Sedimentary Facies、structure Characteristics Of Chang8Formation And Their Impact On Reservoir In Northwest Of Jiyuan District

Jiyuan area is located in the ordos basin two complexed tectonic units with the fault developed, and the formation is complicated as well as structure, which make it a good trap basis.To find out the characteristics of fault development and accumulation mechanism,the author embarks from the two aspects of sedimentary system and structure, on the one hand describes the sedimentary facies and its distribution characteristics; On the other hand, on the basis of seismic data, analyze the structure characteristics of the study area in detail. Using these two angles as links, the accumulation effect are discussed in detail and deduce the accumulation type of research area, finally we come up with the model of accumulation, the results show that:Located in west of ordos basin, the northwestern part of Jiyuan lies in Tianhuan depression and west margin thrust belt.Since the Yanchang formation deposition of late Triassic,the area receives the influence of the yanshan and Himalayan tectonic movement, the structure characteristics of the area is relatively complexed. In Region, the Yanchang formation experienced the lake basin formation-expansion-depression-dying.When chang8reservoir sedimentary period, the lake basin began to boom, the same time the Northwestern part of Jiyuan is in lake basin boundary,with development of delta plain subfacies, some area is covered by lake level, which is called delta front subfacies. According to sand body and the plane distribution of sedimentary facies, provenance direction in the study area mainly come from the north and northwest regions, the distributary channel of delta plain can be used as an effective reservoir space,which is the favorable facies belt.We have made a description of the structure characteristics of the studied area in detail.Firstly in term of structure.the study area are divided by Tianhuan depression as axis.The eastern part develops western-tilting nose-like structure belt.In northwest part Majiatan-Gufengzhuang area is tectonic uplift belt,with southwest part Baiyanjin belonging to the low-lying zone.The formation of faults are affected by Yanshan and Himalayan two tectonic movement in research area.The SE to NW thrust faults are developed in Majiatan-Gufengzhuang uplift belt which lies on Eastern part,and in middle part Hongjingzi depression belt,the NW-SE and NWW-SEE thrust faults and Vertical fault is well developed,but the Western part Hongliugou clinoform belt is distributed by the NWW-SEE normal faults which are featured by Graben combination.According to the cause and development characteristics.it can be divided into Vertical fault、 former thrust faults、 later normal faults and proparaclase.Combined with the characteristics of three reservoir type fault-small anticline type reservoir, fault anticline type reservoir and lithologic reservoir in survey region,we think the impact what faults have on reservoir reflect in three aspects:ontrolling the migration of reservoir from lateral and vertical direction、 lateral seal and later adjustment,and sedimentary facies is characterized by provide good reservoir to form lithologic reservoir.Finally,we come up with two kinds of accumulation model:pulled by low pressure and channeled through capillary.