Organic Matter Pores Developments of Lower Silurian Longmaxi Shale in Southeast Chongqing: Based on Focused Ion Beam Helium Ion Microscopy (FIB-HIM)

doi:10.19657/j.geoscience.1000-8527.2019.04.21

Abstract

Abstract:

Organic matter pores in shale are critical to the occurrence of hydrocarbon gases. The focused ion beam helium ion microscope (FIB-HIM) technique was used to determine the organic matter pore development features of the Lower Silurian Longmaxi Formation (Fm.) shale in southeastern Chongqing. The sub-nanometer resolution of FIB-HIM can effectively identify pores with 0-20 nm diameter. The results show a large amount of organic matter pores inside the pyrobitumen of the Longmaxi Fm. shale. The organic matter pore diameter is large with good connectivity. A large number of smaller pores are nested in the larger pores, which increases the connectivity of the pore system. The specific surface area and pore connectivity are beneficial to the occurrence and effective seepage of hydrocarbon gases in the pores. Development characteristics of the organic matter pores in solid kerogen of the Longmaxi Fm. shale are considerably different from those of the pyrobitumen. The organic matter pores developed in the solid kerogen are small in both size and number, and with poor connectivity that the pores are mostly isolated inside the solid kerogen.

Key words: southeastern Chongqing, Longmaxi Fm. shale, solid kerogen, pyrobitumen, organic matter pore, FIB-HIM

CLC Number:

TE121.2

WANG Pengfei, JIANG Zhenxue, JIN Can, LÜ Peng, LI Xin, ZHANG Kun, WANG Kai, HUANG Pu. Organic Matter Pores Developments of Lower Silurian Longmaxi Shale in Southeast Chongqing: Based on Focused Ion Beam Helium Ion Microscopy (FIB-HIM)[J]. Geoscience, 2019, 33(04): 902-910.

Figures/Tables 9

Fig.1 Geological map of the study area in southeastern Chongqing and the well distribution in the Longmaxi Fm. shale

Fig.2 Frequency distribution of the TOC content in the Longmaxi Fm. shale samples

Fig.3 Bulk-rock mineral composition of the Longmaxi Fm. shale samples

Fig.4 Frequency distribution of thermal maturities(Equa-Ro) of the Longmaxi Fm. shale samples

Fig.5 Focused ion beam helium ion microscopy (FIB-HIM)

Fig. 6 Development features of solid kerogen and its organic matter pores in the Longmaxi Fm. shale samples

Fig.7 Pyrobitumen and organic matter pore development characteristics of the Longmaxi Fm. shale samples based on FIB-HIM

Fig.8 Organic matter pore development characteristics of pyrobitumen in the Longmaxi Fm. shale samples based on high resolution FIB-HIM

Fig.9 Pyrobitumen and organic matter pore development characteristics of the Longmaxi Fm. shale samples based on FIB-SEM

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