鄂尔多斯盆地庆西古河结构、演化及成藏规律

Structure,evolution,and hydrocarbon accumulation characteristics of an ancient river in Qingxi,Ordos Basin

鄂尔多斯盆地侏罗系油藏是典型的古地貌油藏,但目前对前侏罗纪古地貌形成过程并不清楚。前侏罗纪古河记录着古地貌的形成,研究古河的结构和充填演化对进一步认识古地貌和下一步油气勘探具有重要意义。基于三维地震资料,针对庆西古河,应用古地貌恢复和聚类分析方法,明确古河的边界特征;利用多属性融合方法,刻画古河内部结构;采用地层切片,分析古河演化过程,建立古河充填演化模式。结果表明:庆西古河河谷形态西缓东陡,南窄北宽,呈U+V型结构,向北、向东逐渐加深;内部结构包括支沟、河流阶地、主河道、弯度河谷及河间丘5个次级沉积单元。基于古河整体轮廓及内部结构的精细刻画,认为庆西古河并非单一河道,主河道从早期至晚期,横向上由西向东多期迁移,纵向上复合叠加充填。主要发育2种成藏模式:古河西翼为迁移河道与斜坡背景共同控制的多阶连片油藏,古河东翼为在河道凸岸发育的受构造控制的局部点状油藏。

The Jurassic reservoir in the Ordos Basin is a typical palaeogeomorphic reservoir,the formation process of which is not yet understood.The pre-Jurassic ancient river recorded the formation of the paleogeomorphology,and studying the structure and filling evolution of the ancient river is crucial to further understanding the palaeogeomorphology and the next step in oil and gas exploration.As such,based on three-dimensional seismic data,we analyzed the boundary features of the ancient river in Qingxi using paleogeomorphology restoration and waveform clustering,and we described the internal structure of the ancient river using multiattribute fusion.We established a filling and evolution model of the ancient river using stratigraphic slices.The results showed that the ancient bottom of the ancient river in Qingxi was complicated.The valley was gentle in the west and steep in the east,narrow in the south and wide in the north,gradually deepening to the north and east,with a U-and V-shaped structure.The internal structure consisted of five secondary sedimentary units:branch ditch,river terrace,main channel,curved valley,and inter river hills.Based on the detailed delineation of the overall outline and internal structure of the ancient river,we concluded that the ancient river channel in Qingxi was not singular.The main river channel horizontally migrated from west to east in multiple stages and vertically overlapped in multiple periods.We identified two reservoir-forming modes in the ancient river in Qingxi:the western wing was a multistage,contiguous reservoir controlled by the migration channel and slope background;the eastern flank was a local point reservoir controlled by the structure developed on the convex river bank.