Sedimentary facies,sedimentary model and evolution of Changxing Formation in northeast Sichuan basin

Changxing Formation in northeast Sichuan basin is marine deposit which can be divided into platform margin organic reefs,platform margin shoals,open platform,limited platform,carbonate ramp,basinal facies and platform evaporite facies.Affected by second-grade sea level changes,the transgressive reef-beach bodies are well developed in Changxing Formation,forming two types of favorable reservoirs.The reef-beach facies migrated and uplifted in vertical direction and developed in zonal form on both sides of the basin,controlled by sedimentary facies.The main sedimentary microfacies comprises organisms-bearing dolomite microfacies,sparry grained dolomite microfacies,gravel dolomite microfacies,dolomite mudstone microfacies,organisms-bearing calcite microfacies,sparry grained calcite microfacies and ostrocoda limestone,of which the most favorable microfacies are gravel dolomite microfacies,organisms-bearing dolomite microfacies and sparry grained dolomite microfacies.Based on detailed research on the characteristics of sedimentary facies,drilling data,outcrops,core and thin section observation,the authors have built the sedimentary model and evolution model of the study area and compiled the sedimentary facies distribution map.