Reservoir Characteristics Of The Fourth Member Of Leikoupo Formation,Western Sichuan

Based on the former studies of the sequence stratigraphy,the cores and the slice analysis of the fourth member of Leikoupo Formation's carbonatite,we established the sedimentary facies classification scheme,which is suitable for the fourth member of Leikoupo Formation in Western Sichuan.We believed that,during the period of the fourth member of Leikoupo Formation,tidal flat is the mainly facies in Western Sichuan.Further more,3 subfacies(supratidal zone,intertidal and subtidal)can be identified,and the intertidal is the most developed subfaces.The sedimentary processes is as follows: during the early period of,the sedimentary environment is mainly algae dolomite flat and dolomite flat,and mainly developed grain dolomite,algal dolomite and algal lamina dolomite;during the later period of,the sedimentary environment is dolomite ash flat and algae dolomite ash flat,main developed dolomitic limestone,algal limestone and grain limestone.Due to the gently topography,the sea-level changes influenced the sedimentary environment significantly,leading the sedimentary microfacies changed frequently.By analyzing the drilling cores and thin slice of 8 key wells,we divided the 28 types of the rock of into 4 subclass,12 small classes.And furthermore,we described the characteristics of the reservoir petrology and the degree of the reservoir development.There are many types and forms of the reservoir space,the main types are intracrystalline pore,intercrystalline solution pore,irregular solution pore,fenestrule,fracture,dissolved fracture,karst cave and few interparticle dissolution pore,mold pore,and the reservoir space is maldistribution.According to the origin,the geometrical morphology and the size of the space,we divided the types of the reservoir space into 2 classes,the primary reservoir space and the secondary reservoir space.(1)Primary reservoir space is mainly composed of primary intergranular pore and fenestrule;(2)secondary reservoir space is mainly composed of secondary pore(intracrystalline pore,intercrystalline solution pore,irregular solution pore,interparticle dissolution pore,mold pore.),karst cave and fracture(structural fracture and solution fracture).Based on the reservoir physical characteristics,we think that,mentioned to the reservoir physical properties,Dolostone is better than limestone.The ? type and the ? type reservoir space is mainly developed intercrystalline pore,inter-algae solution pore,fenestrule(bird 's eye)and karst cave.By systematacially analyzing the diagenesis of the fourth member reservoir,we think that: the early dolomization,kinds of dissolution(the penecontemporaneous atmospheric water dissolution and the dissolution of the burial period)and fracturing are belong to the constructive diagenesis;the cementation excessive dolomitization and the cavity filling of authigenic mineral are belong to the destructive diagenesis,and their comprehensive influence formed the reservoir characteristics.The penecontemporaneous atmospheric water dissolution developed in the whole study area,especially in the lower dolomite reservoir,and the reservoir space is mainly composed by the acicular pore.Vertically,the thin layers of the reservoir are frequently stacked;laterally,the reservoir can be correlated at some level.The burial dissolution worked without regard to the stratum,the reservoir space is composed of the small solution pore and the extended dissolution fracture.Saddle dolomite,granular pyrite,fluorite and authigenic quartz formed in the pore,which have a close relation with the fracture.The dolomite reservoir has multiple genesis feature,particularly the reservoir,which influenced by the dolomitisation,the penecontemporaneous dissolution and the burial dissolution,often has good reservoir ability.At last,we point out the favorable zones of the reservoir based on the comprehensive analysis of the sedimentary facies characteristic,the reservoir characteristic,the diagenesis and the key controlling factor.