Diagenesis is one of the most predominant factors controlling reservoir quality in the deeply buried siliciclastic sandstones of the third member in the Eocene Shahejie Formation (Es₃), in the Raoyang Sag, the Bohai Bay Basin. In this study, thin section, cathodoluminescence (CL), scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectrum, carbon and oxygen isotopes, and fluid inclusion analyses are used to restructure paragenetic sequences and detect origins of carbonate cements recorded in this deeply buried member. Based on petrographic analyses, the Es₃ sandstones are identified as lithic arkoses and feldspathic litharenites at present, but derived from original arkoses and lithic arkoses, respectively. Geohistorically, the Es₃ sandstones have undergone two diagenetic episodes of eogenesis and mesogenesis. Events observed during eogenesis include chemical compaction, leaching of feldspar, development of chlorite coating and kaolinite, precipitation of the first generation of quartz overgrowth (QogI), dissolution of feldspar, and precipitation of calcite and nonferroan dolomite cement. Mesogenetic alterations include chemical compaction, precipitation of kaolinite aggregate and the second generation of quartz overgrowth (QogII), precipitation of ankerite, development of I/S and illite, and formation of pyrite. Carbon and oxygen isotopic data show that calcite cements are characterized by ¹³C ( ranging from -0.7‰ to 1.0‰ with an average of 0.1‰) and ¹⁸O ( varying from 12.3‰ to 19.0‰ with an average of 16.2‰); these stable isotopic data combined with value (from 114.69 to 122.18) indicate skeletal debris ( ranging from -1.2‰ to -1.1‰ with an average of -1.15‰; varying from 23.0‰ to 23.2‰ with an average of 23.1‰) and ooids in adjacent carbonate beds involved in meteoric water and seawater from outside jointly served as the carbon sources. For nonferroan dolomite, the value of -4.1‰ is a little bit negative than the calcite, and the of 14.3‰ is coincident with the calcite, which suggest the nonferroan dolomites come from the diagenetic fluids with a similar oxygen isotopic composition to that of the calcite but modified by the external acidic ¹³C-depleted water. However, the ankerites are actually rich in ¹²C ( ranging from -10.0‰ to -1.2‰, ) and ¹⁶O ( varying from 10.1‰ to 19.4‰, ), when combined with the distribution of cutting down along the direction pointing to sand-body center from the margin and microthermometric temperature (Th’s) data mainly varying between 115.2°C and 135.5°C with an average of 96.0°C, indicating the main origination from the Es₃ source rocks with effective feldspar buffer action for the acidic fluids in the margins of the Es₃ sandstones. In addition, the necessary elements for ankerite such as Fe²⁺, Ca²⁺, and Mg²⁺ ions also come from organic matter and clay minerals during thermal maturation of the Es₃ source rocks. The study provides insights into diagenetic processes and origination of carbonate cements in the Es₃ sandstones; it will facilitate the cognition of predictive models of deeply buried sandstone reservoirs to some extent, which can reduce the risks involved in oil and gas exploration and development.

中文翻译：

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渤海湾盆地饶阳凹陷始新统Es3段深埋砂岩中碳酸盐胶结物成岩与成因

成岩作用是控制渤海湾盆地饶阳凹陷始新世第三系（Es ₃）深部硅质碎屑砂岩储层质量的最主要因素之一。在这项研究中，薄截面，阴极发光（CL），扫描电子显微镜（SEM），X射线衍射（XRD），拉曼光谱，碳和氧同位素以及流体包裹体分析被用于重构共生序列并检测碳酸盐的成因。在这个深埋的成员中记录的水泥。根据岩相学分析，Es ₃砂岩目前被确定为岩质长石和长石斜长石，但分别来自原始的岩质和岩性长石。从地理角度来看，ES ₃砂岩经历了成岩作用和成岩作用两个成岩作用。在发生过程中观察到的事件包括化学致密化，长石的浸出，绿泥石涂层和高岭石的形成，第一代石英过度生长（QogI）的沉淀，长石的溶解以及方解石和非铁白云石水泥的沉淀。介晶改变包括化学致密化，高岭石聚集体的沉淀和第二代石英长生（QogII），铁矿的沉淀，I / S和伊利石的发展以及黄铁矿的形成。碳氧同位素数据表明，方解石水泥的特征为¹³ C（范围为-0.7‰至1.0‰，平均为0.1‰）和¹⁸ O（从12.3‰到19.0‰不等，平均为16.2‰）; 这些稳定的同位素数据加上值（从114.69至122.18）表明骨骼碎片（从-1.2‰至-1.1‰，平均为-1.15‰；从23.0‰至23.2‰，平均为23.1‰）和卵石在相邻的碳酸盐岩层中，大气层和海水均来自外部，共同作为碳源。对于非铁白云岩，-4.1‰的值比方解石稍负，而14.3‰的值与方解石一致，这表明非铁白云石来自与氧同位素组成相似的成岩流体。方解石，但经外部酸性¹³改性贫C水。然而，铁包石实际上富含¹² C（从-10.0‰到-1.2‰，）和¹⁶ O（从10.1‰至19.4‰，），结合从边缘和微热温度（Th's）沿指向砂体中心的方向的切分分布，数据主要在115.2°C和135.5°C之间变化，平均96.0°C，表明源自Es ₃烃源岩，对Es ₃砂岩边缘的酸性流体具有有效的长石缓冲作用。此外，在Es ₃烃源岩的热成熟过程中，铁素体的必需元素，如Fe 2 ⁺，Ca ²⁺和Mg ²⁺离子也来自有机物和粘土矿物。该研究提供了对ES中碳酸盐胶结物成岩过程和成因的见解。_3个砂岩；它将在一定程度上促进对深埋砂岩储层预测模型的认识，从而可以减少涉及油气勘探开发的风险。