鄂尔多斯盆地合水地区长8_(1)亚油层组沉积相及对储层物性的影响

Sedimentary facies of sub oil-bearing formation of Chang 8_(1) and their influence on physical properties of reservoir,Heshui,Ordos Basin,NW China

为研究鄂尔多斯盆地上三叠统延长组长81亚油层组沉积微相与储层物性的关系,通过岩心相、测井相及物性等资料,结合前人研究成果,对盆内合水地区长8_(1)亚油层组进行分析。认为:(1)长8_(1)亚油层组浅水三角洲前缘沉积发育水下分流河道、河口坝、前缘席状砂、分流间湾4种沉积微相。多期叠置的水下分流河道是控制砂体发育的主要微相类型,根据砂地比又可分为河道核部、河道中部及河道侧翼;(2)长8_(1)^(2)小层水下分流河道砂体发育频率较高、沉积期次较多、连通性较强,其次为长88_(1)^(2)小层与长8_(1)^(3)小层;(3)由沉积微相决定的岩石结构成熟度控制了储层的初始孔隙度,进而在一定程度上影响了储层现今孔隙度。水下分流河道核部储层物性最好,是有利微相类型。研究区长8_(1)^(2)小层有利微相发育规模最大,为后期勘探开发首要目的层位。

Basing on the data of drilling cores,logging records and testing of physical properties of reservoir,this paper discusses the relationship between sedimentary microfacies and reservoir physical properties of the sub oil-formation of Chang 81 of the Upper Triassic Yanchang Formation in Ordos Basin.Four types of microfacies,including underwater distributary channel,mouth bar,frontal sheet sand and inter-distributary bay,occur in the sub oil-formationof Chang 81,which is with sedimentary facies of shallow delta front.The multi-stage superimposed underwater distributary channel is the main type of microfacies controlling the development of sand bodies.According to its thickness ratios of sandstone and mudstone,it can be divided into the core,the middle and the flank of the channel.The subaqueous distributary channels occur frequently in small layers of Chang 812,whose sedimentary periods are more often than Chang 811 and Chang 813,and its connectivity is better.The structural maturity,which is determined by sedimentary microfacies,controls the initial porosity of the reservoir and then affects the current porosity of the reservoir to a certain extent.The reservoir in the core of underwater distributary channel is with the best physical properties,and it is the favorable microfacies type.It is suggested that the small layers of Chang 812,is the potential target layers for future exploration in studied areas.