Study On Fine Sedimentary And Reservoir Of Carboniferous Huanglong Formation In Fengjiawan Block,Eastern Sichuan Basin

The Carboniferous in eastern Sichuan has a very rich natural gas resource.In recent years,there are large oil and gas discoveries in areas adjacent to Fengjiawan area,but there has been no breakthrough in Fengjiawan area,and the unclear distribution of favorable reservoirs is the main reason restricting the exploration and development of Fengjiawan area.This paper takes the Carboniferous Huanglong Formation reservoir in Fengjiawan block in the eastern Sichuan Basin as the research object,combined with geology,well logging,core,thin slices and other data to fine divide the stratigraphy and sedimentary microfacies,and to carry out systematic research on space type,physical property and influence factors of the reservoir.Further clarified the depositional environment and distribution characteristics of Carboniferous reservoirs in this area and predict favorable reservoir facies.The traditional formation of the Huanglong Formation is mainly divided into three sections:the first section of the Huanglong Formation?C₁hl¹?,the second section of the Huanglong Formation?C₁hl²?and the third section of the Huanglong Formation?C₁hl³?.Among them,the first section of the Huanglong Formation is dominated by secondary stony limestone,the second section is dominated by micrite-powder dolomite,and the third section of Huanglong Formation is interbedded between micrite-powder dolomite and limestone.The Hezhou Formation of the Lower Carboniferous has no sediments in the area,and only the Huanglong Formation of the Upper Carboniferous remains.Generally,the distribution of the formation thickness is relatively stable,and the thickness is not very different.Because the Huanglong Formation in the study area is affected by karstification,the third section of the Huanglong Formation is completely eroded in the area,only the first and second sections of the formation are retained,and breccia is widespread.Using the existing data,combined with the regional sedimentary background,and based on the sedimentary facies mark,it is clear that the Fengjiawan block has developed a carbonate tidal flat deposition system,which is subdivided into three subfacies:supratidal flat,intertidal flat and subtidal flat.Among them,the first section of the Huanglong Formation is dominated by supratidal flat deposits,and mainly developed gypsum-tidal fades.With the continuous expansion of transgression,the second section of the Huanglong Formation is dominated by intertidal flats and subtidal flat deposits.Among them,the algae arene shoal of the intertidal flat and the shoal of the subtidal flat have good reservoir properties,and the sedimentary microfacies evolve into intertidal lagoons,shoal,intertidal algal sand flats,and subtidal static cements.But the third section of the Huanglong Formation is only survive in some wells in the study area.The intrusive process of the aquatic sediment in the area is generally from east to west.The main reservoir rocks of the target zone are?residual?granule dolomite,powder-fine-grained dolomite and dolomite karst breccia,etc.The main reservoir space types are intercrystalline?dissolved?pores and interparticle?dissolved?pores and intragranular?dissolved?pores,etc.The reservoir has the medium-low poroperm characteristics,and the reservoir type is fractured-porous.The quality is overall average and the reservoir mainly type II and III reservoirs.The heterogeneity of the reservoirs are very strong and the reservoir differences between wells are large.Favorable reservoirs are mainly controlled by high-energy lithofacies,high-energy sedimentary microfacies,dolomitization,paleo-karstification and other factors.Based on the analysis of the main controlling factors of the reservoir,the type of microfacies favorable for favorable reservoir development is bank facies deposition,which combined with the distribution law of planar sedimentary facies in the study area,characteristics of reservoir development and distribution of reservoir thickness,etc.And the distribution rule of favorable reservoir zone in the study area is predicted.