The Characteristics Of Dolomite Reservoir Of The Fourth Member Of Sinian Dengying Formation In Moxi Area,Sichuan Basin

The paper takes the fourth member of Sinian Dengying Formation?Z₂dn⁴?in Moxi area of Central Sichuan as the research object.Through the identification of core and thin slices,and the physical and chemical analysis,drilling,logging,imaging logging data and single well of unimpeded traffic data,the characteristics of formation and sedimentary facies,reservoir petrology characteristics,reservoir space types,physical property of reservoir,diagenesis,karst zone characteristics and controlling factors of reservoir development are determined.The thickness of Z₂dn⁴ is generally distributed in the range of 261m³67m with an average of about 300m,and the strata have the general characteristics of slightly thinning from west to east.The depositional setting of the study area is carbonate limited platform,containing algae mound subfacies,grain shoal subfacies,and platform inner flat subfacies.The reservoir rocks in the study area are mainly algal dolomite and sandstone dolomite.The reservoir spaces are dominated by inter-granular dissolved pores,inter-crystalline dissolved pores and karst pores,and accompanied by multiple stages and types of cracks.The reservoir is of relatively low porosity and permeability,because of the average porosity is 3.54%,and permeability is mainly distributed between 0.01mD¹0mD,and with highly heterogeneity as well.The diagenesis of Z₂dn⁴ is very complicated,and the main diagenesis includes compaction,cementation,silicification,infilling,dissolution,recrystallization,dolomitization,and so on.Among them,dissolution is the type of diagenesis that has the greatest effect on reservoir properties.The karst of Z₂dn⁴ is dominated by vertical seepage zone and horizontal subsurface flow zone,and the horizontal subsurface flow zone can be subdivided into four horizontal subsurface flow substreams in Z₂dn⁴.The high-quality reservoir in Z₂dn⁴ is mainly affected by the sedimentary facies and karstification.The sedimentary facies provide the lithologic basis for the formation of reservoir space.The favorable reservoir facies are mainly the sub-facies of the algae that are conducive to the reproduction of microorganisms and the sub-facies of the particles with strong hydrodynamics.The diagenesis determines reservoir performance and is a key factor in reservoir formation.The strong karstification formed a large number of dissolved pores in the stratum of the study area,and these pores increase the porosity of the reservoir significantly.Therefore,the area where the strong karstification overlaps with algae mound and grain shoal subfacies is the most favorable reservoir.