PETROLEUM GEOLOGY FEATURES AND PROSPECTING TARGETS OF SIKESHU SAG, JUNGGAR BASIN

The Sikeshu Sag in southwestern Junggar basin has gone through three evolution stages since Late Triassic.Two suites of source beds,the Jurassic coal measure strata and the dark mudstone of the Anjihaihe formation of Eogene,were developed and the Jurassic coal measure is considered as the major source bed in the area.The main prospecting target strata are the sandstone and glutenite reservoir rocks of the Taxihe formation and Shawan formation of Tertiary,the Anjihaihe formation and Ziniquanzi formation of Eogene,the Tugulu formation of Lower Cretaceous,and the Toutunhe formation of Middle Jurassic.The regional cap rocks are the mudstones of the Taxihe formation of Tertiary,the Anjihaihe formation of Eogene,the Tugulu formation of Lower Cretaceous,and the Sangonghe formation of Lower Jurassic.The threshold depth for oil generation(Ro=0.6%) of the major source rocks is about 5000 meter underground and the peak of oil generation and drainage was in Himalayan,which matched the trap-forming period of the sag.In Sikeshu Sag,the eastern zone of the Ai-ka structural belt,the Tuositai structural group,and the perdu anticline belt under the nappe of Northern Tianshan Mountain are the main targets for oil-gas prospecting.