Reservoir Characteristics Of T₂l^4-3 Of The Middle Triassic In The Middle-north Area Of Western Sichuan Basin

Carbonate reservoir is hot but difficult in oil and gas exploration.Good porosity makes it hot in exploration as well as it's strong heterogeneity makes it hard to explore.With the breakthrough of Sinopec's exploration in the western part of the Sichuan Basin,the analysis of the geologic regularity in the western Sichuan Basin is of great significance to the future exploration.In this paper,a large number of rock samples were collected by means of regional data collection,field profile measurement and typical drilling coring,and a large number of thin sections were prepared.After a large number of thin section authentication,the petrological characteristics,pore characteristics and diagenetic characteristics of the study area are preliminarily recognized.Through the macroscopic grasp of the field profile,the longitudinal lithologic sequence characteristics of the core and the lateral difference of the reservoir in the middle-north area of the western Sichuan Basin,hoping to work out the petrological characteristics,sedimentary microfacies characteristics,reservoir characteristics,reservoir diagenesis,and to explore the main factors of reservoir development through the well in the middle and sections in the northern of western Sichuan Basin,hoping to do sone help to the subsequent exploration.Based on the observation of the core and the thin sections,the main rock type of the reservoir in the middle part of western Sichuan Baisin is microbial dolomite and silty dolomite with some doloarenite.In the north part the main reservoir rock type is doloarenite and silty dolomite.The study area is limited by the surrounding ancient and underwater ancient uplift in the Leikoupo depositional stage,which is characterized by shallow water,large salinity and gentle terrain.According to the sedimentary facies characteristics and signs of the Leikoupo Formation in the western Sichuan Basin,and the analysis of regional tectonic and paleogeographic background,the sedimentary facies of the Leikoupo Formation in the study area are mainly carbonate evaporation platform and restricted platform,which is divided into 11 microfacies.The reservoirs in the middle of western Sichuan Basin are dominated by microbial dolomite,and the main pores are microbial skeleton pores.The porosity is 2~8%,followed by silty dolomite,porosity is intergranular and porosity is 2%.The reservoir in the northwestern part of Sichuan Basin is dominated by silty-fine-grained dolomite,and the pore type is intracrystalline pore,whose porosity is 2%.The diagenesis in the middle and western part of western Sichuan Basin has experienced complex diagenesis,and the constructive diagenetic is the effect of dissolution,dolomitization and fracture caused by tectonic movement.The destructive diagenesis is the effect of compaction and cavity filling.Compared with the reservoir development in the middle and western Sichuan Basin,it is found that the development of the reservoir is obviously controlled by facies.The original sediments are of great significance to the development of the reservoir in the middle of western Sichuan Basin,and the later transformation by dissolution is icing on the cake.The main factors of phase change,reservoir deterioration,dissolution and dolomitization have made the reservoir development.While compared to the middle of western Sichuan Basin,the facies of the section in the northern has changed.Reservoirs were significantly worse,the main factors of reservoir development is dissolution and dolomitization.