Keywords: 
• Ertuokeqianqi /
• Ordovician /
• weathered crust /
• conceptual seismic model

Abstract: The discovery and study of Changqing Gas Field in Ordos Basin has shown the gas exploration prospect of Paleozoic,especially the weathered crust gas reservoir of Ordovician System. Ertuokeqianqi is one of the most favorable regions for gas exploration,and it has been paid much attentions for many years. Mainly based on 2-D seismic data and coupled with drilling and well logging data,we studied and described the seismic characteristics of the morphology of the weathered crust of Ordovician,Ertuokeqanqi,Ordos Basin through geological and seismic models. Firstly,through the study of drills,well logs and :sonic synthetic seismograms,we mastered the characteristic essentials of objective formations-the different conic velocity between upper Paleozoic and lower Paleozoic and the two coal formations and their seismic cha-acteristic .At the same time,we also understood the relations of Lithology and Logging parameters, which lays a foundation for developing seismic models. Furthermore,we divided the shapes of the Ordovician weathered crust into four conceptual models,namely, paleotableland,paleopit, paleovalley and paleoslope. Using these models,we elementarily established the corresponding relations between paleogeomorphology and seismic characteristic with the analysis and comparison of geological models,seismic reflection and practical reflection. We have found that the dis- tance between the lower coal formation and Ordovician weathered crust had important relations with the seismic characteristics. Finally,this research is very valuable to interpret and calibrate the weathered crust of Ordovician system on seismic log and to draw the horizontal maps of the relic Ordovician formation over the M55. The maps might reflect the morphology of the weathered crust,and which is helpful to find Ordovician weathered crust gas reservoir and direct the gas exploration in Ertuokepianqi, Ordos Basin.