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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
DOI: 10.1306/08232221122
Sedimentary and diagenetic archive of a deeply buried, upper Ediacaran microbialite reservoir, southwestern China
Yongjie Hu,1 Chunfang Cai,2 Ying Li,3 Dawei Liu,4 Tianyuan Wei,5 Daowei Wang,6 Lei Jiang,7 Rongtu Ma,8 Shuyuan Shi,9 and Adrian Immenhauser10
1Sinopec International Petroleum Exploration and Production Corporation, Beijing, China; Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; [email protected]
2Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China; and Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing, China; [email protected]
3School of Earth Sciences and Engineering, Nanjing University, Nanjing, China; [email protected]
4Sinopec Petroleum Exploration and Production Research Institute, Beijing, China; [email protected]
5Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China; and Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing, China; [email protected]
6School of Energy Resources, China University of Geosciences (Beijing), Beijing, China; [email protected]
7Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing, China; [email protected]
8Sinopec International Petroleum Exploration and Production Corporation, Beijing, China; [email protected]
9PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China; [email protected]
10Ruhr University Bochum, Faculty for Geosciences, Bochum, Germany; Fraunhofer Institution for Energy Infrastructure and Geothermal Systems, Bochum, Germany; [email protected]
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 yield 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 pore water environment at an early diagenetic stage. Maximum porosity (∼4%–6%) and permeability values (∼0.01–10 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, whereas 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 decrease in parallel, whereas the salinity of fluid inclusion in saddle dolomites increases. One-dimensional numerical models support the increase in porosity as a response to meteoric and hydrothermal diagenesis. The data shown here are relevant for those concerned with petroleum exploration in ancient, deeply buried microbialite reservoirs.
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