Faulted Structures And Effects On Oil-gas Accumulation In The Northeastern Margin Of The Ordos Basin

The tectonic uplift slope area in Northeastern Ordos Basin is characterized by multi-period differential uplift and multi-energy mineral deposits coexisting.However,there are more disputes on the re lationships of the fault combination pattern and the transition of the adjacent slope area,as well as the oil-gas accumulation in the eastern margin and the eastern margin of the basin.The outcrop fault structure survey and the fault structure of seismogenic section in adjacent subsidence slope area were mainly used,the equilibrium profile and apatite fission track(AFT)thermochronology analysis were combined,we systematically discussed the relationship between the tectonic characteristics,the transition form and its relationship with the adjacent activity belt in the northern and eastern margin of the Ordos Basin.Meanwhile,the effects of the fault tectonics-differential uplift on the oil-gas accumulation adjustment-reconstruction in the Permian were analyzed too.In this paper such conclusions can be drawn:(1)Lishi brittle-ductile fault and the west-side of the Wubu-Fugu fault nearby are together formed the strike-slip fault zone in the eastern margin of the basin,which shows a similar asymmetric flower-like assemblage pattern.The squeeze strike-slip effect of this belt mainly occurred in the middle period of Yanshanian,and then the process of uplifting in Luliang Mountain(especially in the late Himalayan)further aggravated the difference of slope.It is shown that the strike-slip fault belt on the eastern margin of the basin is an important tectonic boundary between the Ordos basin and the Lvliang Uplift(Shanxi)since late Mesozoic.(2)The Shihalagou thrust fault in the northern margin of the basin belongs to the important part of the Daqingshan fault zoon which formed in middle Yanshanian,it caused the gentle creep deformation of the south side of Boerjianghaizi fault zone and the extrusion and thrusting deformation of the former Cretaceous strata in Gaotouyao area.Meanwhile,the Huhe fault in Cenozoic caused the tectonic inversion of the Shihalagou fault and the uplifting of the Yimeng uplift.Therefore,the Shihalagou thrust fault constitutes an important tectonic boundary of the Yanshanian mid-crushing thrust and the Himalayan extensional fault depression in the northern margin of the basin.(3)The Yushuwan strike-slip fault in the northeastern margin of the basin has largely coordinated the intersectional and transformational relationship of the east-west and north-south fault structures zone,and formed the structure of wide and slow sync which surrounded by the edge of the arc fault.The primary hydrocarbon regime of the Permian in the northeastern basin is closely related to the fault-tectonic-magmatic activity in the middle of Yanshanian,and the later adjustment of primary oil-gas accumulation and secondary hydrocarbon accumulation are controlled by the Late Cretaceous-Paleogene slow uplift and the rapid uplift of the late Paleogene.