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鄂尔多斯盆地构造稳定,湖盆沉降速度缓慢,古地形平坦,气候干旱,湖泊面积相对较小,物源供给充足,在下寺湾油区形成了富有特色的浅水三角洲沉积。下寺湾油区浅水三角洲在骨架砂体类型、规模、形态等多方面与正常三角洲存在较大差别:平原相河道通过充填和频繁分叉汇合,向湖泊中心方向长距离推进;前缘广泛发育河道砂体,砂体呈带状分布,多个砂体垂向相互叠置,砂体厚度大,分布稳定;受可容纳空间限制和河道冲蚀作用,河口坝不发育;砂岩储层受河流控制作用明显,分叉与汇合现象普遍,砂体具有明显的方向性,砂体等厚图上呈朵状分布,砂体连通性较正常三角洲好。综合地形、气候、水动力条件等方面分析,确定了下寺湾油区各类砂体的成因及特征,并总结了下寺湾油区浅水三角洲沉积模式。
Ordos Basin is characterized by its stable structure, slow sedimentation rate, flat paleo-terrain, arid climate, relatively small lake area and adequate supply of natural resources, forming a distinctive shallow-water delta deposit in the Lower Siwan Oil Region. The shallow-water delta of Xia-Si-Wan oil-field has big difference from the normal delta in the type, scale and morphology of the skeleton sand body. The plain-phase river channel advances to the center of the lake through filling and frequent bifurcation and merging. The sand bodies of the river courses are distributed in zonal form. A number of sand bodies are vertically overlapped with each other. The sand bodies are large in thickness and stable in distribution. The sand bodies are not well developed due to confined space and river erosion. Sandstone reservoirs are affected by rivers The control effect is obvious, the phenomenon of bifurcation and confluence is common, the sand body has obvious directionality, and the sand body has a dull distribution on the isopach map, the connectivity of the sand body is better than that of normal delta. Based on the analysis of topography, climate and hydrodynamic conditions, the causes and characteristics of all kinds of sand bodies in Xiashawan oilfield are determined, and the sedimentary models of Shallow-water delta in Xiajianwan oilfield are summarized.