Preservation of organic carbon in the Cretaceous Hue Shale on the North Slope of Alaska: Insights from pyrite morphology

Song, Liaosha; Bhattacharya, Shuvajit; Webb, Zachary; Fowler, Austin G.; Lee, Victoria

doi:10.1016/j.coal.2021.103678

Cited by 11 publications

(3 citation statements)

References 37 publications

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“…Pyrite, a crucial redox-sensitive mineral in the marine organic-rich shale, is usually developed associated with the organic matter of shale. And its development morphology and content can affect the organic matter pyrolysis and hydrocarbon generating process and provide a certain amount of reservoir spaces by indicating shale sedimentation and diagenetic environment . In general, pyrites in the organic-rich shale are developed in clusters, forming strawberry-like pyrite crystals.…”

Section: Discussionmentioning

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: Discussionmentioning

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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“…Framboidal pyrite is generally considered to have formed during syn-sedimentary and early diagenetic stages, with a small grain size and negative sulfur isotopes. In contrast, spherulitic, euhedral, and anhedral pyrites may have formed during diagenesis when framboidal pyrite microcrystals increase in size or directly crystallize in sulfur-bearing waters when the concentration of reactive iron is low, with a large grain size and negative sulfur isotopes. ,− In addition, Taotao et al (2018) used scanning electron microscopy (SEM) to determine that type I and type II organic matter constituted an organic/pyrite complex with framboidal pyrite, forming a group around pyrite in the core as a whole, which was conducive to liquid hydrocarbon enrichment. In contrast, type III organic matter mostly appeared as contours and framboidal pyrite was rare .…”

Section: Introductionmentioning

confidence: 99%

Pyrite Characteristics in Lacustrine Shale and Implications for Organic Matter Enrichment and Shale Oil: A Case Study from the Triassic Yanchang Formation in the Ordos Basin, NW China

Zhou,

Liu,

et al. 2024

ACS Omega

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Pyrite is widely distributed in lacustrine shales and has become a research focus in unconventional oil and gas exploration. Pyrite morphology is useful for identifying different types of organic matter and assessing shale oil enrichment in organic-rich shale. Abundant pyrite is developed in the source rocks from the Chang 7 Member of the Yanchang Formation in the Ordos Basin, NW China. However, the relationship between different pyrite types and the differential enrichment of shale oil still needs to be clarified. The organic geochemistry, petrology, and isotopic composition of the Chang 7 Member samples were analyzed. The significance of pyrite types and sulfur isotopic compositions as indicators of depositional environments and shale oil enrichment was emphasized. The Chang 7 shales contain three pyrite morphologies, framboidal pyrite (type A), spherulitic pyrite (type B), and euhedral and anhedral pyrite (type C), and their aggregates. The sulfur isotopic compositions of pyrite (δ 34 S py ) in Chang 7 shales with different pyrite types exhibited regular patterns. The δ 34 S values of types A, B, and C pyrites were sequentially positive overall (average values are −2.739, 2.201, and 7.487‰ in sequence), indicating that type A pyrite was formed during the syn-sedimentary to early diagenetic stage and types B and C pyrites were formed during the early to middle diagenetic stage. Types A, B, and C pyrites showed sequentially increasing kerogen type index values and kerogen carbon isotope values (mean values of −31.59, −28.70, and −26.45‰, successively), indicating that the horizons where types A, B, and C pyrites developed correspond to types I, II, and III organic matter, respectively. Strong correlations between the pyrite content and oil components reveal that pyrite indicates shale oil enrichment. Moreover, variations in pyrite type significantly influenced the enrichment behavior of shale oil. Types A and B pyrites contributing to reservoir space showed shale oil enrichment. They promoted saturated hydrocarbon enrichment at >15% pyrite content, whereas type C pyrite did not indicate shale oil enrichment. These findings provide new insights into the differential enrichment of organic matter and shale oil and valuable guidance for the large-scale exploration and development of shale oil resources.

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“…Previous studies have made great progress in understanding the geological characteristics of shale reservoirs; defined the geochemical characteristics, mineralogical characteristics, and reservoir space characteristics of the reservoirs; found that the sedimentary environment, organic matter (OM), clay minerals, brittle minerals, and fractures are the main controlling factors of shale reservoir yields; and formed a comprehensive research system for shale reservoirs (Chen et al, 2016;Li et al, 2019c;Chen S. L. et al, 2020;Li et al, 2020;Liu et al, 2020;Chen et al, 2021a;Chen et al, 2021b;Liu J. et al, 2021;Sun, 2021). However, these research results and conclusions apply mainly to shallow shale gas with a burial depth of less than 3,500 m. Due to the influence of sedimentation, diagenesis, and tectonism, deep shale gas reservoirs have higher contents of brittle minerals, more developed natural fractures, and more complex pore evolution, resulting in different shale geological characteristics and controlling factors for shale gas enrichment and yield (Yin et al, 2019;Chen F. et al, 2020;Chai et al, 2020;Xu and Gao, 2020;Yin and Wu, 2020;Zhou et al, 2020;Song et al, 2021;Tabatabaei 2021). Therefore, clarifying the geological characteristics of deep shale is needed to explore and extract deep shale gas.…”

Section: Introductionmentioning

confidence: 99%

Geological Characteristics and Controlling Factors of Enrichment of Deep Shale Gas in the East Weiyuan–North Rongchang Area, Sichuan Basin, China

Tang

Li³

et al. 2022

Front. Earth Sci.

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The southern Sichuan Basin is the core area of China’s efficient development of deep shale gas (burial depth greater than 3,500 m). Reservoir geological characteristics determine whether shale gas can be preserved, enriched, and produced. Taking the Long 11 sub-member of the Wufeng Formation of the Upper Ordovician and the Longmaxi Formation of the Lower Silurian in the East Weiyuan–North Rongchang area as an example, we used the core, logging, production test, and other data, combining X-ray diffraction analysis, LECO Total Organic Carbon (TOC)-S analysis, optical microscopy, and argon ion polishing field-emission scanning electron microscopy, to study the shale mineral composition, geochemistry, reservoir space, pore structure characteristics, and reservoir physical properties. The following results were obtained: 1) The brittle mineral content, organic matter maturity, and TOC content are high, gradually increase from top to bottom, and reach their maxima at small layer 1 of Long 11. 2) Organic pores, inorganic pores, and fractures are important reservoir spaces, among which organic pores and fractures are important seepage channels for shale gas. 3) The shale pore structure revealed by electron microscopy shows that the pore structure in target layers can be divided into four types: unimodal type (mainly organic pores), bimodal type (both organic and inorganic pores), monoclinic type I (mainly organic pores), and monoclinic type II (mainly inorganic pores). The pore morphology is complex, and circular and oval shapes predominate. 4) Sedimentary facies are the main factor controlling the enrichment of shale gas, and the development of fractures is the key to obtaining high yields of shale gas. 5) The class I favorable target area is mainly distributed in wells W206, W206H1, R234H, and R233H and areas to its south, and some areas in the east of the study area.

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Preservation of organic carbon in the Cretaceous Hue Shale on the North Slope of Alaska: Insights from pyrite morphology

Cited by 11 publications

References 37 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

Pyrite Characteristics in Lacustrine Shale and Implications for Organic Matter Enrichment and Shale Oil: A Case Study from the Triassic Yanchang Formation in the Ordos Basin, NW China

Geological Characteristics and Controlling Factors of Enrichment of Deep Shale Gas in the East Weiyuan–North Rongchang Area, Sichuan Basin, China

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