Facies controls on the distribution of diagenetic alterations in fan delta deposits: a case study from the Lower Cretaceous sandstone, Chagan Sag, Inner Mongolia, China. (5th April 2016)

• Record Type: Journal Article
• Authors: Wei, W.; Zhu, Xiaomin; Tan, Mingxuan; Wu, Chenbingjie; Guo, Dianbin; Su, Hui; Jiang, Feihu
• Is Part Of: Geological journal. Volume 52:Number 4(2017)
• Page Start: 539
• Page End: 558
• Publication Date: 2016-04-05
• Subjects: diagenesis -- fan delta -- reservoir quality -- Chagan Sag -- continental rift basin -- China; Geology -- Periodicals; 551
• DOI: 10.1002/gj.2788
• Languages: English
• ISSNs: 0072-1050

Abstract

Abstract: By integrating diagenesis and sedimentary facies, the distribution of diagenetic alterations and their impacts on reservoir quality were investigated within a lacustrine fan delta depositional environment in the Lower Cretaceous of the Western sub‐sag in the Chagan Sag, Yin‐E Basin, northern China. Core observation and analyses of petrography and geochemistry of the sandstones revealed that the eogenetic alterations display spatial and temporal distribution patterns associated with sedimentary facies, including distributary channels of a fan delta front (DC), distributary bays (DB) and sheet sands (SS) and mouth bar (MB) (SS and MB are collectively referred to as S). Percolation of meteoric waters occurring in high permeability DC sandstones resulted in leaching of feldspar, the formation of kaolinite, as well as mechanical infiltrated clays around detrital grains. Conversely, the DB deposits containing abundant ductile lithic fragments were subjected to mechanical compaction and thus the development of a pseudomatrix. During a long burial residence time (the Early Cretaceous period) in a lacustrine environment, abundant early carbonate cements were precipitated, especially in the distal S sandstones. The sandstones lacking eogenetic cements were subjected to stronger mechanical compaction. Additionally, eogenetic alterations have an important impact on the distribution of the mesogenetic alterations. Sandstones containing few eogenetic cements or thin or discontinuous infiltrated clay rims around the detrital grains were subjected to quartz cementation. However, during the hydrocarbon generation stage, the most efficient percolation of meteoric waters and organic acid dissolved feldspar minerals and carbonate cements, resulted in DC sandstones having more intragranular and intergranular porosity. Owing to high matrix contents and early calcite cement contents, the DB and S sandstones had lower permeability and were rarely dissolved. During the late mesogenetic stage, late carbonate cements occurred in all sedimentary facies and iron and magnesium ions were released from the transformation from kaolinite to illite or to chlorite. The results from this study show possible diagenetic evolutionary pathways in the reservoir sandstones within the fan delta depositional environment, which in turn provides some insights into the controls on reservoir potential. Copyright © 2016 John Wiley & Sons, Ltd.