前侏罗系古地貌特征及其对油藏富集的影响:以鄂尔多斯盆地QY地区延安组为例

Pre-Jurassic Paleogeomorphology and Its Influence on Oil Accumulation:Case of Yan'an Formation in QY Area,Ordos Basin

为明确古地貌对鄂尔多斯盆地侏罗系下部油藏分布的控制作用,并厘定不同古地貌单元与油气成藏之间的具体关系,以鄂尔多斯盆地西南部QY地区侏罗系延安组为例,在地层、构造及沉积相研究基础上,采用印模法对研究区侏罗系古地貌进行恢复,刻画区内古地貌单元展布特征。最后,通过分析研究区延安组油藏平面分布特征与古地貌单元之间的关系,厘定前侏罗纪古地貌对油藏富集的控制作用。结果表明,研究区发育高地、斜坡、河谷、支河谷以及河间丘5种古地貌单元,其中西南部多发育高地,东北部主要发育河谷,而中部以斜坡和支河谷为主,并残留部分被肢解的高地。古地貌对油藏富集的影响不仅表现在对沉积相的控制,而且对于油藏圈闭类型及运移通道也具有控制作用,成藏模式主要包括河谷侧翼成藏和古高地成藏两种成藏模式。研究结果可为研究区延安组石油分布规律预测提供理论依据。

In order to clarify the control effect of paleogeomorphology on the reservoir distribution in the Lower Jurassic in Ordos Basin,and to determine the specific relationship between different paleogeomorphology units and petroleum accumulation,the Yan'an Formation of the Jurassic system in the QY area of the southwestern Ordos Basin was taken as an example,based on the study of stratigraphy,structure,and sedimentary facies,the ancient landforms of the Jurassic system in the research area were restored using the impression method,and the distribution characteristics of the ancient landform units in the area were characterized.Finally,the relationship between the planar distribution characteristics of the Yan'an Formation oil reservoirs in the study area were analyzed,and the paleogeomorphological units,the controlling role of the pre Jurassic paleogeomorphology on oil reservoir enrichment was determined.The results show that five kinds of paleogeomorphological units are developed in the study area,namely highlands,slopes,river valleys,branch river valleys and inter-river hills,respectively.With respect to the distribution of different paleogeomorphological units,the southwest and northeast area are dominated by highlands,and river valleys,respectively.But,middle area is mainly dominated by slopes,branch river valleys,and some of the dismembered highlands.The influence of paleogeomorphology on petroleum enrichment can be reflected not only in the controlling of sedimentary facies,but also in the types of reservoir traps and migration pathways.The petroleum accumulation models can be divided into two types,including flank accumulation in river valley,and accumulation in paleo-highland.This research can provide a theoretical basis for predicting the petroleum distribution law of Yan'an Formation in the study area.