Chemical compositions and distribution characteristics of cements in longmaxi formation shales, Southwest China

Zhou, Wenda, Xie, Shuyun, Bao, Zhengyu, Carranza, Emmanuel John M., Lei, Lei, and Ma, Zhenzhen (2019) Chemical compositions and distribution characteristics of cements in longmaxi formation shales, Southwest China. Journal of Earth Science, 30 (5). pp. 879-892.

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Abstract

Shale gas resources have been regarded as a viable energy source, and it is of great significance to characterize the shale composition of different cements, such as quartz and dolomite. In this research, chemical analysis and the multifractal method have been used to study the mineral compositions and petrophysical structures of cements in shale samples from the Longmaxi Formation, China. X-ray diffraction, electron microprobe, field emission scanning electron microscopy, cathodoluminescence microscopy and C-O isotope analyses confirmed that cements in the Longmaxi Formation shales are mainly composed of Fe-bearing dolomite and quartz. Fe-bearing dolomite cements concentrate around dolomite as annuli, filling micron-sized inorganic primary pores. Quartz cements in the form of nanoparicles fill primary inter-crystalline pores among clay minerals. Theoretical calculation shows that the Fe-bearing dolomite cements formed slightly earlier than the quartz cements, but both were related to diagenetic illitization of smectite. Moreover, multifractal analysis reveals that the quartz cements are more irregularly distributed in pores than the Fe-bearing dolomite cements. These results suggest that the plugging effect of the quartz cements on the primary inoraganic pore structures is the dominant factor resulting in low interconnected porosity of shales, which are unfavorable for the enrichment of shale gas.

Item ID: 60928
Item Type: Article (Research - C1)
ISSN: 1674-487X
Keywords: cement, pore structure, multifractal, shale gas reservoir, petroleum geology
Copyright Information: © China University of Geosciences (Wuhan) and Springer-Verlag GmbH Germany, Part of Springer Nature 2019.
Funders: National Key Technology R&D Program of China (NKTP), Natural Science Foundation of China (NSFC), Fundamental Research Funds for the Central Universities, China (CHD)
Projects and Grants: NKTP Grant No. 2016YFC0600501, NSFC 41572315, NSFC 41872250, CHD No. CUG170104
Date Deposited: 13 Nov 2019 07:35
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040309 Petroleum and Coal Geology @ 100%
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