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Carbonate cementation patterns, potential mass transfer, and implications for reservoir heterogeneity in Eocene tight-oil sandstones, Dongying Depression, Bohai Bay basin, China; evidence from petrology, geochemistry, and numerical modeling

Ma Benben, Cao Yingchang, Kenneth A. Eriksson and Wang Yanzhong
Carbonate cementation patterns, potential mass transfer, and implications for reservoir heterogeneity in Eocene tight-oil sandstones, Dongying Depression, Bohai Bay basin, China; evidence from petrology, geochemistry, and numerical modeling
AAPG Bulletin (December 2019) 103 (12): 3035-3067

Abstract

This paper investigates transport mechanisms involving carbonate cementation in Eocene, tight-oil sandstones in Bohai Bay Basin, China, to determine potential mass transfer between adjacent mudstones and sandstones. Evidence from petrology, geochemistry and numerical modeling suggests two generations of carbonate cementation: 1) early non-ferroan calcite (formed at 28-41 degrees C) and dolomite (formed at 45-63 degrees C); 2) later ferroan calcite (formed at 105-124 degrees C) and ankerite (formed at 101-137 degrees C). Based on a 1-D model for a coupled sandstone-mudstone system under low and high temperatures, different distribution patterns of carbonate cements reflect episodic concentration gradients that led to diffusive transport of bicarbonate species during progressive burial. Firstly, extensive precipitation of early non-ferroan calcite followed by dolomite at or near mudstone-sandstone contacts resulted from initial concentration gradients related to different compositions in primary mineral assemblages. Secondly, introduction of aqeous CO (sub 2) from adjacent mudstones into sandstones resulted in dissolution of early non-ferroan carbonates and led to diffusive transport of bicarbonate species. These bicarbonate species were incorporated with Fe (super 2+) and subsequently re-precipitated as ferroan carbonate minerals at distances greater than 2 m from sandstone-mudstone contacts. Therefore, short-distance diffusive transport is inferred to have been the predominant transport mechanism associated with carbonate cementation. Large-scale mass transfer between sandstones and adjacent mudstones occurred in a relatively open geochemical system on a very local scale. Numerical model results show that low porosity zones (2.6% to 5.1%) exhibit coherence with high abundances of carbonate cements (13.9% to 21.2%). Tightly cemented intervals were created by different generations of carbonate cementation and resulted in destruction of sandstone reservoir porosity.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 103
Serial Issue: 12
Title: Carbonate cementation patterns, potential mass transfer, and implications for reservoir heterogeneity in Eocene tight-oil sandstones, Dongying Depression, Bohai Bay basin, China; evidence from petrology, geochemistry, and numerical modeling
Affiliation: China University of Geosciences, Laboratory of Tectonics and Petroleum Resources, Wuhan, China
Pages: 3035-3067
Published: 201912
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 69
Accession Number: 2019-089025
Categories: Isotope geochemistryEconomic geology, geology of energy sourcesSedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. chart, sect., strat. cols., 5 tables, sketch map
N37°00'00" - N39°00'00", E117°00'00" - E119°00'00"
Secondary Affiliation: China University of Petroleum, CHN, ChinaVirginia Polytechnic Institute and State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 2019
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