三级基准面旋回内三角洲砂体骨架模型的建立——以陕北安塞三角洲露头为例

角洲砂体是中国陆相盆地最重要的油气储集层之一,建立层序地层格架内三角洲砂体骨架露头地质模型,对于三角洲砂体分布预测有重要意义。对鄂尔多斯盆地东缘多个延长组曲流河三角洲露头剖面开展了深入的高分辨率层序地层学研究,正确识别出以长61下部下切河谷底面以及对应整合面为界面的三级基准面旋回,构建了三级基准面旋回格架内三角洲砂体骨架原型模型,建立了三级基准面旋回内三角洲平原分流河道(河流)样式响应模式图。该项研究表明,三级基准面旋回过程中,不同基准面升降速率下分流河道发生规律性的下切、充填、迁移、漫溢及河型改变,控制了层序地层格架内三角洲砂体的类型、形态、规模和连通性。这对于认识三角洲砂体的分布规律,分析三角洲砂体形成岩性地层圈闭的条件有重要帮助。深入开展多种地质背景下层序格架内三角洲砂体分布规律研究,有助于实现三角洲砂体分布“成因上可解释、时空上可预测”的层序地层学研究目标。

Establishment of the Delta Sandbody Framework Model in a 3rd Order Baselevel Cycle: taking Shanbei Ansai delta outcrop as example

Delta sandbody is one of the most important continental-basin hydrocarbon reservoir in China.The establishment of delta sandbody framework model in sequence stratigraphic framework is very important to the prediction of delta sandbody.Detailed high-resolution sequence stratigraphy study has been carried out on the Upper Triassic fluvial delta outcrops along the eastern margin of Ordos Basin.The basal surface of incised fluvial valley has been recognized as the boundary of a 3~(rd)order base level cycle.Furthermore,delta sandbody framework prototype model and the evolutionary model of delta-plain distributary channel style in a 3~(rd)order base level cycle have been established.This study demonstrate that the incision,aggradation,migration,overflow and style change of delta plain distributary channel or fluvial channel should be happen regularly in response to different base-level rise and fall rate in a 3~(rd)order base level cycle,which make difference to the type,shape,scale and connectivity of delta sandbody in sequence stratigrphic framework.The discovery of this rule is important to the prediction of delta sandbody and the stratigraphic-trap forming condition analysis.Furthermore study of sandbody distribution in sequence stratigrphic framework under different geological conditions is helpful to the realization of the study object of sequence stratigrphy-"interpretable in genesis and predictable in space-time".