Study On Forming Mechanism And Distribution Pattern Of The Reservoirs In Longwangmiao Formation In Eastern Sichuan Basin

Lower Cambrian Longwangmiao Formation has become important reservoir rocks for oil and gas exploration within Sichuan Basin.Based on the investigation of the outcrops and the boreholes,the characteristics and major controlling factors of the Longwangmiao carbonate reservoirs in the eastern Sichuan Basin are studied with optical,EPMA observations,X-ray diffraction,carbon and oxygen isotopes analyses,as well as physical property analyses.The following conclusions can be drawn.The main sedimentary facies of the Longwangmiao Formation in eastern Sichuan Basin is a platform,on which tidal flats,grain shoals and lagoons are developed.There are many tidal flat-grain shoal assemblages.The grain shoals with high degree of dolomitization is a prerequisite to reservoir rocks.The lithology of reservoir rocks mainly consists of grain dolostones,fine-crystalline dolostones and mircocrystalline dolostones,and some partly dolomitized grain limestones.The reservoir spaces are dominated by intergranular dissolution pores,intercrystalline dissolution pores,and fissures.It is revealed that the grain shoals are the prerequisite of developing the Longwangmiao formation reservoirs,penecontemporaneous and early stage dolomitization and dissolution improve the physical properties of reservoir and the key factors to form the reservoirs.