从前侏罗纪古地貌的角度论鄂尔多斯盆地靖边—鄂托克前旗地区油气成藏模式

以陕北斜坡靖边—鄂托克前旗地区下侏罗统延安组延9油藏为例,运用印模法恢复了前侏罗纪古地貌形态。研究表明:研究区古地貌主要为高地、斜坡、河谷和河间丘4种古地貌单元。在此基础上分析了富县组+延10段沉积相带展布以及前侏罗纪古地貌对延9油藏的控制作用,认为古地貌景观基本控制了富县组及延安组下部的沉积相带展布。古河谷的下切作用不仅使延9段与延长组油源层的接触距离缩短,而且为油气运移提供了良好的通道,如遇到有利的储集体与背斜和鼻隆等构造,即可有机配置和富集成藏。存在两种成藏模式,即河间丘区-分流河道组合式和斜坡区-分流河道组合式。指出前侏罗纪古地貌斜坡区与河间丘区是下一步延9段油藏勘探的有利地区。

Accumulation model of Jingbian—Etuokeqianqi area in Ordos Basin from angle of pre-Jurassic palaeogeomorphology

Taking the number 9 oil reservoir of Yan’an Formation of Low Jurassic in Jingbian—Etuokeqianqi area of Ordos Basin as an example,the palaeogeomorphic form of the pre-Jurassic was reconstructed by the mold method.The pre-Jurassic palaeogeomorphic framework is divided into upland,slope,river valley and mound.On that basis,the sedimentary facies belts distribution of the Fuxian Formation and the member 9 of the Lower Yan’an Formation and the pre-Jurassic palaeogeomorphic form control on the number 9 oil reservoirs were studied.The palaeogeomoyphic form had a certain control on the sedimentary facies belts distribution of the Fuxian Formation and the Lower Yan’an Formation of Lower Jurassic.The incision of the palaeo-valley not only decreases the distance between the Lower Yan’an Formation and the hydrocarbon source intervals,but also provides hydrocarbon migration pathways.If there exist profitable reservoirs combining with anticline and nose-up lifting structures,they can entrap hydrocarbons and form hydrocarbon reservoir.Two palaeogeomorphic reservoir models,i.e.,slope-distributary channels combination model and mound-distributary channels combination model,are generalized,and the pre-Jurassic palaeogeomorphic slope and mound are the profitable areas for the exploration the member 9 of the Lower Yan’an Formation.