川西坳陷上三叠统层序地层划分新方案

川西坳陷上三叠统的须家河组与川中、蜀南等地区的香溪群在该坳陷的北、中、南段的地层对比问题，一直颇有争论，目前有四种对比方案共存，即：岩石地层、地震地层、运动界面和建议方案。为深究这一问题，据中石油和中石化两大集团公司在各自登记区块接壤的大邑地区分别进行的地震勘探和钻探工作成果，采用层序地层的研究方法进行了钻井层序与地震波组等时对比，建立了等时地层格架，进而提出须家河组与香溪群对比的最新方案：即须五段对比香四、五、六段，须四段对比香三段，须三段对比香二段；须二段部分地层遭剥蚀直至尖灭；小塘子组与马鞍塘组侧变为海相香一段。这种划分方案对复原沉积时的岩相古地理、有利相带与储层准确预测、油气资源评价都有着重要的意义。

NEW SCHEME OF SEQUENCE STRATIGRAPHIC DIVISION FOR UPPER TRIASSIC IN WESTERN SICHUAN DEPRESSION

In the northern,central and southern parts of western Sichuan depression,stratigraphic correlation has always been controversial between the Upper Trassic Xujiahe Formation in this depression and the Xiangxi Group in the central and southern Sichuan.There are 4 correlation schemes at present,i.e.lithostratigraphy,seismic stratigraphy,kinematical boundary and the proposed scheme.In order to thoroughly solve this problem,sequence stratigraphic methods are used to perform isochronal correlation between drilling sequence and seismic wave group and to establish an isochronous stratigraphic framework based on the seismic exploration and drilling results of PetroChina and SINOPEC performed separately in Dayi area bordering on their own registered blocks.A new stratigraphic correlation scheme between the Xujiahe Formation and the Xiangxi Group is presented.The 5th member of Xujiahe Formation corresponds to the 4th,5th and 6th members of Xiangxi Group,the 4th member of Xujiahe Formation corresponds to the 3rd member of Xiangxi Group,and the 3rd member of Xujiahe Formation corresponds to the 2nd member of Xiangxi Group.The 2nd member of Xujiahe Formation is partially eroded before it pinches out.The Xiaotangzi and Ma'antang formations change laterally into the first member of Xiangxi Group.The new stratigraphic division scheme is of great significance to reconstruction of the original lithofacies palaeogeography at the time of deposition,the accurate prediction of favorable faces belts and reservoirs,and evaluation of hydrocarbon resources.