The Research On Sedimentary Reservoir Of Leikou Slope Formation In The Middle And Eastern Part Of Sichuan Basin

Sichuan Basin is the largest oil and gas basin in southern China,with a long history of oil and gas exploration.The Triassic Leikou slope group is one of the most important oil and gas reservoirs,and the exploration potential is huge.Since the last century,with the breakthrough of the exploration of the Leikou slope group in the central Sichuan Basin,the reservoirs and the related research of the Leikou slope Formation have been regained attention.According to the datas of core observation,thin sections and other research,it is shown that the middle and eastern parts of Sichuan Basin in the Middle Triassic Leikou slope period is a barrier platform sedimentary environment.The lagoon,the lagoon edge and the inner harbor are the important sedimentary facies types in this area,among which the favorable lithofacies has the best reservoir performance in the granite.The lithofacies of the intra continental shoal dolomite are mainly controlled by paleo geomorphology,hydrodynamic conditions and sea level cycles.It is distributed in the Luzhou-Kaijiang paleo-uplift under water and its micro-geomorphology with the transitional zone of the central Sichuan depression(NE distribution).In the middle and eastern Sichuan Basin,there are various kinds of rocks with rich structure,including grain,crystalline grain and biological framework.Carbonate rocks and evaporate rock are common,with carbonate content is more than 70%,which is mainly composed of dolomite,limestone and gypsum rock,and widely distributed.According to the characteristics of core,slice and logging response,it is found that the dolomite and limestone are mostly distributed in the sub-section of Leiyi~1 and the sub-section of Leisi~3,and the gypsum rock can be seen in some areas due to the later development of karstification.The main cause of the formation of granular beach type dolomite reservoirs is the sedimentary origin,and the granular dolomite and muddy dolomite deposited on the intertidal tidal flat on dry climate are the material basis and the important factors for the development of the reservoir development.Comprehensive research on drilling cores and thin slice observation shows that the lithology of the granular beach type dolomite reservoirs is granular and grain dolomite,which is dominated by grain dolomite and has a certain amount of granule(including sand,ooid,calcirudite,bioclast).The porosity of dolomite is better than that of other rocks.The control of sedimentary facies is obvious,and mainly distributed in Nanchong-Yuechi area.In the Middle Triassic Leikou slope period,granular beach superimposed karst type dolomite reservoir can be formed in the overlapping area of the beach and the residual hill.This is another important type of reservoir in this area.The reservoir rocks are mainly composed of granular dolomite and fine powder dolomite,and the pore and fracture are important to improve the reservoir performance.In general,in the relative elevation of the platform and the inner beach,the granular beach microfacies are often formed.It is favorable for the mixed water dolomitization and early dissolution to form intergranular dissolution pores and intergrain dissolution pores,eventually there forms a good reservoir.The granular beach superimposed karst type dolomite reservoir controlled by beach facies and karst paleo landform are mainly distributed in Yilong-Yingshan area.In this study,the seismic frequency spectrum technology,waveform clustering and the root mean square amplitude are used to extract the attributes of the original seismic data.And the favorable reservoir prediction area is obtained by the analysis of comprehensive sedimentary facies.In Longgang area,the reservoir of the sub-section of Leisi~3 is relatively developed,which is composed of granular beach superimposed karst type dolomite reservoir,while the granular beach type dolomite reservoirs is developed in Nanchong-Yuechi areas.