鄂尔多斯盆地南梁西区延长组层序地层格架与生储盖组合特征

Sequence stratigraphic framework and source-reservoir-caprock assemblage of Yanchang Formation in western Nanliang area, Ordos Basin

为研究鄂尔多斯盆地南梁西区上三叠统延长组层序地层格架与生储盖组合特征,采用高分辨率层序地层学的原理和方法,对该区层序界面类型、层序地层格架特征及长期基准面旋回与生储盖组合的关系进行了研究。结果表明:研究区共识别出5个三级层序界面,将延长组划分为1个超长期和4个长期旋回层序;生储盖组合特征与长期基准面旋回的关系密切,在长期基准面上升半旋回早中期和下降半旋回晚期发育的三角洲平原分流河道及前缘水下分流河道砂体为优质储层,在长期基准面上升半旋回晚期和下降半旋回早中期发育的浊积岩砂体为潜在储层,在长期基准面旋回升降转换面附近发育的湖相泥页岩及炭质泥岩为良好的生油层和盖层;延长组发育上生下储、下生上储及自生自储式生储盖组合。

In order to study sequence stratigraphic framework and source-reservoir-caprock assemblage of Upper Triassic Yanchang Formation in western Nanliang area, this paper studied the sequence boundary types, the characteristics of sequence stratigraphic framework, and the relationship between long-term base-level cycle and source-reservoir- caprock assemblage by the theory and approach of high resolution sequence stratigraphy. The result shows that five third-order sequence boundaries are identified, the Yanchang Formation consist of four long-tern and one super-long term base-level cycles. The source-reservoir-caprock assemblage has close relation to the long-term base-level cycle. The sand bodies of delta plain distributary channel and front underwater distributary channel developed in the early- middle stage of the uprising periods and middle-late stage of subsiding periods are high quality reservoir, the turbidite sand bodies developed in the middle-late stage of the uprising periods and early-middle stage of subsiding periods are potential reservoir, and the lacustrine shale and carbon mudstone developed in the surrounding of transforming interface of uprising to subsiding of the long-term base-level cycle. The Yanchang Formation developed three types of source-reservoir-caprock assemblage, including upper-sourcing and lower-reservoiring type and lower-sourcing and upper- reservoiring type and self-sourcing and self-reservoiring type.