The Dolomite Reservior Studies Of The Loushanguang Group In The Upper Third Series And Furong Series Of The Cambrian System In The Southeast Of Sichuan Basin

Dolomite is widely developed in the deep ancient strata，Many basins havedeveloped thick layer of dolomite. For example: The Tarim basin and the Sichuan basinat home. They have developed nearly1000meters dolomite in the Ordovician orCambria. Dolomite is one of the most important oil and gas reservoir.According toincomplete statistics, the oil and gas reserves in dolomite accounted for more than theglobal carbonate rock oil and gas reserves50%.The North American dolomite reservoirof oil and gas reserves accounted for carbonate rock oil and gas reserves80%. But thedolomite reservoir forming mechanism and the origin of dolomite, over the years, therehas been controversy. This paper through carrying out the outcrop section measuring ofthe Loushanguan group of the Cambria in the Southeast of the Sichuan basin, collectingrock samples, indoor rock sample handling, using microscopic observation, testingcarbon and oxygen isotopes, trace elements and cathodoluminescence, we system-atically study the sequence characteristics, reservoir characteristics and diageneticcharacteristics, the area of different types of dolomite formation model, analyze thedolomite diagenetic stage and diagenetic environment, and finally discusses thecontrolling factors dolomite reservoir. The main contents are as follows:(1) The rock types are mainly micritic dolostone, residual grain dolomite, crystallinedolomite and with a small amount of micritic limestone containing dolomite andgrain limestone containing dolomite，Reservoir pore type is mainly intergranularpore, intergranular dissolved pore and nonselective cavities dissolved fracture,Theaverage porosity of rock samples is6.19%, average permeability is1.822X10-3μm-2, a good correlation between porosity and permeability, reached0.85，thereservoir type is mainly porous type reservoir.(2) The diagenesis types mainly include micritization, cementation, recrystallization,erosion, compaction, pressure solution and dolomitization etc.according to theevolution of dolomite and pore, the diagenetic stage is divided into4stages and7periods, that is syndiagenetic stage. early diagenesis stage (including the early diagenetic stage of early period, early diagenesis stage of late period),the latediagenesis stage(including the late diagenetic stage of early period, late diagenesisstage of middle period, the late diagenetic stage of late period), the exodiagenesisstage. Syngenetic stage mainly include penecontemporaneous dolomitization,cementation and meteoric seawater selective corrosion, the late diagenesis stagemainly include burial dolomitization and burial of non selective corrosion, andaccompanied by hydrothermal dolomitization, Supergene stage mainly include nonselective corrosion caused by meteoric water and fresh water calcite cementation,and silicification.At the same time according to the diagenetic fluid properties, thediagenesis environment into4areas, that is penecontemporaneous near surfacediagenesis environment, shallow burial diagenetic environment, deep burialdiagenetic environment, epidiagenetic environment.(3) Different types have different genesis of dolostone. The muddy microcrystallinedolomite crystals small, carbon isotope average-1.789‰, oxygen isotope average-6.709‰, similar to the same period of seawater properties. Sr content is high, theaverage value is147ppm, cathode luminescence is a bright red, its genetic modelis evaporative pumping and recirculation osmosis; In residual grain dolostone andcrystalline dolostone, carbon and oxygen isotope mean values were-1.213%and-7.539%, Sr and Mn were low, cathode luminescence is dark red, showing its closeddiagenetic environment of marine fluid properties, its genetic model is burialdolomitization; In mottled dolomite,carbon and oxygen isotope average-1.758%and-11.234‰, Sr content is lower, cathode luminescence is dark, crystal is big,with wavy extinction, its genetic mode is hydrothermal dolomitization.(4) Dolomite reservoir is affected by many factors.High energy environment in thedevelopment of beach facies determines the range of reservoir development;Dolomitization superimposed meteoric water leaching can greatly improve thereservoir;Top good reservoir develop in shallowing upward cycles;The fracturesystem formed by tectonism can provide channels for hydrothermal corrosion fluidand can improve the dolomite reservoir effective.