Thrust Structure And Its Effect On Hydrocarbon In The Western Margin Of Ordos Basin

Based on the 2D seismic data,logging and field outcrop data of the study area,the analysis of the structural features and evolution of the western thrust belt were conducted,and their effect on the formation hydrocarbon communication have been discussed to predict the favorable exploration target.This paper firstly studies the seismic stratigraphic reflection markers and geological horizons.On the basis of discriminating the seismic polarity,the seismic profile was verified based on the strong amplitude reflection mark layer of the Shanxi-Taiyuan coal seam and the Jurassic coal seam.At the same time,the weak reflection of the Middle and Lower Triassic sandstone and mud-stone and the Jixian system were identified,as well as weak reflection generated by dolomite.Secondly,in the seismic section,the unconformity of the strata that is important for the development of the study area is identified: the unconformity of the top boundary of the Proterozoic rifting sequence,the unconformity of the top boundary of the Lower Paleozoic,the unconformity of the top boundary of the Triassic and the bottom boundary of the Cretaceous.By means of equilibrium section and fission track annealing age analysis,the distribution of the Upper Paleozoic in this area was basically clarified by making pre-Cretaceous paleogeologic maps after confirming that the thrust orogeny and uplift and denudation of the Late Jurassic were the main causes of formation loss.The western margin of the Ordos Basin formed different tectonic styles under the restriction of EW compression,dextral strike-slip external force and boundary faults with different strike directions during the Yanshanian Stage.The northern part of the Zhuozishan section is characterized by fold thrust belt,the Taole section is an eastward dipping fault block,the central part of the Majiatan section is a slip-off hedge fold,and the southern part of the Tianshuibu section is a westward dump block.The Shajingzi section has a strike-slip compression-torsion oblique thrust and flower-like fault fold.The conditions of formation erosion,hydrocarbon preservation and reservoir formation vary greatly with different structural styles.The strata of the same eastward dipping fault block are less denuded,and the strata of the flower-like fault fold steep narrow zone are more denuded,and the thin-skinned structure is better preserved than the flower-like structure.Based on the structure,hydrocarbon generation,reservoir and oil and gas preservation conditions of the area,the same-direction east dip anticline in the Taole area in the northern part of the western thrust belt,the nose-like structure belt in the northeast of the Shigouyi fault and the broken nose-like zone in the west of Huan 14 well is a favorable oil and gas structural belt.