四川盆地川中—川西地区沙溪庙组层序地层特征

Research on the sequence stratigraphy of the Shaximiao Formation in Chuanzhong-Chuanxi area,Sichuan Basin

河流相是中国中、新生代陆相盆地重要的油气储层类型,而河流相地层划分一直以来也是一个难点。四川盆地川中—川西地区沙溪庙组发育河流相沉积,以陆相高分辨率层序地层理论为指导,通过“点—线—面”结合,对其开展层序地层研究。结果表明:①沙溪庙组可划分为3个三级与5个四级基准面旋回;5个四级旋回分别与沙一段,沙二1、沙二2、沙二3、沙二4亚段对应。②基准面旋回是控制沙溪庙组河道发育特征和叠加样式的主控因素;基准面较高时,可容纳空间大,地层沉积速度快,河道相对孤立,规模较小,地层泥岩含量较大;基准面较低时,地层沉积速率慢,河道原地摆动时间长,相互切割叠置,河道规模较大,地层泥岩含量相对少。沙溪庙组层序地层划分不仅提供了一个高精度的等时地层格架,同时也具有储层预测作用,对沙溪庙组天然气勘探具有重要意义。

Fluvial facies is a significant type of hydrocarbon reservoirs in Mesozoic and Cenozoic continental basins in China,while the strata division of fluvial facies has always been a difficult theme.In Chuanzhong-Chuanxi area of Sichuan Basin,Shaximiao Formation developed fluvial facies.Based on the theory of continental high resolution sequence stratigraphy,combined with the principle of point-line-plane,this paper attempted to carry out sequence stratigraphy research on Shaximiao Formation.The results showed that:(1)Shaximiao Formation can be divided into three third-order base-level cycles and five fourth-order base-level cycles.The five fourth-order base-level cycles respectively corresponded to the first member,section 1 in second member,section 2 in second member,section 3 in second member,section 4 in second member of the Shaximiao Formation.(2)The base-level cycle affected the development and superimposed pattern of the source channel.When the base-level was high,the accommodation space was large,the strata got deposited quickly,and the channel was relatively spatial independent with small scale,the mudstone content was large.Differently,when the base-level was low,the strata got deposited slowly,the channel migrated frequently and incised each other,resulting in the formation of large scale channel,and the content of mudstone was relatively low.The sequence stratigraphic classification of Shaximiao Formation not only provided a high resolution isochronous stratigraphic framework,but also has a function of reservoir prediction,which is of great significance for gas exploration and development of the Shaximiao Formation.