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AAPG Bulletin, Preliminary version published online Ahead of Print 1 October 2022.

Copyright © 2022. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/08232221122

Sedimentary and diagenetic archive of a deeply-buried, upper Ediacaran microbialite reservoir, S.W. China

Yongjie Hu12 , Chunfang Cai267 , Ying Li5 , Dawei Liu8 , Tianyuan Wei267 , Daowei Wang9 , Lei Jiang27 , Rongtu Ma1 , Shuyuan Shi10 , and Adrian Immenhauser34

1 Sinopec International Petroleum Exploration and Production Corporation, Beijing 100029, China
2 Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
3 Ruhr University Bochum, Faculty for Geosciences, Bochum, Germany
4 Fraunhofer Institution for Energy Infrastructures and Geothermal Systems (IEG), Bochum, Germany
5 School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
6 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
7 Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing 100029, China
8 Petroleum Exploration and Production Research Institute of SINOPEC, Beijing 102206, China
9 School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China
10 PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China
* Corresponding Author

Ahead of Print Abstract

Some Precambrian carbonate rock bodies host economic petroleum reserves. Here, we present a case study of the deeply-buried (>5 km) upper Ediacaran Dengying Formation (ca 551-541 Ma) to document the formation of a microbialite gas field. Detailed petrological and geochemical data are presented and placed in context with porosity and permeability analyses. This approach leads to a better understanding of Ediacaran microbialite textures, diagenetic pathways, and reservoir properties in general. Microbialite facies yields a positive correlation between sorting coefficient and porosity. Compared with other microbial fabrics, thrombolites have well-connected pore networks and large pore-throat radii. Fibrous dolomite cement was precipitated in a marine porewater environment at an early diagenetic stage. Maximum porosity (~4 to 6%) and permeability values (~0.01 to 10 mD) are established in spatially confined stratigraphic intervals. Meteoric diagenesis correlates with transient subaerial seafloor exposure and affects carbonates. Meteoric diagenesis is typified by dolostone with low δ13C (~−2 to 0‰) and δ18O values (~−11 to −8‰). Silica phases were subsequently precipitated from hydrothermal fluids, while reflux and burial dolomitization increased reservoir performance. In the deep-burial regime, late-stage hydrothermal fluids resulted in the generation of secondary pores. Along hydrothermal pathways, fluid-inclusion temperatures, Sr contents and radiogenic 87Sr/86Sr ratios of saddle dolomite all decrease in parallel, while the salinity of fluid-inclusion in saddle dolomites increases. 1-D numerical models support the increase of porosity as a response to meteoric and hydrothermal diagenesis. Data shown here are relevant for those concerned with petroleum exploration in ancient, deeply-buried microbialite reservoirs.

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Please cite this AAPG Bulletin Ahead of Print article as:

Yongjie Hu , Chunfang Cai , Ying Li , Dawei Liu , Tianyuan Wei , Daowei Wang , Lei Jiang , Rongtu Ma , Shuyuan Shi , Adrian Immenhauser: Sedimentary and diagenetic archive of a deeply-buried, upper Ediacaran microbialite reservoir, S.W. China, (in press; preliminary version published online Ahead of Print 01 October 2022: AAPG Bulletin, DOI:10.1306/08232221122.

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