Analysis Of Depositional System Of Xingouzui Formation In Northern Jiangling Sag

Xingouzui Formation is the main producing reservoir in Jiangling Sag.However,owing to the lack of clear understanding about its sedimentary features and facies distribution,there exists confusion about the characteristics of source rock and reservoir,and the research about the deposition of Xingouzui Formation needs to be further strengthened.During the sedimentary period of Xingouzui Formation in Jiangling Sag,the salinity of the water in the study area changed dramatically,and the freshwater lake,saltwater lake as well as Saline Lake converted to each other.Based on the comparative sedimentology,this paper starts from the research upon sedimentary characteristics of modern lakes,selects Poyang Lake,Qinghai Lake and Chaerhan Saline Lake,which have the similar characteristics with the water body in the studying area at different time and different location,separately summarizes the characteristics of sedimentary and facies distribution of these three lakes,so as to build the sedimentary models of different lakes and guide the analysis of Xingouzui Formation's sedimentary.Under the guidance of diverse theories including seismic sedimentology and sedimentary system theory,this paper makes use of the logging data,seismic data and core data,on the one hand,divides Xingouzui Formation into III Oil Formation,Mud Layer,II Oil Formation,I Oil Formation and the upper Xingouzui Formation,thus establishing the stratigraphic comparison framework.On the other hand,through analyzing the rock facies and their combination in studying area,this paper identifies 4 types of sedimentary facies including fluvial facies,delta facies,lacustrine facies and saline lake facies;meanwhile,9 kinds of subfacies such as deltaic plain,deltaic front and shore-shallow lacustrine as well as 16 types of micro-facies including delta plain distributary channel,branch channel depression,delta front subaqueous distributary channel,estuary dam and shore shallow lacustrine dam are identified by analyzing the characteristic of different subfacies and micro-facies;thus clearing the traits and combination relationships of different facies,subfacies and microfacies.Combining with the logging characteristics analysis,this paper summarizes the 16 kinds of logging facies in the study area and conducts the sedimentary analysis as well as sedimentary facies comparison within the determined stratigraphic comparison framework.In addition,this paper conducts research about the lithofacies distribution features including thickness of dark mudstone,content of dark mudstone and sand ratio,well sedimentary facies and the characteristics of seismic reflection and seismic attributes of different sedimentary facies and compares the sedimentary characteristics and sedimentary models of the Poyang-Ganjiang shallow delta,Qinghai saltwater lake and Chaerhan saline lake,determining the sedimentary distribution and sedimentary model of Xingouzui Formation.It is concluded that Xingouzui Formation mainly develops delta deposits in Caifengdian,Jiangling and Shashi area,with freshwater lake sedimentary in partial area.The delta plain is broad while the delta front is relatively narrower.Influenced by lake wind and wave,beach dam sand body formed on the side edge the delta.At the same time,lake depositional system including freshwater lakes and saline lake sedimentary system developed in the southern part of studying area.