Distribution of middle Ordovician Yijianfang formation in Tazhong area,Tarim basin

The bottom of the Ordovician Lianglitage formation has a series of beach facies sandy bioclastic calcarenite limestone in TazhongⅢarea of Tarim basin,and this formation is different from the bottom algal biomicrite limestone in TazhongⅠandⅡarea.Using the method of horizon cores and detritus conodont paleontological analysis,the regional conodont zones division and comparison,the comparison of the lithologic lithofacies,the comparison of the logging features and the comparison of the exposure erosion features,we found out the real chronostratigraphic ownership of this strata,and confirmed the existence of the middle Ordovician Yijianfang formation in Tazhong area.Combining the regional seismic stratigraphic demarcation and tracking to make sure the real distribution area of the strata and the favorable hydrocarbon accumulation mode.The result of the research shows that this set of calcarenite limestone belongs to the middle Ordovician Yijianfang formation,and the real distribution of the Yijianfang formation is in the Tazhong III area and the platform edge of the TazhongⅡarea.The paleokarst reservoir of the Yijianfang formation and the micrite limestone of the Lianglitage formation have potential to become the above-generation and below-storage hydrocarbon accumulation reservoir.This research has real theoretical significance for next step oil and gas exploration.