The Study Of Reservoir Forming Mechanism And Reservior Geologic Distribution Mode Of Cambrian In South Area Of Sichuan Basin

Cambrian constitutes14complete three cycles，the first sequence might havebeen developed in the base of ocean trough; the second sequence developed and savedcompletely in the trough, and partly saved in the both sides of the platform, the thirdsequence of strata distribute stablily. Through the single well, field sectionsedimentary facies analysis, the westen SiChuan basin was influenced by land sources,developed diamictic tidal flat, the sands were developed in the west and north ofSichuan basin, it formed a dolomitic lagoon in the centre of basin, and also, beachwhich mainly are oolitic beachs or arene beachs developed in the east and south of thelagoon.They are four types of dolomit the work area: Microcrystalline dolomite,crystal-powder dolomite, which were result of syngenetic-period dolostoneevaporation pump dolomitization, the crystal-powder dolomite or fine crystaldolomite always lumine orange light; fine crystalline subhedral-euhedral crystaldolomite which were formed in shallow burial condition lumine dark orange light.Macrocrystalline-giant crystal saddle-shaped dolomite that were in dissolved poreswere the result of the hydrothermal process, under the cathode ray there are two kindsof characteristics: firstly, the saddle-shapped dolomite is nonluminous and luminesbright orange light. Cambrian distribution pattern of rare-earth element shows that itrelatively riched in light REE than heavy REE.Crystal-powder dolomite has a lot to do with sequence system tract, it alwaysappears in LHST; Coarse-gaint crystal dolomite and saddle-shaped dolomite inslit-core-caven, and fine-crystal dolomite that are dark in centre and bright in edgedeveloped and distribute extensively, and it has little relationship with sequence andsedimentary facies. Crystal-powder dolomite and fine crystal dolomite formed insyngenetic-period oceanic sediment+sea water high salinity dolomitization;fine-crystal euhedral dolomite that are dark in centre and bright in edge formed inburial conditions and fluid restricted in the strata circulation dolomitization;saddle-shaped dolomite in dissolved pores and cavities and tectonic fissures formed inburial conditions+tectonization+fluid that origins outside strata hydrothermaldolomitization.There are3phases denudations in the Cambrian carbonate rock: The first phasedenudation marked by intragranular dissolved pores moldic pores’ developping; Thesecond phase denudation shows irregular fracture-cavity with saddle-shaped dolomitegrowth, or authigenic quartz; The third phase denudation are relevant to generation of paste dissolving pores.Through field section observation, thin slice optical observation, drilling coreobservation and bore log analyse, the research area Cambrian contains5kinds ofreservoir types: beach facies grain dolostones dissolved pores reservoir; tidal-flatfacies dolostones dissolved pores reservoir; Paste solution pores and slots reservoir;beach facies limestone dissolved pores reservoir; lagoon facies limestone dissolvedpores reservoir.HST is advantage for developping to the beach interval, beach facies isadvantage for reservoir. According to reservoir parameters of porosity andpermeability, we evaluaterate the advantage area for reservoir layers developping ofSichuan basin of the Lower Cambrian Long Wangmiao formation、Middle Cambrian、Upper Cambrian.