Article pubs.acs.org/EF
Cite This: Energy Fuels XXXX, XXX, XXX−XXX
Comprehensive Understanding of OM-Hosted Pores in Transitional Shale: A Case Study of Permian Longtan Shale in South China Based on Organic Petrographic Analysis, Gas Adsorption, and X‑ray Diffraction Measurements Chao Yang,† Yongqiang Xiong,*,† Jinchuan Zhang,‡ Yuke Liu,† and Cong Chen§
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State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People’s Republic of China ‡ School of Energy Resources, China University of Geosciences, Beijing 100083, People’s Republic of China § Shenzhen Branch of China National Offshore Oil Corporation Ltd., Shenzhen 518000, People’s Republic of China ABSTRACT: Marine-continental transitional (hereinafter referred to as transitional) Permian shales are the important targets for shale gas in China. However, the nature and formation of organic matter (OM)-hosted pores in this shale facies have not yet been studied in detail from the perspectives of organic petrology and geochemistry. In this paper, we selected typical transitional shale samples from the Permian Longtan Formation in the northwestern Guizhou province to investigate the development of OM-hosted pores mainly through organic petrographic analysis, gas adsorption, and X-ray diffraction (XRD) measurements. Petrographic observations under an optical microscope and a scanning electron microscope (SEM) reveal that the OM in the Longtan shale is composed predominantly of type III kerogens (vitrinite and inertinite), with minor amounts of amorphous solid bitumen. SEM imaging reveals that secondary OM pores (as a result of devolatilization of gaseous hydrocarbons) were very rare in Longtan shale, being only occasionally observed in individual type III kerogens with a bubble-like morphology. This phenomenon is most likely attributed to the chemical-inert body of type III kerogens that cannot depolymerize during thermal degradation. On the other hand, the high methane adsorption values and their strong linear correlation with total organic carbon contents in the Longtan shale indicate that the type III kerogens contain numerous SEM-invisible micropores (
