摘要:碳酸盐胶结物是西湖凹陷平湖组储层砂岩中含量最多，对储层质量影响最大的自生矿物。通过岩心观察、薄片鉴定、阴极发光、元素成分分析及碳氧同位素分析结果表明，西湖凹陷平湖组储层砂岩中碳酸盐胶结物的主要矿物类型是方解石、铁方解石、白云石和铁白云石，偶见菱铁矿。碳酸盐胶结物的碳同位素（δ13C）值分布范围较集中，为-7.80‰～1.40‰，平均值-2.11‰，氧同位素（δ18O）值整体偏负，为-19.26‰～-9.99‰，平均值-13.79‰。据胶结物碳氧同位素分析恢复古盐度Z值及测算古地温判断碳酸盐胶结物的成岩流体主要为淡水水体，存在部分海水的影响；碳主要来自湖相碳酸盐岩溶解的产物和有机质成熟过程中排放的有机酸。不同类型和时期形成的胶结物对储层影响不一，白云石和大部分方解石形成在中成岩B期堵塞喉道，对储层起破坏作用，但成岩早期靠近不整合面受到了大气淡水影响的方解石对储层影响是保持性的；而埋深较浅，形成温度低的铁白云石对储层起建设性作用。
关键词: 平湖组/
煤系地层/
碳酸盐胶结物/
碳氧稳定同位素
Abstract:Carbonate cements are the most abundant authigenic mineral, which had the greatest influence on reservoir quality in Pinghu Formation in Xihu Sag. The results of core observation, thin section analysis, cathodoluminescence, elemental composition and carbon and oxygen isotope analysis showed that the main mineral types of carbonate cements in the reservoir sandstone of Pinghu Formation in Xihu Sag are calcite, ferric calcite, dolomite and ferric dolomite, with siderite occasionally. The δ13CPDB value of carbonate cements is concentrated, ranging from -7.80‰ to 1.40‰, with an average -2.11‰. The δ18OPDB value is generally negative, ranging from -19.26‰ to -9.99‰, with an average -13.79‰. In this study, we recovered the paleosalinity Z value, and calculated the paleogeotemperature by carbon and oxygen isotopic analysis of cements, which showed that the diagenetic fluid of carbonate cements was mainly fresh water, and partly influenced by sea water. Carbon mainly comes from lacustrine carbonate dissolution and organic acids released during the maturation of organic matter. The cements formed in different types and periods have different effects on the reservoirs. The dolomite and most calcite formed in the Stage B of middle diagenesis blocked the throats, damaging the reservoirs. However, the calcite formed in the early diagenesis closed to the unconformable surface affected by atmospheric fresh water has a good influence on the reservoirs. The shallow iron dolomite with lower temperature played a constructive role.
Key words:Pinghu Formation/
Coal measure strata/
Carbonate cement/
Carbon and oxygen stable isotopes
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