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鄂尔多斯盆地中东部奥陶系马家沟组(Om)发育典型膏盐岩-碳酸盐岩共生体系,其一、三、五段主要发育蒸发岩,二、四、六段多为碳酸盐岩,表生溶蚀作用影响了盐上马家沟组五段(Om_5)1~4亚段风化壳储层的形成与分布,成为靖边大气田主力产层。区内对于膏盐岩-碳酸盐岩共生体系储层岩溶效果定量评价较少,溶蚀模拟试验也多为温度、岩石成份、岩石结构、流体性质等单因素对白云岩溶蚀机理的定性模拟。因此,以基于地质条件下的溶蚀模拟试验为基础,定量评价岩溶作用对膏盐岩-碳酸盐岩储层孔隙结构的影响,指出在常压、饱和CO_2水(3%~15%)、气温30℃的封闭体系下膏盐岩-碳酸盐岩共生组合溶蚀量与膏盐含量呈正相关关系,含盐白云岩、含白云质膏岩、白云质膏岩、膏质白云岩、含膏白云岩溶蚀率依次降低,溶蚀前后孔隙度至少增加6%。含盐白云岩溶蚀率最高,达19.8%,含膏白云岩溶蚀率最低,仅为6.3%。据此提出含盐白云岩、含白云质膏岩等膏盐岩-碳酸盐岩共生体系是Om有利储集岩,经岩溶作用后孔隙度最高可提高6%~20%,从而较好地解释了Om_5含膏云坪相带存在规模优质储层的原因,并为阐明膏盐岩-碳酸盐岩共生体系岩溶储层形成机理及分布预测提供了试验依据。
The Ordovician Majiagou Formation (Om) in the middle and eastern Ordos Basin developed typical gypsum-saltstone-carbonate symbiosis system. The first, third and fifth stages mainly develop evaporites. The second, fourth and sixth stages are mostly carbonate Formation and distribution of weathering crust and reservoir surface lithology affected the formation and distribution of weathered crust reservoirs in the Member 1 to 4 of the fifth member of the Upper Member of the Majiagou Formation, and became the main pay zone of the Jingbian Gas Field. The karstification effects of gypsum - carbonate symbiosis reservoirs are less evaluated quantitatively in the area, and the dissolution simulation tests are mostly qualitatively simulating the dissolution mechanism of dolomites by single factor such as temperature, rock composition, rock structure and fluid properties. Therefore, on the basis of the erosion simulation test based on geological conditions, the quantitative evaluation of the influence of karstification on the pore structure of gypsum-salt rock carbonate reservoirs has been carried out. It is pointed out that under atmospheric pressure, saturated CO 2 water (3% -15%), Under the closed system of temperature 30 ℃, the dissolution amount of gypsum-carbonate symbiosis is positively correlated with the content of gypsum salt, salt-bearing dolomite, dolomitic gypsum, dolomitic gypsum, dolomitic dolomite, The dissolution rate of dolomite decreases in turn and the porosity increases by at least 6% before and after dissolution. The dissolution rate of salt dolomite is the highest (19.8%), and the dissolution rate of dolomite containing paste is the lowest (6.3%). It is proposed that the salt-bearing dolomite and dolomitic gypsum-bearing gypsum-carbonate symbiosis system are Om favorable reservoir rocks. After karstification, the porosity can be increased by 6% -20% This paper explains the reasons for the presence of high-quality reservoirs in the Om_5-bearing galactophore belt and provides experimental evidence for elucidating the formation mechanism and distribution of karst reservoirs in the gypsum-carbonate symbiotic system.