| The major reservoir of Z74 fault blockinthe second sets of oilgroup of Lower section of Es3,which is low porosity and ultra-low permeability reservoirs.This paper studies the cause of low porosity and ultra-low permeability by sedimentary facies and diagenesis.The spatial distribution of favorable reservoir were classified and studied.On the basis of cycle and hiatus,the reservoir is divided into 5 sand groups and 18 layer.The whole structure is nose shape,and the boundaries are on the East and north sides of the fault,the internal fault is thick,the structure is complex.Sedimentary environmentisoffshore deep lake sandy fan—sublacustrine fan,the source orientated from the south,which can be divided into three subfacies and nine microfacies.Cementation is the main type of diagenesis in this area.The physical properties of the reservoir is greatly influenced by authigenic clay mineral and carbonate cements.The major lithology of the reservoir is fine sandstone,secondly is the siltstone and pebbled sandstone,which the debris content is high.Core analysis shows that the reservoir's average porosity is 15.1%,average permeability is 6.5×10-3?m2,and average content of carbonate is 11.1%,which is the low porosity and ultra-low permeability structurallithologicalreservoir.Secondary pore is the main reservoir space,the primary pores include primary intergranular pore,intergranular pore and so on.Thesecondary pores include dissolved pore,moldic pore,composite large hole,micro cracks and so on.The penetration rate has a good correlation with the radius of the main stream.Reservoir inlayer heterogeneity and interlayer heterogeneities are strong.According to reservoir porosity,permeability,effective thickness and other parameters,the reservoir can be divided into three types.Based on the research of the vertical and horizontal distribution characteristics of the reservoir,the favorable zone is evaluated and predicted,andprovided a basis for the oilfield development. |
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