Sedimentary Facies Of The Fourth Member Of Dengying Formation Of Sinian In Northern Sichuan And Its Relationship With Reservoirs

Based on the research results of predecessors,basic geological data of the research area,detailed observation and measurement of several key field profiles of the north ern Sichuan facies as well as the reservoir characteristics of the forth section of Deng ying Formation in the research area,and the relationship between sedimentary facies and reservoir was also discussed.The forth section of the Dengying Formation in the northern Sichuan Basin is relatively well exposed,contact lines of its top and base are distinct,and the top layer is gray-white mud crystal dolomite,the micrite dolomite,the origin of algae dolomite and the karst breccia which are in parallel unconformity contact with the Cambrian Qiongzhusi group,and the lower part which is characterized by gray-yellow,gray-black medium-thin layer silty mudstone and siliceous rock is in conformity with the third section of the Dengying Formation.The formation thickness has the tendency to gradually thicken from east to west and from south to north.The forth section of the Dengying Formation in the northern Sichuan Basin is in the isolated platform environment of carbonate rock.According to abundant marks of sedimentary facies and regional sedimentary background,4 types of sub-facies including the limited platform,platform margin,slope and basins as well as 11 kinds of microfacies containing dolomite lagoon,mud dolomite lagoon,grain bank,algae bond bank,algal,acclivity,siliceous sedimentation were divided.The sedimentary characteristics are summarized in such as siliceous basins.Based on the analysis of reservoir characteristics of the forth section of Dengying Formation in the northern Sichuan Basin,the relationship between sedimentary facies and reservoir was discussed in this paper.It was considered that a set of algae dolomite,aminar algal dolomite,doloarenite,oolitic dolomite,which contains abundant a set of algae bond hole,intercrystalline solution pores,dissolution pore and structural seam,a small number of intergranular pores and inner hole,it has good reservoir perfor mance with longitudinal distribution in the upper part of the forth section of the Dengying Formation.The distribution of the sedimentary facies belt is the main controlling factor of the reservoir development,and it mainly distributed in the area of Langzhong-Ningqiang in the west of North-Szechwan,and was the main oil and gas explorati on zone,the sedimentary facies could also be observed in the eastern Kang Jia Ping-Chenggu area.In the basin environment,a set of black and gray-thin mudstone and siliceous rocks are deposited,which are characterized by dense lithology,underdeveloped internal porosity and poor reservoir performance.But it is rich in organic matter,which can be regard as a good source layer and cap layer in general.