鄂尔多斯盆地乌审旗-靖边古隆起对奥陶系盐下沉积与储层的控制作用

Wushen-Jingbian Paleo-uplift and its control on the Ordovician subsalt deposition and reservoirs in Ordos Basin

基于钻井及地震地层对比剖面、系统性的寒武系厚度、寒武系各层段超覆尖灭线以及前奥陶纪古地质图等编图研究,发现鄂尔多斯盆地早古生代除了发育伊盟隆起、吕梁隆起和中央古隆起外,还发育乌审旗-靖边古隆起。乌审旗-靖边古隆起核部缺失整个寒武系,周缘寒武系由老到新依次向古隆起超覆。进一步的古构造分析表明,奥陶纪沉积期受寒武系乌审旗-靖边古隆起的继承性影响,该区仍为低幅度的水下隆起,对盆地中东部奥陶系盐下沉积与储层发育具有明显的控制作用。主要表现在3个方面:一是乌审旗-靖边古隆起东、西沉积分异明显;二是乌审旗-靖边古隆起、中央古隆起和吕梁隆起的共同障壁作用形成了盆地东部米脂盐洼;三是乌审旗-靖边古隆起上发育浅水沉积特征的丘滩体等有利储集相带,海退期则由于间歇性暴露而利于溶孔型储层的形成,是奥陶系盐下天然气勘探的有利区带。

A detailed study on stratigraphic correlation based on drilling data and of seismic sections,the Cambrian system thickness measurements,observation of superjacent pinch-out boundaries of intervals in the system and the pre-Ordovician paleo-geologic mapping of the Ordos Basin shows that,apart from the Yimeng and Lyuliang Uplifts as well as the Central Paleo-uplift,another uplift,the Wushen-Jingbian Paleo-uplift was also developed in the basin during the Early Paleozoic.Though completely absent from the core of the paleo-uplift,the Cambrian intervals are successively(from old to young)overlapping the uplift.Further paleo-structural analysis indicates that inherited from its Cambrian predecessor,Wushen-Jingbian was still a low-amplitude underwater uplift during the Ordovician sedimentary period and controlled the subsalt deposition and reservoir development in the central and eastern Ordos Basin.As a result,the uplift is of distinctively differentiated sedimentary facies in the east-west direction,and has played an indispensable role in joining the Central Paleo-uplift and Lyuliang Uplift to form the Mizhi Salt Depression in the east of the basin.Furthermore,with well-developed mound-shoal complexes that are typical of shallow-water deposition and prone to generate dissolved pore structures due to intermittent exposure during sea regression,the uplift is considered to be highly promising in terms of the Ordovician subsalt gas exploration.