Study On The Controlling Factors Of High Quality Ordovician Reservoir In Yubei Area Of Tarim Basin

The largest inland superimposed petroliferous basin in China is the Tarim Basin in the northwest of China.In this basin,the development area of Ordovician carbonate reservoir is large,among which the karst reservoir has the characteristics of deep buried transformation,obvious heterogeneity,many hydrocarbon sources,the continuity and abruptness of superimposed reservoir and accumulation.The carbonate reservoir shows a very ideal exploration prospect,And gradually evolved into an important target of oil and gas resources exploration.In this study,the basic characteristics of Ordovician carbonate reservoirs in Yubei area of Tarim Basin were observed by means of casting thin section,fluorescence,cathodoluminescence and SEM.The main observation intervals are Lianglitage Formation,Yingshan formation and penglaiba formation.The main achievements are as follows:(1)According to the core data,thin section photos,fluorescence,cathodoluminescence and other technologies,five wells in Yubei area were observed,and the main components of Ordovician carbonate rocks were determined to be pure and thick limestone and dolomite,including micrite limestone and biological limestone;dolomite mainly included limestone and siliceous dolomite.According to the logging and logging data,especially the image logging(FMI),it is found that the karst of Yingshan formation of Ordovician is in the fracture development part of the fault zone,with strong karst development and large depth involved;the shale content of Lianglitage Formation is high,with poor structural fracture development;the buried dissolution holes of penglaiba formation are developed.(2)This paper summarizes the diagenesis types of Ordovician carbonate rocks in Yubei area of Tarim Basin and the main controlling factors of palaeokarst development.It is found that the diagenesis of Ordovician carbonate rocks in this study area mainly includes compaction and pressure dissolution,cementation,dissolution,dolomitization and silicification.These diagenesis are superimposed on each other and jointly control the karst development in this area.There are three main controlling factors for the development of paleokarst: paleoclimate,lithology and paleostructure.The paleoclimate provides the water supply power and thermal conditions for the development of karst.The dissolubility of carbonate is the material basis for the development of karst,and the paleostructure is the promoting factor for the development of paleokarst.(3)Based on the analysis of the karstification of Lianglitage Formation,Yingshan formation and penglaiba formation,combined with the sedimentary facies of carbonate rocks,the exposed range of carbonate rocks,the characteristics of karst palaeogeomorphology,and the development of structural fractures,the favorable areas of karst reservoirs are predicted.Most of the favorable reservoirs of Yingshan formation are distributed in the eastern fault area,which is a very typical catchment area with relatively strong water activity.Moreover,Yingshan formation is exposed on the Early Hercynian fault zone and obviously denuded.The high-quality karst reservoir of Lianglitage Formation is distributed in the lower karst slope area in the west,where the water confluence is very obvious and is not covered by mudstone.For the high-quality karst reservoir of penglaiba formation,most of them are located in the late Hercynian fault zone,and the northern low-lying zone is the most ideal one.