| The Santos Basin is one of the hotspots in global oil and gas exploration today in Brazil.The lacustrine microbial carbonate reservoirs developed under the salt has received widespread attention in the world.Under the premise of fully grasping the regional geological background,a combination of core disciplines,seismic stratigraphy,sedimentary petrology,and other multidisciplinary theories combined with core observations,microscopic observations,drilling,logging,and Based on a comprehensive analysis of seismic profiles,a series of sedimentary facies of the lacustrine carbonate rocks of the Lower Cretaceous Barra Velha Formation in the Lula field of the Santos Basin was developed.The Barra Velha Formation is divided into two third-order sequences(SQ1,SQ2)in the study area.These two three-level sequences are composed of the TST and the HST,and the lower system tracts are not developed.(LST).The lower three-stage sequence(SQ1)can be divided into five four-level sequence.The upper three-level sequence(SQ2)is divided into seven four-level sequence.Three-stage sequence grids on seismic profiles and four-step sequence grids on drilling profiles have been established.The three factors of lake level rise,paleotopography,and tectonic movement jointly controlled the development of the third-order sequence and high-frequency sequence of the Lower Cretaceous Barra Velha Formation in the study area.The Barra Velha Formation identified a total of 14 major rock types in three major categories in the study area.Among them,mechanical-chemical sedimentary carbonate rocks include breccia limestone,internal detrital limestone(sandstone limestone,conglomerate limestone),bioclastic limestone,granule microcrystalline limestone,and grain-containing microcrystalline ash.Rocks,microcrystalline grain limestones,microcrystalline limestones;microbial carbonates include dendritic rocks,stromatolites,karst rocks,lamellar rocks,and spherical microbial limestones;metagenic carbonates include dolomites and siliceous rocks.The Barra Velha Formation in the study area identified two sedimentary sub-facies of the lakeshore and shallow lake(carbonate platform).The sub-facies of the shallow lake(carbonate platform)identified six microfacies of internal clastic beach,shell shoal,spherical microbiological beach,microbial reef,beach(reef),and depression in Taiwan,and the lake subphase identified the shoreline.The two microfacies of the ash flat.During the deposition period of 300 sections of Barra Velha Formation,the study area was mainly from northeast to southwest,showing the sedimentary pattern of the inter-beach ? platform inner shoals ? platform inner depression ? calcitie flat;during the deposition period of Barra Velha Formation 200+ 100,the study area from the northeast to southwest,the sedimentary pattern of microbial reefs? platform inner shoals ? platform inner depression ? calcitie flat was exhibited.After understanding and analyzing the distribution of sedimentary facies and fully understanding the ancient palaeogeomorphology,the Barra Velha Formation model in the study area was summarized.The Barra Velha Formation in the study area develops various types of reservoir space,including intragranular dissolution pores,mold pores,intergranular dissolution pores,intercrystalline pores,and intergranular dissolution pores,and pore-like reservoirs such as dissolved pores.Set space,storage space for biostructures,such as bio-framework holes and pane holes,and fracture-type reservoir spaces such as structural joints and erosion joints.According to the reservoir petrological facies,the evolution of the reservoir and the genesis of the reservoir,and the main controlling factors of the reservoir development,the reservoirs of the Barra Velha Formation in the study area were divided into four types: beach facies limestone reservoirs,reef-facies limestone reservoirs,and heat Liquid origin silicified siliceous rock reservoirs and dolomite reservoirs.By summarizing the distribution characteristics of the carbonate reservoirs in the Barra Velha Formation of the Lula oil field,it is believed that the most favorable facies zone for the development of the Barra Velha Formation in the Lula field should be the upper three-level sequence(SQ2).The inner clastic beach facies belt is affected by both the sedimentary environment of the facies belt and the multi-phase dissolution.The reef limestone and internal clastic limestone develop intragranular dissolution pores,casting pores,intergranular dissolution pores,dissolution pores and The corrosion space has been transformed into a reservoir space with excellent reservoir permeability,such as lattice holes and pane holes,to form a high-quality carbonate reservoir in the Barra Velha Formation in Lula Oilfield. |
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