鄂尔多斯盆地吴起地区侏罗系侵蚀古河油藏分布特征及控制因素

Distribution Characteristics and Controlling Factors Analyses on Incised Paleochannel Reservoir of Valley Filling in Jurassic of Wuqi Area,Ordos Basin

以河谷充填型侵蚀古河为背景的鄂尔多斯盆地吴起地区前侏罗纪发育下切河谷、斜坡带、河间丘和低残丘4种古地貌单元类型,其中河间丘、斜坡带和低残丘是油藏的主要分布单元。斜坡带上低残丘高点、次级河道源头和二级丘嘴3种类型的位置是油气聚集重要部位。侵蚀古河谷内底水系统发育,驱动油气越过二级和三级古水系切割所形成的一级丘嘴位置,到达三级和四级古水系切割所形成的二级丘嘴位置成藏。河谷两侧斜坡产生的压力方向与区域单斜地层产生的南西—北东方向的压力相叠置时产生的合力差异,是导致古河两岸油藏赋存层位存在差别的成因机理。蒙陕古河的北东岸主要赋存侏罗系上部延安组延9油层组和延8油层组的油藏,南西岸主要赋存侏罗系下部富县组和延10油层组的油藏。

On the background of incised paleochannel of large-scale valley filling,4types of paleogeomorphology units,including incised-valley,clinoform,mound and lower monadnock,are developed in Wuqi area of Ordos Basin. Among the 4 types,mound,clinoform and lower monadnock are the main distribution units of the reservoir.The main accumulation locations of the oil are highs of the lower monadnock on the clinoform,source of the secondary river and the two-level mound mouth.Bottom water system in the incised paleochannel is well developed,which drove the oil-gas across the one-level mound mouth generated by the cutting of the two-level and three-level paleochannels,then reached the two-level mound mouth generated by the cutting of three-level and four-level paleochannels,and accumulated.The resultant force difference formed by the superimposition of the pressure generated by both sides of the paleochannel slope and the pressure generated by the regional monocline formation,causes the differences in the occurrence position of reservoirs at both sides of the paleochannel.The main occurrence positions in northeast bank of the Mengshan paleochannel are Yan 9,Yan 8 and Yan 7 oil-bearing formations of the Upper Jurassic.And the main occurrence positions in southwest bank are Fuxian and Yan 10 oil-bearing formations of the Lower Jurassic.