Origin of Carbonate Cements in the Overpressured Top Seal and Adjacent Sandstones in Dongying Depression
详细信息
- 责任者：Han Yuanjia (Key Laboratory of Tectonics & Petroleum Resources ; Ministry of Education ; China University of Geosciences ; Wuhan 430074 ; China) ; He Sheng
- 刊名：Acta Petrolei Sinica
- 出版年：2012
- 卷期：33(3)
- 关键词：碳酸盐岩 ; carbonate rocks ; 胶结物 ; cement ; 砂岩储集层 ; sandstone reservoirs ; 东营凹陷 ; Dongying Sag
- 页码：p.385-393
- 图表：5 illus., 2 tables, 29 refs.
- 分类号：1003
- issnNo：ISSN0253-2697
- isbnNo：CN11-2128/TE
摘要
The burial depth of the overpressured top boundary ranges from 2 200～2 800 m in the Dongying Depression.Interacted by overpressured fluids that flow beneath,the overpressured top boundary is generally characterized by well-developed carbonate mineralization,commonly with carbonate content between 15%～40%.The statistical analysis on in-situ electron-microprobe compositional data of 101 carbonate cements from 53 sandstone samples indicated that carbonate minerals could be basically subdivided into three groups,i.e.penecontemporaneous dolomite,calcite and ankerite.Integrated with X-ray diffraction and cathodoluminescence data,their diagenetic sequence was determined as penecontemporaneous dolomite→calcite→ankerite.On the basis of observation of primary inclusions in carbonate cements,the precipitation of carbonate minerals in the overpressured top seal and adjacent sandstones was accompanied with overpressured fluids,with a minimum paleopressure coefficient ranging between 1.29～1.62 and a precipitation temperature obviously higher than the background temperature,which suggested a significant influence by overpressured thermal fluid invasion.Thus,based on previous study results,we proposed that the precipitation of calcite and ankerite cements might be related to activities of overpressured fluids since the deposition at the terminal Dongying stage and the Minghuazhen stage,respectively.Furthermore,this hypothesis was tested by measured oxygen isotopic values that fluctuate from-16.86‰ to-12.29‰ PDB for calcite and from-12.20‰ to-10.20‰ PDB for ankerite.Further investigations suggested that the calcite should precipitate at 90～120℃ for the δ18OSMOW of its homochronous overpressured fluid is around 0.00‰ and the ankerite should precipitate at 110～135℃ for the δ18OSMOW of its homochronous overpressures fluid is 0.25‰.δ13C values of carbonate cements formed at the late diagenesis show a positive shift,ranging from-0.9‰ to +3.58‰,which indicates an origin mainly from the dissolution-reprecipitation process of the Es4 lacustrine carbonate,or an influence of intramolecular carbon isotopic fractionation within carboxylic acids,though the latter seems to play a relatively minor role.
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