【作者】 裴昌蓉；

【导师】 黄思静；

【作者基本信息】 成都理工大学 ， 矿物学、岩石学、矿床学， 2007， 硕士

【摘要】 论文运用阴极发光、扫描电子显微镜、偏光显微镜和化学分析等手段，对西湖凹陷中南部古近系砂岩储层中自生碳酸盐矿物的矿物学、岩石学、地球化学特征进行了综合分析，评价了碳酸盐胶结物对储层的影响，探讨了碳酸盐胶结物的形成机制。碳酸盐是西湖凹陷中南部古近系储层砂岩中含量最多的自生矿物类型，高岭石次之。西湖凹陷古近系自生碳酸盐矿物包括方解石、铁白云石和菱铁矿三种主要类型。岩石中方解石胶结物的含量越高，其δ¹³C越低，与有机酸的关系越密切；同时，连生方解石胶结物具最低的δ¹⁸O值，说明其形成温度较高，形成时间也相对较晚。铁白云石δ¹⁸O平均值比连生方解石胶结物高6.4‰，说明铁白云石的形成温度相对较低，形成时间相对较早。铁白云石胶结物的δ¹³C值（平均值-2.8‰）显著高于连生方解石胶结物，并更靠近0‰的海相碳酸盐的δ¹³C值，其物质来源与海相碳酸盐有关，同时有大气CO₂参与。在压实作用和胶结作用两个影响孔隙度的主要成岩因素中，压实作用是造成西湖凹陷古近系砂岩孔隙度降低的第一重要因素。对具连生方解石胶结物的岩石和具粒状环边铁白云石的岩石作胶结物含量—负胶结物孔隙度投点图，结果表明胶结作用是降低这些岩石孔隙度的第一重要因素。连生方解石胶结物封堵粒间孔隙；铁白云石的自形晶体以及较小的分子体积使得白云石的晶体之间总是存在较多的次生孔隙，同时早期的铁白云石胶结作用同样会显著提高岩石的机械强度和抗压实能力，使以后岩石免遭进一步较强的压实作用。少数具有很大的粒间孔隙体积的连生方解石是在岩石尚未经历有效压实作用的较早成岩阶段形成的，其形成机制与（铝）硅酸盐矿物的水化作用有关；大多数存在于高负胶结物孔隙度岩石中的连生方解石胶结物是在有机物演化到大量羧酸形成、长石广泛溶解之后的埋藏成岩阶段形成的。大气水的溶解作用造成以颗粒环边或孔隙衬里方式产出的铁白云石胶结物的沉淀作用在相对早期的成岩阶段发生，其物质来源中存在海源碳酸盐物质。菱铁矿主要是同生或准同生阶段沉淀（或沉积）成因的（一些粉晶菱铁矿可能是早成岩阶段的胶结物）。更多还原

【Abstract】 By means of thin-section analysis, cathodeluminecenme analysis, element analysis, isotope analysis and SEM examination, authigenic carbonate mineral in the early Tertiary sandstone of south-central XiHu depression was studied here. Based on those experiments, the petrology character, mineral character and geochemistry character of authigenic carbonate mineral is analysed, the effect on the reservoir quality for carbonate cements is evaluated, and its formation mechanism is discussed.Carbonate is the most abundant authigenic mineral in the early Tertiary sandstone of south-central XiHu depression, kaolinite secondly. The authigenic carbonate mineral mainly consists of calcite, ankerite and siderite. The higher amount of calcite cement, the lowerδ¹³C value, and the closer relationship with organic acid. Meantime, with lowerδ¹⁸O value, the formation temperature of mosaic calcite is higher, and the formation time is later. Theδ¹⁸O mean value for ankerite is 6.4‰higher than mosaic calcite, means that the the formation temperature of ankerite is lower, and its formation time is earlier. Theδ¹³C value for ankerite cement （mean value is -2.8%o） is higher than mosaic calcite cement visibly, and nearby theδ¹³C value of marine carbonate（0‰）, that is to say, the material resource for ankerite cement is from marine carbonate and meteoric CO₂ partly.Compaction processes and cementation, as the two most important diagenesis effect factors on reduction the porosity, are judged here, and showed that compaction processes is more important for the reservoir sandstone on reduction porosity than cementation. With a graph of intergranular volume vs. cement assessed, the rocks, which are cemented by calcite or ankerite, is caused by cementation predominantly on its porosity reduction. Calcite cement occludes intergranular volume; the ankerite formed early stage with more secondly porosity can improve the mechanical strength and anti-compact power for rocks, and stick up to the futher compaction later.Little mosaic calcite with more intergranular volume is formed in the early diagenesis stage when the rocks did not compact effectively, and its formation mechanism is connected with the hydration of aluminosilicate; most mosaic calcite cement with high minus cement porosity is formed in the burial diagenesis stage when organic material developed extensively carboxylic acid and feldspar dissoluted widely. The ankerite cement deposited on early diagenesis stage with meteoric fluids dissolution, and partly came from marine carbonate material perhaps. Siderite deposited on iyngenesis stage.更多还原