Characteristics Of Microbialites Reservoir Of Leikoupo Formation In The Western Sichuan Basin

Based on Hanwang section,Pz115 and YaS1,using thin section ident,cathodoluminescence image,SEM,⁸⁷Sr/⁸⁶Sr and trace element analysis to analyze the sedimentary structure types,sedimentary microfacies types and distribution of microbialites,microbes and their developmental environments,pore types,physical characteristics,diagenetic types and sequences,dolomitization diagenetic fluid sources of microbialites reservoir of the Leikoupo Formation in western Sichuan.Finally,discussing characteristics of microbialites reservoir and their main controlling factors.There are three sedimentary structure types of microbialite in the Leikoupo Formation in the study area:thrombolite,stromatolite and coating structure.The microbes including Renalcis,Girvanella,Epiphyton and Gloeorrh.The microbes morphology is ellipsoidal or oblate spheroidal,incomplete spherical or hemispherical,spheroidal aggregates,flakes and isolated spheres.The developmental environment of microbes in the study area is Anoxic,hot and humid climate,high salinity of marine salt water,and the semi-opened confined bay under the enclosure of the study area-Longmenshan underwater uplift.There are seven types of microfacies of microbialites in the Leikoupo Formation of the study area:thrombolite?MF1?,stromatolite?MF2?,thrombolitic stromatolite?MF3?,microbial grid rock?MF4?,bonded aggregated granular rock?MF5?,oncolite?MF6?,spheroidal bonded rock?MF7?.From Hanwang to Longshen1 is marginal mound and beach,and the eastward was dolomitic limestone flat,microbial mound and beach and lime-dolostone flat microfacies.The microbiolites reservoir of Leikoupo Formation in the study area is affected by various diagenetic processes,including micritization,two-stage dolomitization,four-stage cementation,two-stage dissolution,compaction and pressure dissolution,recrystallization and tectonic fracture.The sea water during the sedimentary period is source of the syngenetic-penecontemporaneous dolomitization fluid,and the hydrothermal fluid is source of the buried dolomitization fluid.The pore types of the microbiolites in the Leikoupo Formation in the study area mainly include microbial framework pore,dissolution pore,intercrystalline pore and pane pore.The reservoir is generally low porosity and low permeability,and the overall physical property is shown as the stromatolite>thrombolitic stromatolite>thrombolite>non-microbiolites.The main controlling factors of the microbiolite reservoir in the Leikoupo Formation in the study area are as follows:1)the extreme paleoenvironment,paleoclimate,paleostructure and paleogeography conditions control the growth and development of microbes,making the microbiolite a favorable reservoir.2)dolomitization is the key to forming a high-quality reservoirs of microbiolites.3)buried dissolution promotes the improvement and maintenance of microbiolite reservoir.Whether or not the dissolution occurs under buried conditions is directly related to the quality of reservoir.