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The architecture of organic matter and its pores in highly mature gas shales of the Lower Silurian Longmaxi Formation in the upper Yangtze Platform, south China

Ji Wenming, Hao Fang, Hans-Martin Schulz, Song Yan and Tian Jinqiang
The architecture of organic matter and its pores in highly mature gas shales of the Lower Silurian Longmaxi Formation in the upper Yangtze Platform, south China
AAPG Bulletin (December 2019) 103 (12): 2909-2942

Abstract

The nanometer-scale architecture of organic matter and associated pores in highly mature gas shales from the lower Silurian Longmaxi Formation in the upper Yangtze platform, south China were investigated using field emission scanning electron microscopy (FE-SEM), focused ion beam scanning electron microscopy (FIB-SEM) and low pressure gas (N (sub 2) and CO (sub 2) ) adsorption bulk pore characterization. The Longmaxi shale comprises fine-grained siliciclastic rocks deposited in a marine shelf environment, which was dominated by quartz and clay minerals. Four porous organic matter (OM) types were found in the Longmaxi shale on the basis of the chemical composition and spatial occurrence of organic matter, including (1) isolated original OM particles, (2) OM-clay mineral complexes, (3) OM-heavy mineral complexes and (4) secondary migrated bituminous OM. The pores in the particulate OM are not homogeneously distributed and the processes leading to different pores depend on the specific OM type. The nature of OM-hosted pores is result of several factors such as primary porous kerogen, mechanical compaction, organic-inorganic interactions, gaseous and liquid hydrocarbon generation, retention and expulsion. Pore volumes and specific surface areas of the Longmaxi shale derived from low pressure N (sub 2) and CO (sub 2) adsorption experiments reveal positive linear relationships with TOC contents, which indicates that the pore systems in the highly mature Longmaxi shale are dominated by OM-hosted pores. Additionally, the OM-hosted pores appear connected compared to pores in the mineral matrix. Therefore, the OM-hosted pore systems offer the preferential storage space and primary migration pathways for natural gas in the Longmaxi shale reservoir.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 103
Serial Issue: 12
Title: The architecture of organic matter and its pores in highly mature gas shales of the Lower Silurian Longmaxi Formation in the upper Yangtze Platform, south China
Affiliation: China University of Petroleum, School of Geosciences, Laboratory for Marine Mineral Resources, Shandong, China
Pages: 2909-2942
Published: 201912
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 104
Accession Number: 2019-089021
Categories: Economic geology, geology of energy sourcesSedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. chart, sect., 2 tables, sketch maps
N28°19'60" - N29°45'00", W107°15'00" - E109°45'00"
Secondary Affiliation: German Research Centre for Geosciences, DEU, GermanyPetroChina, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 2019
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