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近年来,柴达木盆地柴西地区始新统致密油勘探取得了重要进展,其主要岩石类型为混积的湖相碳酸盐岩,其中白云石化岩类为最优质的储集岩。通过系统的岩石学、结构学以及地球化学特征研究发现,白云岩以泥晶结构为主,发育少量藻云岩,具有“中孔—特低渗”型的物性特征,孔隙类型以晶间孔为主,含少量溶蚀孔。电子探针能谱面扫描分析结果显示,藻云岩中Mg元素富集区与藻纹层分布高度吻合显示其为微生物成因的原生白云岩,因微生物活动能够克服动力学障碍,为白云石形成营造出有利的微环境;偏光显微镜观察和X射线衍射分析结果显示,泥晶白云岩中均含碎屑颗粒和泥质组分,因周缘辫状三角洲沉积带来的碎屑物质混积而成,电子探针岩石组分分析结果显示其具有“高铝硅低铁锰”特征,Fe O的平均含量为0.942%,Mn O的平均含量为0.052%,明显低于文献报道的热液成因的白云岩中的铁锰含量,为准同生交代成因的典型特征。白云石化过程中产生了大量弥散性收缩晶间孔,孔隙半径小而数量众多是其孔隙度较高而渗透率较低的主要原因,这一发现对于柴达木盆地始新统的致密碳酸盐岩油气勘探具有重要意义。
In recent years, significant progress has been made in the Eocene tight oil exploration in Chaixi area of the Qaidam Basin. The main types of rocks are lacustrine carbonate rocks, and the dolomitization rocks are the highest quality reservoir rocks. Based on the systematic petrology, structural and geochemical characteristics, it is found that dolomite is dominated by a muddy crystalline structure with a small amount of algal dolomite, possessing the physical characteristics of “mesopore-ultra-low permeability” type and pore type of crystallite Between the main hole, with a small amount of dissolution hole. Scanning electron spectroscopy spectrum analysis showed that algal dolomites in the enrichment zone of Mg and algal stratigraphic distribution of highly consistent shows that it is a microbial genesis of the original dolomite due to microbial activity can overcome the kinetic obstacles for dolomite formation The results of polarization microscope and X-ray diffraction analysis show that the dolomitic dolomite contains detrital particles and muddy components, which are caused by the mixture of detrital material caused by the deposition of the peripheral braided delta The results of the rock component analysis of the electron probe show that it has the characteristics of high Al, Si, Fe, Mn and Fe, the average content of Fe 0 is 0.942% and the average content of Mn O is 0.052%, which is obviously lower than that reported in the literature The origin of dolomite in the iron and manganese content, quasi-synonymous genesis of the typical characteristics. During the dolomitization process, a large number of dispersive shrinkage intergranular pores are generated. The small pore radius and large number are the main reasons for the higher porosity and lower permeability. This finding is of great significance for the tight carbonate Salt rock oil and gas exploration is of great significance.