Mineralogical and petrographic characteristics of the Ordovician-Silurian Wufeng-Longmaxi Shale in the Sichuan Basin and implications for depositional conditions and diagenesis of black shales

Qiu, Zhen; Liu, Bei; Lü, Bin; Shi, Zhensheng; Li, Zhiyang

doi:10.1016/j.marpetgeo.2021.105428

Cited by 27 publications

(12 citation statements)

References 60 publications

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“…Specifically, Figure 4 exhibits a large amount of gray‐black OM irregularly distributed in the minerals and well‐developed pores of different diameters in the OM. Generally, the oil‐prone OM transforms into hydrocarbons and pyrobitumen after the peak oil windows, while gas‐prone OM and inert macerals exhibit no significant changes in morphology owing to their low hydrocarbon generation potential 29 . These OM‐hosted pores are formed during thermal maturation because of gas generation and expulsion.…”

Section: Resultsmentioning

confidence: 99%

“…Currently, the Lower Silurian Longmaxi Formation is the main producing layer of the Weiyuan‐Changning, Fuling, and other shale gas fields and can be regarded as the most potential target region for shale gas exploration and development. The Longmaxi Formation shale was formed in an anoxic, low‐energy shallow‐water‐deep‐water continental shelf facies sedimentary environment and was controlled by depositional and diagenetic processes 29 …”

Section: Geological Settingmentioning

confidence: 99%

“…Currently, the Upper Ordovician Longmaxi Formation in the Sichuan Basin of China is considered to exhibit the most favorable conditions for shale gas enrichment and production. Several researchers have explored the pore structure characteristics of Longmaxi shale to develop precise development strategies for shale gas reservoirs 12,27–29 . Different shale lithofacies generally display distinct pore structure features, and the development of OM pores is closely related to thermal maturity and OM types 27,30 .…”

Section: Introductionmentioning

confidence: 99%

“…Several researchers have explored the pore structure characteristics of Longmaxi shale to develop precise development strategies for shale gas reservoirs. 12,[27][28][29] Different shale lithofacies generally display distinct pore structure features, and the development of OM pores is closely related to thermal maturity and OM types. 27,30 Furthermore, several studies have reported that mineral pores in the shale matrix cannot provide efficient seepage channels for gas production, whereas OM pores determine the connectivity in shale.…”

Section: Introductionmentioning

confidence: 99%

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Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

Hui

Zhang²,

Hu³

et al. 2022

Energy Science & Engineering

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Knowledge of shale pore structure characteristics is crucial to understand gas storage and seepage mechanisms. Organic matter (OM) pores are considered the most important pore type in shale, and one of the currently significant research questions focuses on the spatial distribution and connectivity of OM pores. To answer this question, typical OM‐rich siliceous shale samples from the Lower Silurian Longmaxi Formation were comprehensively investigated using focused ion beam scanning electron microscopy. A three‐dimensional model of the OM‐rich region of interest was segmented and reconstructed based on numerous two‐dimensional slices. The types of OM were found to control the development of organic pores, and OM pores including honeycomb‐shaped pores, spongy‐shaped pores, and slit‐like irregular pores are mainly formed in the pyrobitumen. The pore structure parameters of the OM‐rich ROI revealed that the pore size distribution of honeycomb‐shaped OM pores formed in the pyrobitumen was mainly distributed in the range of 10–50 and 80–100 nm, while the throat equivalent diameter distribution demonstrated a unimodal curve with the main peak located at approximately 30 nm. Pore connectivity analysis further indicated that pyrobitumen also contained several isolated nano‐pores, and pores with diameters smaller than 40 nm were poorly connected. Furthermore, permeability simulation revealed clear discrepancies in different directions owing to the heterogeneity of the OM pores. These findings provide experimental evidence for the assessment of shale gas resources and their development potential.

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Section: Resultsmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

Hui

Zhang²,

Hu³

et al. 2022

Energy Science & Engineering

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“…The Wufeng–Longmaxi shale experienced mechanical compaction, pyrite cementation, and biologic opal recrystallization during early diagenesis, montmorillonite illitization, quartz overgrowth, and hydrocarbon generation during middle digenesis, and ankerite replacement and liquid hydrocarbon thermal cracking during late diagenesis. , An R o value higher than 2.0% and illite crystallinity ranging from 0.27 to 0.37 indicates that the Wufeng–Longmaxi shale is in late diagenesis. , The diagenesis and changes in mineral composition induced by diagenesis will have an obvious impact on OM pore development.…”

Section: Discussionmentioning

confidence: 99%

Identifying Organic Matter (OM) Types and Characterizing OM Pores in the Wufeng–Longmaxi Shales

Guoliang

Hao

2022

ACS Omega

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Organic matter (OM) pores are considered to be an important pore type in the Ordovician Wufeng–Silurian Longmaxi Formation shales in the Sichuan Basin, China, because they have a high capacity to store natural gas. However, to the best of our knowledge, research on the characterization and quantitation of different OM pore characteristics is insufficient. In this study, detailed optical microscope and scanning electron microscope (SEM) observations and the pores/particles and cracks analysis system (PCAS) were applied to identify the OM pores and obtain quantitative information on pores such as pore size, surface porosity, form factor, and probability entropy. Moreover, CO2 and N2 adsorption experiments were performed to study the properties of pores for samples with different TOC and mineral compositions. The results show the following. (1) Pyrobitumen and kerogen can be distinguished under an optical microscope and SEM; the former can be further divided into pyrobitumen without a fixed shape and pyrobitumen with a certain shape, and the latter contains algal fragments, bacteria-like aggregates, graptolite, and micrinite. The overwhelming number of SEM-visible OM pores are mainly observed in pyrobitumen without a fixed shape, whereas pores in other OM types are complex. A PCAS analysis showed that meso-macropores are developed in pyrobitumen without a fixed shape, whereas pores in algal fragments and bacterial-like aggregates are mainly mesopores. (2) Quartz-rich brittle shale will provide more visible SEM pores compared to clay-rich ductile shale, and carbonates are unfavorable for pore development because they can block the pore as cements. Moreover, the rigid mineral framework, including that constructed by quartz recrystallization and pyrite cementation, and the pore-fluid pressure are favorable for the development of OM pores. (3) Adsorption experiments showed that pyrobitumen makes a great contribution to pore development, including micropores and meso-/macropores. Finally, we propose that the pore parameters (e.g., pore diameter, pore form factor, and deformation) of pyrobitumen without a fixed shape may characterize the enrichment condition of shale gas.

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Shale mineral particles directional arrangement and its effect on the mesoscopic failure mechanism

Li,

Wang,

Xue

et al. 2024

Bull Eng Geol Environ

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Mineralogical and petrographic characteristics of the Ordovician-Silurian Wufeng-Longmaxi Shale in the Sichuan Basin and implications for depositional conditions and diagenesis of black shales

Cited by 27 publications

References 60 publications

Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

Identifying Organic Matter (OM) Types and Characterizing OM Pores in the Wufeng–Longmaxi Shales

Shale mineral particles directional arrangement and its effect on the mesoscopic failure mechanism

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