Chemical Compositions and Distribution Characteristics of Cements in Longmaxi Formation Shales, Southwest China

作     者：Wenda Zhou Shuyun Xie Zhengyu Bao Emmanuel John M. Carranza Lei Lei Zhenzhen Ma 

作者机构：State Key Laboratory of Geological Processes and Mineral Resources (GPMR) School of Earth Sciences China University of Geosciences Wuhan 430074 China Faculty of Chemistry and Material Sciences China University of Geosciences Wuhan 430074 China Geological Sciences School of Agricultural Earth and Environmental Sciences University of KwaZulu-Natal Westville 3629 South Africa Economic Geology Research Centre (EGRU) James Cook University Townsville QLD 4811 Australia 

出 版 物：《Journal of Earth Science》 (地球科学学刊（英文版）)

年 卷 期：2019年第30卷第5期

页      面：879-892页

核心收录：

学科分类：07[理学] 0708[理学-地球物理学] 0704[理学-天文学] 

基　　金：financially funded by the National Key R&D Program of China(No.2016YFC0600501) the Natural Science Foundation of China(Nos.41572315,41872250) the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(No.CUG170104) 

主　　题：cement pore structure multifractal shale gas reservoir petroleum geology 

摘      要：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.