Meteoric Leaching Evidences, Diagenetic Model and Its Geology Significance in Mixed Rock of Steep Slope Zone of Shijiutuo Uplift
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摘要: 石臼坨凸起陡坡带Q29和Q36构造中深部储层是渤海最大的湖相碳酸盐岩和扇三角洲碎屑岩的混合沉积，这一亿吨级油气田的发现，刷新了碎屑岩储层最厚、单层油层最厚、测试产能最高纪录.通过岩心观察、薄片鉴定、碳氧同位素分析、元素分析等多种分析手段，认为同沉积大气水淋滤作用，对石臼坨凸起陡坡带混积岩系优质储层的形成起到了至关重要的影响.通过对岩石学标志和元素地球化学标志的分析认为，大气水淋滤作用的主要包括两个过程，一是同沉积淋滤作用下，砾石段产生的选择性溶蚀孔、粒内缝、碎屑高岭石；二是沉积后暴露下，碳酸盐岩段产生的垂直岩溶缝、悬垂状白云石、示顶底构造.在此基础上，提出了大气水淋滤作用的模式，可分为成岩作用差异明显两个成岩带，即大气水渗流带和大气水潜流带，并进一步总结了各带内部的成岩特征和演化模式.Abstract: QHD29-2E and Q36 structure is so far the largest fan delta siliciclastic and lacustrine carbonate mixed deposits in the first and second members of Shahejie Formation in Paleogene system of Bohai Bay area,which breaks record of maximum reserve scale of siliclastic-carbonate mixed reservoir,the maximum thickness of single oil-bearing layer,and the highest tested productivity in Bohai Sea area. In our recent research,based on comprehensive analysis of rock core,rock slice observation,carbon and oxygen isotope analysis and trace element analysis,it is found that meteoric water leaching diagenesis is the major factor for high reservoir quality forming in the mixing deposition of steep slope zone of Shijiutuo uplift. Petrographical and geochemical evidences of meteoric waters process are identified. It includes 2 processes:dissolution pores,integranular fissures,terrigenous kaolinite in conglomerates during syndepositional process,and vertical karst fissures,geopetal structure in carbonates during subaerial exposure. The meteoric leaching process could be divided into 3 stages,including provenance,transportation and beach bar periods. Finally,the meteoric diagenetic model of mixed deposits in the slope zone is established. Meteoric diagenesis takes place primarily in two formation zones:the vadose zone and the phreatic zone. The diagenetic feature and evolution model of each zone are also concluded.
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图 2 岩石类型和孔隙类型
a.Q36-2井，鲕粒原生孔，3 779.50 m，单偏光；b.Q36-2井，生物体腔孔，3 765.43 m，单偏光；c.Q36-2井，选择性溶蚀，保留泥晶套，3 766.23 m，单偏光；d.Q36-2井，溶蚀粒间孔，3 779.58 m，单偏光；e.Q29-E5井，原生粒间孔发育，3 425.00 m，单偏光；f.Q29-E5井，白云质细-中砾岩，3 373.75 m，单偏光；g.Q29-E5井，砾岩微裂缝，3 445.00 m，单偏光；h.Q29-E5井，白云质表鲕状不等粒砂质细砾岩，3 371.00 m，单偏光
Fig. 2. Rock types and pore types
图 3 石臼坨凸起陡坡带储层物性特征
a.孔隙度(%)随着深度变化散点图；b.渗透率(10-3 μm2)随着深度变化散点图
Fig. 3. Reservoir physical properties in steep slope zone in Shijiutuo uplift
图 4 大气水淋滤作用识别标志
a.Q29-E5井，白云质不等粒砂质细砾岩，中酸性岩屑溶蚀，3 672.00 m，50-，铸体薄片；b.Q29-E5井，白云质细-中砾岩，流纹质选择性溶蚀，3 375.18 m，50-，铸体薄片；c.Q29-E5井，矿物选择性溶蚀形成的铸模孔，3 375.37 m，50-，铸体薄片；d.Q29-E5井，粒内缝，3 445.00 m，50-，铸体薄片；e.Q29-E5井，扩大的粒内缝，3 378.36 m，100-，铸体薄片；f.Q29-E5井，再次扩大的粒内缝(几乎变成铸模孔)，3 378.36 m，100-，铸体薄片；g.Q29-E5井，充填粒间同沉积高岭石，3 445.00 m，40，岩心；h.Q29-E5井，环边和充填裂缝同沉积高岭石，3 378.36 m，100-，铸体薄片，岩心；i.Q29-E5井，碎屑状高岭石，3 378.36 m，100-，扫描电镜；j.Q36-2井，3 772.03~3 772.23 m，垂直岩溶缝，未充填，岩心；k.Q29-E5井，3 375.40~3 375.60 m，垂直岩溶缝，白云石充填，岩心；l.Q2E-5井, 3 372.18 m；m.Q29-E5井，3 385.03 m，25+，示顶底构造，普通薄片；n.Q29-E5井，3 382.35 m，悬垂状白云石胶结，普通薄片；o.Q29-E5井，3 382.34 m，悬垂状方解石胶结，普通薄片
Fig. 4. Identification of meteoric water leaching
图 5 碳酸盐岩δ13C-δ18O(PDB标准)成因图解
Fig. 5. Diagenetic genesis of carbonate rocks δ13C-δ18O (PDB standard)
图 6 石臼坨凸起陡坡带沙一、二段微量元素变化
Fig. 6. Trace element analysis in the first and second members of Shijiutuo uplift
图 7 石臼坨凸起大气水淋滤作用成岩模式
Fig. 7. Meteoric water leaching and diagenetic model in Shijiutuo uplift
图 8 扇根砂砾岩和滩相砂砾岩对比
a.Q29-E4井3 348.34 m，25-；b.Q29-5井3 384.28 m，25-；c.孔隙度渗透率交会图；d.Q29-E4井3 348.10~3 348.34 m；e.Q29-5井3 383.10~3 383.34 m
Fig. 8. Comparison of glutenite in fan root and beach facies
表 1 同位素温度数据和计算结果
Table 1. Isotopic temperature data and calculation results
井号 深度(m) 岩石/矿物 δ13C δ18O Z值 温度(℃) (PDB, ‰) (PDB, ‰) SMOW(‰) Q29-E5 3 340.78 泥晶白云石Ⅰ 2.33 -6.95 23.755 106 128.610 7 38.22 3 340.78 亮晶包壳Ⅰ 2.67 -6.36 24.363 349 129.600 9 35.46 3 380.25 亮晶包壳Ⅰ 2.02 -4.97 25.796 328 128.961 9 29.24 3 775.06 粒间胶结物Ⅰ 1.88 -4.01 26.786 011 129.153 3 25.15 3 341.25 亮晶包壳Ⅰ 4.59 -5.58 25.167 466 133.921 5 31.92 3 382.10 栉壳环边Ⅰ 4.70 -0.76 30.136 501 136.547 1 28.38 3 775.06 泥晶白云石Ⅱ 0.29 -6.97 23.734 488 124.422 9 48.29 3 775.06 泥晶白云石Ⅱ 0.15 -6.24 24.487 059 124.499 7 44.54 3 376.50 孔隙衬垫Ⅱ 0.32 -5.82 23.920 046 125.057 0 42.44 3 375.65 粒间胶结物Ⅱ 0.65 -5.64 25.105 611 125.822 5 41.56 
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