准噶尔盆地四棵树凹陷石油地质特征及勘探方向

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

准噶尔盆地南缘西段四棵树凹陷自晚三叠世以来经历了3个发展演化阶段.凹陷内发育侏罗系煤系地层和古近系安集海河组暗色泥岩二套烃源岩层,其中侏罗系是主力烃源岩;新近系塔西河组、沙湾组、古近系安集海河组、紫泥泉子组、白垩系吐谷鲁群及侏罗系头屯河组砂岩、砂砾岩储集层为主要勘探目的层;新近系塔西河组、古近系安集海河组、白垩系吐谷鲁群、侏罗系三工河组泥岩为区域性盖层;主力烃源岩生烃门限深度(Ro=0.6%)约在5 000 m左右,生烃高峰和排烃高峰期在喜马拉雅期,与凹陷内圈闭的形成期相匹配.该凹陷艾卡构造带东部、托斯台构造群及北天山推覆体之下隐伏背斜构造带是油气勘探的主要方向.

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.