鄂尔多斯盆地林镇地区延安组延9油层组地层对比与沉积微相展布

Stratigraphic Correlation and Sedimentary Microfacies of Yan 9 Subsection of Yan′an Formation in Linzhen Area,Ordos Basin

地层对比划分是石油地质研究的重要基础,而沉积相研究则有利于揭示油气的形成和油藏赋存规律。通过利用延安组煤层和炭质泥岩标志层、古剥蚀面、区域性洪泛事件标志以及沉积相分析,对鄂尔多斯盆地林镇地区延9油层组进行精细地层对比与划分,自下而上划分为延93、延92、延91共3个小层,并分析延9油层组的分布特征。研究认为林镇地区延9油层组为河流相沉积,主要发育河道、河漫滩、心滩及边滩等微相,其中延93油层组为辫状河流沉积,部分河道形态呈现一定的准"曲流化",普遍出现漫滩沼泽微相,心滩的砂体自延10期以来最为发育;延92油层组为辫状曲流河沉积,漫滩沼泽微相和边滩微相较为发育;延91油层组为网状河流沉积,漫滩沼泽微相是最主要的沉积微相单元,研究区绝大部分地区均有厚层的含炭质泥岩以及煤层的分布,边滩的分布规模和发育厚度相对减弱。同时根据地层对比、沉积相研究以及油藏剖面分析发现研究区延9油藏的圈闭类型最主要为构造—岩性圈闭油藏,少量为构造圈闭油藏和岩性圈闭油藏。

Correlation and classification of formation is basic of petroleum geology.Sedimentary faces are beneficial to reveal the law of gas-oil formation and occurrence.By means of determination of Yan′an Formation coal beds,carbonaceous mudstone marker beds,palaeo-eroded surface,regional landform flood-event markers and sedimentary analysis,we classify the Yan 9 oil-bearing formation of Linzhen area in Ordos basin into three small layers,such as Yan 93,Yan 92 and Yan 91 from bottom to top.We also describe the distribution of Yan 9 Formation.The results show that the Linzhen area was a fluvial facies sedimentary area,mainly consisted of channel,alluvial flat,mid-channel bar and point bar sedimentary microfacies.During Yan 93 Period,the sedimentary environment was the braid river;some channels were quasi-meandering and back-swamp sedimentary environments.Sand body of mid-channel bar was most developed since Yan 10 Period.During Yan 92 Period,the sedimentary environment was the braided meandering fluvial,associated with back-swamp and point bar microfacies.During Yan 91 Period,the sedimentary environment was the braided river,and the main sedimentary microfacies unit was back-swamp.Thus,the scale and thickness of the point bar decreased in this period.Massive carbonaceous mudstone and coal was formed in most of the research area.According to stratigraphic correlation,sedimentary facies and description of oil reservoir profile,the structural-litho-trap should be considered as dominating types of Yan 9 reservoir and the structural traps and lithologic traps were secondary.