The Development Of Original Basin In Late Hercynian Period And Its Control For Oil-gas Forming In Bogda Region, Xinjiang

The Bogda region, located along the north margin of Tianshan Mountain, is the key region for oil-gas exploration in China. There are the strata of the upper Paleozoic and the following every time in the region, but the Lucaogou formation and Hongyanchi formation in Permian, two reservoirs and cover rock in Jurassic, two expulsives in Yanshan era and Himalaya era are well developed. Based on the analysis of mineralogical component, invariable element, traceelement and rare earth element, the Bogda volcanics's features are the same to the volcanics's of continental rift type. the same flowing direction of the palaeocurrent of the volcanic rock in Ao'ertu formation at the south and north Bogda suggests the Bogda Mt.in late Paleozoic belongs to continental rift structure environment, as they have no the visual features of wings flowing differently which is the feature of island arc. The basin mainly developes the two phrases in late Hercynian era: one is that the time of early volcano and coherent sedimentation and development; the other is that the filling time of late terrigenous rock. The filling time of terrigenous rock is from the Carboniferous and Permian transition time and the main representation is that a large quantity of far distance deposit flows into the Bogda region. The sedimentation paleogeographic feature in early Permian inherits the feature in late carboniferous basically, but the depocenter moves to north obviously. The early deposit in early Permian at the south and north side of the Bogda Mt.is the same source and has the same spread direction. At the late phrase, the deposit spreading direction of the south slope in the Bogda Mt. and Chaiwopu area shift to the direction of north north-east. The structure of basin in late Permian inherits the structure in early early Permian and the main source locates the north in the basin, but the deposit source of the late phrase in late Permian in Wulapo-Jijicaozi area locates the south in the basin—Tianshan area. From the analysis of development degree, organic abundance, mode and maturity of hydrocarbon source rock and the complex evaluation of the main hydrocarbon source rock spread which are in the Lucaogou and Hongyanchi formation at Dabancheng Ci'ao, the hydrocarbon source rock is divided into I,II,III,Ⅳ. The Chaiwopu region forms the embryo through the Yanshan movement and is reformed by the Himalaya movement. It includes Bogda fault-uplift zone, Bonan thrust-fault belt, Xigeda fault block structure, A'kesu anticline, Shangsi structure in Xigou, Baiyanghe-Xialeijiagou-Xigou structure and Dabancheng structure. According to the match between the evolution of hydrocarbon source rock and structure and connecting the complex evaluation of hydrocarbon source rock which is in Lucaogou formation and Hongyanchi formation in upper Permian, the structural traps in Chaiwopu region is concluded three exploration zone belts: the most advantageous, the advantageous and the disadvantageous, which provide the correct direction for the oil exploration.