鄂尔多斯盆地东部二叠系山西组23段石英砂岩砂体结构类型及成岩作用差异

摘要

鄂尔多斯盆地东部子洲—清涧地区二叠系山西组23段石英砂岩区块单井产能与砂体结构类型具有一定相关性.基于单砂体垂向粒度韵律和自然伽马测井资料,将砂体结构划分出块状型砂体、正粒序型砂体和叠加型砂体3种类型.通过铸体薄片鉴定和粒度分析实验,对3种类型砂体储集层在成岩作用类型、特征、发育程度、产物、垂向变化及成岩孔隙演化的差异性进行表征.研究表明,3类砂体的溶蚀作用、压实作用强度及分布特征存在较大差异,粒度及其垂向分布是制约不同结构类型砂体成岩演化的直接因素,进而影响储集层物性,决定了含气层与致密层的垂向分布规律.块状型砂体储集层原生孔隙、次生溶孔共同发育,含气层厚度较大,局部致密.正粒序型砂体垂向物性差异较大,中—下部储集层溶蚀程度较弱,以原生孔隙为主,次生孔隙少量发育,为含气层;上部储集层压实、胶结作用强烈,相对致密.叠加型砂体储集层形成于河流控制作用逐渐增强的过渡环境,兼有正粒序型、块状型砂体的特征,多层含气且厚度大.%There exists a certain correlation between sandbody architectures and single well production of quartz sandstone of the Member 23 of Permian Shanxi Formation in the Zizhou-Qingjian area in the Ordos Basin.Based on the vertical grain-size cycles of the individual sandbody and natural gamma logging data,the sandbody architectures of the study area has been divided into block,normal grading and superimposed types.The paper shows the differences of diagenesis in types,characteristics,intensity,products,vertical variation and pore evolution of the three type sandbodies by casting thin sections observation and particle size analysis.The study shows the intensity and distribution characteristics of the dissolution and compaction of the three type sandbodies are quite different.The vertical distribution of particle size is the direct factor that restricts the diagenetic evolution of the different types of sandbodies,which in turn affect physical property of sandstone reservoirs and finally determine the vertical distribution of gas-bearing layer and tight layer.The reservoir of the block type sandbodies has both primary pores and induced pores of which the gas-bearing layer is thick and tight layer is locally developed.The middle and lower part of reservoirs of normal grading type sandbodies are characterized by poor dissolution degree,which have more primary and less induced pores and are gas-bearing layer.The upper part of reservoir is tight due to strong compaction and cementation.The superimposed type sandbodies formed in the sedimentary environment of gradually strengthened fluvial influence have characteristcs of the both two former types,with the gas-bearing layers are thick and multizone.