摘要
为明确咸化湖盆碎屑岩储层胶结物类型,探究水体盐度对胶结强度的控制作用,以柴达木盆地古近系为例,通过偏光显微镜进行铸体薄片鉴定及全岩矿物、黏土矿物、阴极发光、扫描电镜、微量元素等实验测试分析,对盆地胶结物类型、湖盆水体古盐度对胶结物类型及胶结强度的控制作用等方面进行研究,建立碳酸盐、硬石膏胶结物总量与古盐度之间的相关关系公式.结果表明:柴达木古近系咸化湖盆发育方解石、白云石、硬石膏、方沸石、石英次生加大及长石次生加大6 种胶结类型,明确硬石膏、方解石胶结成因机制;提出碳酸盐与硬石膏胶结物的分布受水体古盐度控制,靠近盐湖中心以硬石膏胶结为主,向湖盆边缘过渡为方解石与硬石膏胶结、方解石胶结,且胶结强度减弱、胶结物含量降低;指出盐度小于 9‰时以碳酸盐胶结为主,盐度在 9‰～15‰时为碳酸盐和硬石膏胶结,盐度大于15‰时为硬石膏胶结;湖盆水体古盐度每增加1.0‰,胶结物总量平均增加大于0.5%,离盐湖中心距离增加1.0 km,胶结物总量减少 0.68%.
Abstract
To clarify the types of cement in clastic reservoirs of saline lake basins and explore the controlling effect of water salinity on cement strength,we use the Paleogene of the Qaidam Basin as a case study.Experimental tests and analyses,such as casting thin-section,whole rock minerals,clay minerals,cathodoluminescence,and scanning electron microscopy,trace elements,were conducted.The study investigated the types of cement in the basin and the influence of ancient water salinity on cement types and strength,establishing a correlation formula between the total amount of carbonate and anhydrite cement and ancient salinity.The results indicate that six types of cement materials,including calcite,dolomite,anhydrite,zeolite,quartz overgrowth,and feldspar overgrowth,developed in the saline lake Basin of the Qaidam Paleogene,shedding light on the formation mechanism of anhydrite and calcite cementation.The distribution of carbonate and anhydrite cement is controlled by the paleosalinity of the water body.Anhydrite cement is dominant near the salt lake center,while calcite and anhydrite transition toward the basin's edge,with decreasing bonding strength and reduced cement content.The study iden-tifies key salinity thresholds:below 9‰,carbonate cementation dominates;between 9‰ and 15‰,both carbonate and an-hydrite cementation occur;above 15‰,anhydrite cementation prevails.Additionally,for every 1.0‰ increase in paleosalin-ity,the average total cement content increases by more than 0.5%,while for every 1.0 km increase in distance from the lake center,the cement content decreases by 0.68% .
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