以鲕粒碳酸盐岩薄片样品为研究对象,通过光学显微镜、扫描电镜(SEM)观察样品在稀硫酸溶液作用下溶蚀前后的微观形貌,并总结溶蚀规律,结合能谱仪(EDS)进行成分分析,在此基础上探讨了碳酸盐岩的溶蚀机理.结果显示,鲕粒碳酸盐岩存在对结构和成分的多重选择性溶蚀.从微观形貌来看,相对于鲕粒灰岩,鲕粒白云岩更易产生连通性较好的溶蚀孔洞,形成有效的储集空间;从反应后(12 h)的溶蚀量来看,鲕粒白云岩的失重百分比为1.04,,亦大于鲕粒灰岩的0.70,.能谱分析发现,成分不均一性亦是控制溶蚀反应进程的关键因素,元素含量差异较大的部位更易发生溶蚀作用.鲕粒白云岩溶蚀区域的Mg/Ca值为0.6～0.8,远远小于未溶蚀区域,表明Mg元素含量高的区域更易溶蚀,进而导致Mg/Ca值降低;鲕粒灰岩Si和Al含量高的区域,不易发生溶蚀,这说明石英和长石等难溶矿物的存在会阻碍溶蚀作用的进行,也阻碍了孔隙空间的形成.根据实验结果推测,鲕粒白云岩在含稀硫酸或H 2S地层水中更易发生溶蚀作用,形成有效的孔缝洞,从而有利于油气的运移和储集.

As one of the most important reservoirs of oil and gas resources, the formation and evolution of pore-hole-fracture in oolitic carbonate reservoirs had attracted extensive attention. Based on oolitic carbonate slice, we observe the microstructure and chemical characteristics of the samples before and after the dissolution experiments in dilute sulfuric acid, through the microscope, scanning electron microscope (SEM) and energy spectrum (EDS). The results show that the dissolution of carbonates varied according to the structure and compositions of the samples. On microstructure observation, oolitic dolomites can produce much more dissolution pore to form effective reservoir than the oolitic limestones. The weight losing percentage of oolitic dolomite (1.04,) caused by dissolution in 12 hour is more than that of the oolitic limestone (0.70,). Through the EDS, we find that the variance of compositions is the key factor of dissolution. The sites with various element contents are easier to dissolute. It is shown that in oolitic dolomites there is lower Mg/Ca value (0.6 ~ 0.8) at the dissolution part than at the other parts. The higher degree of dissolution depends on the higher content of Mg element, resulting in the decreasing of Mg/Ca. We also find that there is weak dissolution at the site with high contents of Si and Al in oolitic limestone. This shows that the quartz and feldspar might prevent sample from dissoluting. It is concluded that oolitic dolomite could form a large number of interconnected pore-hole-fracture in formation water enriching dilute sulfuric acid or H2S, which is conducive to the migration and reservoir formation of oil and gas.