Mesoproterozoic Cuizhuang Formation of the Ordos Basin: Evidence from petrology, organic geochemistry, and major and trace elements

Cited by 31 publications

References 48 publications

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Sedimentation Models and Development Mechanisms of Organic-Rich Shales of the Lower Carboniferous Dawuba Formation: A Case Study in the Yaziluo Rift Trough, South of Guizhou Province, Southern China

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

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