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通过岩石学、矿物学和地球化学等多学科交叉渗透的方法,来阐明不同期次碳酸盐胶结物的成因机理、分布规律和主控因素及其产生的储层效应。研究表明鄂尔多斯盆地中部延长组砂岩中,碳酸盐胶结物可分为早、中、晚3期,以早期和晚期为主。早期碳酸盐胶结物是在常温常压条件下,直接从过饱和的碱性湖水介质中析出的产物。而中晚期碳酸盐胶结物主要为含(亚)铁方解石,多形成于晚成岩阶段A2期,与碱性成岩流体中发生的水—岩相互作用关系密切。早期碳酸盐胶结物中碳主要来源于大气水中溶解的CO2和湖相原生碳酸盐岩的碳,而中晚期碳酸盐胶结物中,部分同位素组成较轻的碳可能受到有机碳影响;有机酸引起的长石类骨架颗粒溶解为中晚期碳酸盐胶结物形成提供了主要的钙源。不同期次碳酸盐胶结物空间分布具有一定规律性,主要表现在半深湖相中碳酸盐的碳、氧同位素组成相对较重,主要为无机碳,多为早期碳酸盐;而砂质碎屑流、三角洲前缘和三角洲平原相的碳酸盐多为中晚期胶结物,为碱性成岩环境的产物。在其形成过程中存在有机碳的混入,并且随着离湖中心距离的增大,有机碳混入的比例也随之增大。
By means of multi-disciplinary cross-infiltration methods such as petrology, mineralogy and geochemistry, the mechanism of formation, distribution, main controlling factors and reservoir effects of carbonate cements at different stages are clarified. The results show that carbonate cements can be divided into early, middle and late phases in the Yanchang Formation sandstone in the central Ordos Basin, mainly in the early and late stages. Early carbonate cements are products precipitated directly from supersaturated alkaline lake media at ambient temperature and pressure. However, the carbonate cements in the middle and late stages are mostly calcite containing (sub) iron, which formed mostly in the stage A2 of late diagenesis, which is closely related to the water-rock interaction occurring in alkaline diagenetic fluids. Carbon in early carbonate cements comes mainly from carbon dioxide dissolved in atmospheric water and carbon in lacustrine primary carbonate rocks. In the late carbonate cements, some carbons with lighter isotopic compositions may be affected by organic carbon. The dissolution of feldspar skeleton by organic acids provides the main calcium source for the formation of carbonate cements in the late stage. The spatial distribution of carbonate cements has certain regularity in different periods, mainly showing that the carbon and oxygen isotopic compositions of carbonate in the semi-deep lacustrine facies are relatively heavy, mainly inorganic carbon and mostly early carbonates; while the sand Most of the debris in the debris flow, delta front and delta plain are cements, which are products of alkaline diagenetic environments. In the process of its formation, there is the incorporation of organic carbon, and as the distance from the center of the lake increases, the proportion of organic carbon mixed with it increases.