Origin of organic matter and organic pores in the overmature Ordovician-Silurian Wufeng-Longmaxi Shale of the Sichuan Basin, China

Teng, Juan; Liu, Bei; Mastalerz, Maria; Schieber, Juergen

doi:10.1016/j.coal.2022.103970

Origin of organic matter and organic pores in the overmature Ordovician-Silurian Wufeng-Longmaxi Shale of the Sichuan Basin, China

Journal Article · Fri Mar 11 00:00:00 EST 2022 · International Journal of Coal Geology

DOI:https://doi.org/10.1016/j.coal.2022.103970· OSTI ID:1861305

Teng, Juan ^[1]; Liu, Bei ^[2]; Mastalerz, Maria ^[3]; Schieber, Juergen ^[3]

Yangtze Univ., Hubei (China); Indiana Geological and Water Survey, Indiana University
China Univ. of Geosciences, Hubei (China); Indiana Univ., Bloomington, IN (United States)
Indiana Univ., Bloomington, IN (United States)

Organic matter (OM)-hosted pores play important roles in controlling the porosity and gas content of gas shales. However, the control of organic pore development and preservation remains poorly understood, partly because of the inability to distinguish OM types under the scanning electron microscope (SEM). In this study, seven over-mature Wufeng-Longmaxi Shale samples (equivalent vitrinite reflectance 1.93%–3.07%) were investigated with organic petrography and scanning electron microscope to study the origin of OM and development of organic pores in this black shale succession. Correlative light and electron microscopy was employed to examine pore development in individual macerals. Organic petrographic observations show that OM in these over-mature black shales is dominated by pyrobitumen and graptolites (> 90 vol.% of total OM based on point counting). Pyrobitumen mainly occurs as matrix bitumen in the fine-grained matrix, and also as a mixture with clay minerals and fossil cavity infillings. Vitrinite-like particles are minor constituents of OM in the Wufeng-Longmaxi Shale, and their average reflectance, reflectance distribution, and morphology suggest that they may be derived from graptolite fragments lacking diagnostic features and acritarchs. OM type critically controls the development of organic pores. Here, organic pores primarily occur in pyrobitumen, whereas other macerals are mostly non-porous when examined under the SEM. Results of this study provided important insights into OM thermal evolution and organic pore development in source-rock reservoirs, calling for a critical appraisal of OM in black shales with organic petrography in addition to SEM.

View Accepted Manuscript (DOE)

Research Organization:: Indiana Univ., Bloomington, IN (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: SC0006978

OSTI ID:: 1861305

Journal Information:: International Journal of Coal Geology, Journal Name: International Journal of Coal Geology Vol. 253; ISSN 0166-5162

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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Wufeng-Longmaxi Shale

Origin of organic matter and organic pores in the overmature Ordovician-Silurian Wufeng-Longmaxi Shale of the Sichuan Basin, China

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