Evolution And Reformation And Oil-gas Response In Ordos Jurassic Basin

Ordos Basin is one of those where oilfield is discovered at the earliest time,famous for its simple internal construction,gentle structures,stable depositional history and conformable stratum.There are rich oil and gas resources in the strata of lower Paleozoic and Mesozoic.The Jurassic era was an important period for tectonic development of the east Asia continent, and can be divided into two different deformation stages around the Ordos basin. Corresponding to evolution-reformation different stage of Ordos basin,controlling the response about source beds reservoirs seal-cap migration and pooling of oil-gas.It was under weak extension during the early to middle Jurassic, with the stretching direction in N-S to NNE-SSW, and the stretching deformation mainly occurred in zones surrounding the Ordos basin. Under stable tectonical environment during the early to middle Jurassic,sediment good reseryoirs and seal-cap for Ordos Basin.This extension was possibly associated with intra-continental stress adjustment following the late Triassic collision between the North and South China Blocks along the Qinling ranges. During the mid to late Jurassic, the Ordos basin was subjected to multi-directed compressions, with the maximum stress axe oriented in W-E, NW-SE and NE-SW; the boundary compressional belts with different trends and structural styles were formed around the Ordos basin and the basin was reshaped. The formation of the N-S trending thrust and nappe belt developed along the western margin of the Ordos basin, resulted from eastward extrusion of the Alashan and Longxi blocks; and the eastern boundary belt is characterized by W-dipping reverse faults (back-thrust) and associated folds, which is inferred to occur on the frontal hangning wall ramp of a westward propagated decollement system beneath the Shanxi Highlands. Large-scale thrust and nappe structures and inversion tectonics of the early to middle Jurassic grabens along the Daqingshan in north of the Ordos basin indicate strong N-S shortening deformation and rejuvenation of the Yinshan range. The boundary structural belts around the Ordos basin well record multi-directed compressions and continental crust thickenning during the middle to late Jurassic, which was dynamically associated with far-field effects produced by convergences toward the east Asia continent of different plates (Siberia, Paleo-Pacific, Tethys). This synchronous multi-directed compressional deformation accelerated hydrocarbon generation and should have profound impact on accumulation and localization of the multi-energy mineral deposits in the Ordos basin.