Characteristics of Stratigraphic Sequence and Classification of Petroleum Systems in the Nothern Qaidam Basin

Based on the theory of stratigaphic sequence,this paper divides the Late Triassic and Jurassic strata into 5 sequences and 12 system tracts of sequence Ⅱ and sequence Ⅲ is the main source rock in the northern Qaidam Basin.Through tracing seismic profiles,the distribution of source rocks is delineated,that is,Lenghu Nanbaxian structural zone is the boundary of Lower Jurassic (sequence Ⅱ) and Middle Jurassic (sequence Ⅲ).The research results of seismic facies and sedimentary facies indicate that the transgressive system tract of sequence Ⅱ develops extensive shallow lake and swamp facies,with small deep lake facies in the deep center,and the transgressive system tract of sequence Ⅲ develops semi deep lake facies only in Yuka sag.Based on the esearch results of stratigraphic sequence and sedimentary facies,this paper defines the oil generating centers.In addition,according to the distribution characteristics of souce rocks,the northern Qaidam Basin is divided into J1(!) R petroleum system and J2(!) E petroleum system.J1(!) R petroleum system is a petroleum system of intermediate abundance,around which Kunteyi structure,Lenghu No.7 structure and Yikeyawuru structure are favorable traps.The distribution and the thickness of J2(!) E petroleum system are limited,and hence the traps around this petroleum system have relatively small exploation potential.