Seismic Sedimentology Study in the High-Resolution Sequence Framework——A Case Study of Platform Margin Reef-Beach System of Changxing Formation,Upper Permian,Yuanba Area,Northeast Sichuan Basin,China

The Yuanba(元坝) area is considered another potential large-scale reef-bank gas field following the Puguang(普光) field.However,there are lots of difficulties on the spatial and temporal distribution of reef-beach and the detailed prediction of the effective reservoir in the sequence stratigraphic framework.In this paper,based on the seismic data,well,log and core,we conduct a high-resolution sequence division and build an isochronal sequence stratigraphic framework for the Changxing(长兴) Formation by the methods of wavelet transformation,FMI,etc..Then,the corresponding relationship among the lithologic facies,logging facies,seismic facies,seismic attribute facies and reservoir of Changxing Formation were established through well-seismic calibration and geological-geophysical modeling.Furthermore,detailed study on the spatial and temporal distribution of microfacies of the reef-beach was carried out by means of seismic attribute extraction.Meanwhile,combined with impedance inversion,the spatial distribution of porosity of reef-beach reservoir was predicted.The results show that the revolution of the reef-beach system contains three stages which are initial bioclastic bank establishment stage,reef development stage and exposure stage.Also,porosity inversion shows that the region with high value of porosity is located in the reef cap,fore reef and back reef.