鄂尔多斯盆地大牛地气田马五_(6)亚段喀斯特储层分布规律

Distribution of M_(5)^(6) karst reservoir in Daniudi Gas Field,Ordos Basin

鄂尔多斯盆地马五5亚段上部发育风化壳储层,马五6亚段天然气显示良好,发育喀斯特储层。利用岩心、铸体薄片及测井等资料,采用单因素分析、综合编图法,以喀斯特角砾岩划分方案为基础,进行沉积微相、岩溶角砾岩划分,研究岩溶角砾岩相的物性特征及喀斯特储层分布规律。结果表明:鄂尔多斯盆地大牛地气田马五6亚段主要发育裂纹—镶嵌角砾岩相、角砾支撑紊乱角砾岩相、杂基支撑紊乱角砾岩相和未改造原岩4种岩相;裂纹—镶嵌角砾岩物性最好,发育有效储层,其他类型角砾岩相物性较差,储层欠发育;马五6亚段喀斯特储层受岩性及淡水条件控制,云坪微相是储层形成的物质基础,侧向淡水淋滤是喀斯特储层形成的关键因素。该结果为马五6亚段储层预测提供地质依据。

A paleo-karst reservoir is developed in the upper part of M 55 in the Ordos Basin.Gas in the M 56 Sub-member has been shown well recently,and karst reservoirs have been found by cores observation.Based on the division scheme of karst breccia,the sedimentary microfacies and karst breccia are divided by using core,cast thin section and logging data,combined with single factor analysis and comprehensive mapping method,and the physical characteristics of different karst breccia lithofacies and the distribution pattern of karst reservoir are studied.Four lithofacies are developed in M 56 of Daniudi Gas Field,Ordos Basin,including crack-mosaic breccia facies,breccia supported disordered breccia facies,matrix supported disordered breccia facies and unmodified protolith facies.Crack-embedded breccia has the best physical properties,with high-quality reservoirs,other types of breccia facies have poor physical properties and underdeveloped reservoirs.The M 56 karst reservoir is controlled by the dual factors,which are lithology and freshwater conditions.Dolomitic flat is the basis for the M 56 reservoir formation,and lateral freshwater leaching is the key factor for the formation of karst reservoirs.The results provide geological basis for reservoir prediction of M 56.