鄂尔多斯盆地东南部山2段物源与曲流河三角洲沉积体系

The Study on Provenance and Meandering River Delta System of Shan 2 Member in Southeastern Ordos Basin

鄂尔多斯盆地东南部山2段是该盆地重要的天然气富集层位。通过重矿物分布、岩屑组分、砂岩岩屑类型及阴极发光特征分析山2段沉积物源体系,经研究认为盆地东南部山2段沉积同时受南、北部物源供源。山2段为曲流河三角洲前缘沉积亚相,碎屑颗粒分选中等偏好、磨圆较好、颗粒之间接触紧密,沉积构造主要为板、槽状交错层理、平行层理及浪成交错层理。本区山2段沉积物以跳跃组分和悬浮组分为主,水下分流河道微相粒度概率曲线呈现三段式和四段式;河口坝微相分选较好、粒度概率曲线形态为两段式和三段式。研究区北部、南部及中部志丹、甘泉等地区砂体发育较厚,剖面上河道砂体呈不对称式相互叠置,水动力条件中等—较强。通过物源体系重建、沉积特征分析与薄片特征鉴定,建立了鄂尔多斯盆地东南部山2段双物源曲流河三角洲沉积模式。该研究明确了盆地东南部山2段物源方向,明晰了山2段沉积特征,创建了典型曲流河三角洲沉积模式,为进一步勘探开发提供了理论支持。

Shan 2 Member in southeastern Ordos Basin is an important gas bearing stratum. The provenance system is analyzed based on heavy mineral distribution, sandstone composition, rock fragments type and cathodoluminescence characteristics. The sediments of Shan 2 Member mainly comes from the north and south source areas. The sorting of the sediments is moderately to well sorted and rounded. Trough cross bedding, parallel bedding and wave ripples mainly developed in Shan 2 Member, the sedimentary facies of Shan 2 Member is a meandering river delta front based on sedimentary texture and sedimentary structures. The sediments of Shan 2 Member is dominated by saltation and fea-tured by 3 sections and 4 sections while the mouth bar is characterized by well sorted sediments and 2 sections and 3 sections grain size distribution patterns. The sandstone thickness in the south, north and central areas like Zhidan and Ganquan is large. The fluvial sandstone body is characterized by an asymmetric type and stacking pattern. The hydro-dynamic condition is moderate to strong. Based on provenance system reconstruction, sedimentary features analysis and identification of thin sections, the sedimentary model of Shan 2 Member which is double sourced meandering river delta is established, which provides a theoretical support for gas exploration and exploitation.