PREDICTION OF FAVORABLE RESERVOIR FACIES BELT IN THE CHANGXING FORMATION OF WUBAITI TECTONIC ZONE,EASTERN SICHUAN BASIN

The characteristics and genesis of the reservoirs in Changxing Formation in the Wubaiti area are studied.The Changxing Formation of Permain is the major pay zone of the gas fields in the eastern Sichuan Basin and also one of the most favorable targets for gas exploration in the adjacent areas.Based on outcrop observation,core description and thin section analysis in combination with lithological,palaeontological and logging data,the Changxing Formation is divided into four main sedimentary facies,i.e.the facies of intratrough platform(deep water basin),platform slope,platform edge and open platform.Various subfacies and microfacies could be further recognized.The reservoir properties of the Changxing Formation are generally controlled by microfacies and diagenesis.Reef flat deposits,reef framework and bindstones are favorable microfacies for reservoir space.The rock types of reservoir mainly consist of grained dolomite,reef dolomite and sparry dolomite.It is conclued that favorite reservoirs could be predicted by the integrated study of all factors,in particular the spatial distribution pattern of depositional facies,the detailed facies framework of the bioreef deposits and the thickness distribution of dolomite inferred from seismic data.