川中地区上三叠统须家河组成岩层序地层学特征

The Diagenetic Sequence Stratigraphy Characteristics of Upper Triassic Xujiahe Formation in Central Sichuan Basin

充分利用薄片分析以及X-衍射等资料,结合元素俘获(ECS)测井解释所获得的岩石矿物组合特征,从层序界面对成岩特征的控制以及不同基准面旋回内的成岩作用发育规律两个方面分别对川中须家河组层序地层格架内的成岩作用特征进行探讨。结果表明,须家河组可划分为2个超长期和5个长期基准面旋回层序。须二段、须四段底部的层序界面之下碳酸盐胶结物含量普遍增加,而界面之上的砂体普遍见溶蚀现象,储层物性相对变好。须四段基准面上升半旋回时期形成的沉积物颗粒粒度较粗、泥质含量低、砂体厚度大、连通性好,在成岩过程中原生孔隙容易得到保存,再加上受到层序界面所控制的有机酸性水溶蚀作用的影响,有利于次生孔隙的产生。而基准面下降期,砂体的连通性变差、泥质夹层增多,在成岩过程中原生孔隙不易保留同时也不利于次生溶蚀孔隙的产生,因而物性最差。须二段总体也具此规律,但由于其埋藏更深,经历成岩作用更为复杂,因此并不如须四段明显。研究成果可为研究区优质储层追踪对比及预测提供依据,同时也能为成岩层序地层学的研究提供借鉴。

On the basis of the combination features of rock and mineral using thin sections,X-ray data,Elemental Capture Spectroscopy（ECS）logging,diagenesis features of sequence stratigraphic framework of the Upper Triassic Xujiahe Formation in central Sichuan basin were studied from two aspects of controlling of sequence boundary on diagenesis and evolution rule of diagenesis within different base-level cycles.The results show the Xujiahe Formation can be divided into two super long-term sequence cycles and five long-term sequence cycles.The carbonate content in the sequence boundary for Xu-4（Member 4of Upper Triassic Xujiahe Formation）long-term sequence cycles is significantly higher,coupled with common dissolution of the sandstones above the sequence boundary,producing relatively better physical property.Sediments resulting from the long-term base-level rising cycles Xu-4are characteristic of coarse grains,low clay content,thick sand bodies,good connectivity,all of which better preserved the primary porosities during diagenesis process.While influence of organic acid water,which was controlled by sequence boundary,benefit to formation of secondary porosities.But during the falling hemicycle of base level,the connectivity of sand bodies became worse and content of clay was increasing,both of which are not favorable for primary porosity preservation and secondary porosity generation,producing worst reservoir property.This law in Xu-2（Member 2of Upper Triassic Xujiahe Formation）sandstones is overall consistent with that in the Xu-4sandstones,but it is not evident because its deeper burial depth for Xu-2sandstones and much complicated diagenesis.The research results above can not only provide guidance for the tracking contrast of high quality reservoirs in the studied area but improve the development of the diagenetic sequence stratigraphy theory.