Diagenetic evolution and reservoir quality of the Oligocene sandstones in the Baiyun Sag, Pearl River Mouth Basin, South China Sea  

作　　者：Bing Tian Shanshan Zuo Youwei Zheng Jie Zhang Jiayu Du Jun Tang 

机构地区：[1]Institute of Mining and Coal,Inner Mongolia University of Science and Technology,Baotou 014010,China [2]Institute of Science,Inner Mongolia University of Science and Technology,Baotou 014010,China

出　　处：《Acta Oceanologica Sinica》2024年第2期67-82,共16页海洋学报（英文版）

基　　金：The National Natural Science Foundation of China under contract No. 42262020;the Research Program of Science and Technology at Universities of Inner Mongolia Autonomous Region under contract No. NJZY22445。

摘　　要：The Oligocene Zhuhai sandstones are significant reservoirs for hydrocarbons in the Baiyun Sag, South China Sea.For effective appraisal, exploration and exploitation of such a deep-water hydrocarbon sandstone, samples of five wells from depths of 850 m to 3 000 m were studied. A series of comprehensive petrographic and geochemical analyses were performed to unravel the diagenetic features and their impact on the reservoir quality.Petrographically, the sandstones are dominated by feldspathic litharenites and lithic arenites with fine to medium grain sizes and moderate to good sorting. The reservoir quality varies greatly with a range of porosity from 0.2% to 36.1% and permeability from 0.016 ×10~(–3) μm~2 to 4 301 ×10~(–3) μm~2, which is attributed to complex diagenetic evolution related to sedimentary facies;these include compaction, cementation of calcite, dolomite, siderite and framboidal pyrite in eogenetic stage;further compaction, feldspar dissolution, precipitation of ferrocalcite and ankerite, quartz cements, formation of kaolinite and its illitization, precipitation of albite and nodular pyrite, as well as hydrocarbon charge in mesogenetic stage. The dissolution of feldspar and illitization of kaolinite provide internal sources for the precipitation of quartz cement, while carbonate cements are derived from external sources related to interbedded mudstones and deep fluid. Compaction is the predominant factor in reducing the total porosity, followed by carbonate cementation that leads to strong heterogeneity. Feldspar dissolution and concomitant quartz and clay cementation barely changes the porosity but significantly reduces the permeability.The high-quality reservoirs can be concluded as medium-grained sandstones lying in the central parts of thick underwater distributary channel sandbodies(>2 m) with a high content of detrital quartz but low cement.

关 键 词：Baiyun Sag OLIGOCENE Zhuhai Formation DIAGENESIS reservoir quality 

分 类 号：P618.13[天文地球—矿床学]