Research On The Foreland Thrust Belt And On The Accumulation Of Petroleum In The North-Western Margin Of The Jungger Basin, China

To reveal the characteristics and variation of hydrocarbon distribution, the paper discussed structural features and petroleum geology of the NW foreland thrust belt in Junggar Basin. The study involves several aspects: structural features of faults and fractures in Northwestern margin in Junggar basin, geologic models of various segments, controlling of structures on the sedimentation, tectonic setting of the proto-type basin, comparing of hydrocarbon reservoiring condition and oil and gas accumulation in every segments, etc. This paper comes into several conclusions: (1) Based on mapping prototype basins of the Northwestern Margin and adjacent area in every periods and the coupling interrelationship of basin and orogen, tectonic evolution and superposition of the proto-type basins are studied. In Northwestern Margin and adjacent area, strong arc-continent collision and orogeny occurred after the closure of the remnant ocean of Quasi-Northwestern Margin in late Carboniferous. This area experienced a foreland basin cycle during late Carboniferous to Jurassic period. Thrusting activity in the Northwestern Margin foreland thrust belt system changed in course of weak-strong-weak-inactive. Triassic-Jurassic overstep thrusting overprinted Permian piggyback thrusting. (2) Due to detailed investigation on development backgrounds and structural features of the faults and fractures in Northwestern Margin, we suggest Kelamayi-Xiazijie thrust belt is a classic leading edge of thrust characterized by thrusting, segmentation, syn-growth structures, periodical activity, etc. (3) We analyzed in detail the dynamic process of thrusting, uplifting and denudating, sediment transportation and depositing in this region. Synsedimentation faulting is responsible for the locations of various fans (alluvial fan, fan delta and subaqueous fan). In Permian, fans and thrusts propagated from the margin into interior of the basin with increasing activity and scale. During Triassic-Jurassic, propagation of thrusts and fans showed overstep style with decreasing activity and size of fan. Based on analysis of individual well sedimentary facies and seismic stratigraphy, we described development of the fans in every period and located them and revealed the superposition characteristics and diversity of Hongshanzui-Chepaizi, Kelamayi-Wuerhe, Wuerhe-Xiazijie fault belts and the fans on their frontal slope. (4) Forming and distribution of hydrocarbon reservoir in Northwestern Margin are controlled significantly by structural segmentation. We also discussed the regularity of hydrocarbon distribution in light of the coupling of the reverse faults, fans, unconformities and hydrocarbon pool formation.