The Pre-salt Lacustrine Carbonate Sedimentary Facies And Reservoirs Evaluation Of Lower Cretaceous Barra Velha Formation In Iara Field, Santos Basin

The Pre-salt lacustrine carbonate in Brazil is one of the hot topics in oil and gas exploration of the world.But the research on sedimentary facies and reservoir are relatively weak.The thesis put the Iara field's lower Cretaceous pre-salt lacustrine carbonate as an example.Combined with the theory of sequence stratigraphy,seismic stratigraphy,sedimentary petrology and other disciplines.Using sidewall coring,microscopic thin section identification,CT scanning,seismic,drilling and logging data,to carry out pre-salt lacustrine carbonate's sequence,sedimentary facies,diagenesis and reservoir research of Barra Velha Formation in Iara.The study found that the main rock types of pre-salt lacustrine carbonate are microbial limestone,grain limestone,crystalline limestone,dolomite and silicified limestone in lower Cretaceous'Barra Velha Formation.It is found that the sedimentary facies are shallow lacustrine carbonate platform reef-beach and semi deep lake slope.The study area is divided into 2 sequences?SQ₁,SQ₂?,and the sequence stratigraphic framework is established in this thesis by logging and seismic.The main reservoir spaces are various,including biological framework hole,intergranular pore,mold hole,intercristalina pore,intercristalina dissolved pore,intergranular dissolved pore,intragranular dissolved pore and so on.According to the combination of reservoir space and lithology,the reservior can be divided into four types,such as the microbial reef limestone reservoir,the beach limestone reservoir,the dolomite reservoir and the hydrothermal silicified siliceous reservoir.The microbial reef limestone reservoir and the beach limestone reservoir are the main types of reservoir.The development of reservior is controlled by the succession of ancient high spot,dissolution,dolomitization and silicification.The dissolution include contemporaneous and early diagenetic stage meteoric water dissolution,burial dissolution and hydrothermal dissolution.The dolomitization include contemporaneous dolomitization,burial dolomitization and hydrothermal dolomitization.The silicification can be divided into early silicification and late silicification.The succession of ancient high spot is the foundamental of high-quality reservoirs,making the pre-salt reservoir into zonal distribution.The dissolution is the key point to the development of reservoir.Dolomitization and silicificition provide favorable factor for the development of reservoir.Finally,this study explored the development and characteristics of the reservoir at Barra Velha formation at study area.