Research On The Characteristics Of Pre-salt Lacustrine Carbonate Reservoir In Lula Formation,Santos Basin,Brazil

The Santos pre-salt system is rich in oil and gas resources and has huge potential for exploration in Brazil.As one of the largest oil and gas fields,the study on the basic characteristics of the reservoir,the genesis mechanism of the reservoir,and the development and distribution characteristics of the reservoir is relatively weak.In this paper,by combining core observation,thin section identification,seismic data,well logging and logging data,the basic features of the pre-salt lacustrine carbonate reservoirs in the Lula Oilfield of the Santos Basin in Brazil,the reservoir genetic mechanism,and reservoir development and distribution characteristics were studied.The results show that:(1)The rock types of the pre-salt lacustrine carbonate rocks in the Lula oil field are mainly spherical microbial limestone,stratified limestone,dendritic microbial limestone,intercalated limestone,and granular limestone;(2)The type of reservoir space is mainly intergranular dissolved pores,intragranular dissolved pores,and dissolved pores,followed by biological lattice pores,fractures,intercrystalline pores and intercrystalline dissolution pores in the study area;(3)The diagenesis types in the study area are diversity,mainly including cementation,compaction,pressure resolving,recrystallization,dolomitization,silicification and dissolution.Among them,the dolomitization,silicification and dissolution are closely related to the formation of reservoirs in the study area.Relevant and further divided into three types of dolomitization,two types of silicification and three types of dissolution.Among them,three stages of dolomitization include syngeneic dolomitization,buried dolomitization and hydrothermal dolomite,two phases of silicification including early silicification and late silicification,period dissolution including atmospheric water and early diagenesis water dissolution,burial phase dissolution and hydrothermal dissolution,for different types of effects,combined with the geological background of reservoir formation,to explore and establish a corresponding role Mechanisms and patterns;(4)The reservoir formation space formation mechanism in the region is mainly the water-solubility of the early diagenesis associated with the unconformity surface during the contemporaneous period,resulting in the formation of mold pores,intragranular dissolution pores,intergranular pores during the burial period dolomitization.During the burial period,organic acidic water-solubilization formed intergranular dissolution pores,intergranular dissolution joints,and dissolution pores.During the buried period,hydrothermal corrosion formed joint pores;(5)There are four types of reservoirs developed in the study area,including tidal ash reservoirs,reef limestone reservoirs,dolomite reservoirs,silicified siliceous reservoirs,tidal limestone reservoirs and reef limestones.The tidal ash reservoirs and reef limestone reservoirsreservoir is the most developed,and the reef limestone reservoir has the best reservoirability,followed by the beach limestone reservoir.