Research On Sedimentary Facies And Reservoir Characteristics Of The Middle-Upper Ordovician Daqing Formation In The Xichang Basin

As one of the important reservoirs,the Daqing Formation in the Xichang Basin has certain prospects for oil and gas exploration.In this paper,the cores of Wells Xide 1,Well Xide 3,and Xitan 1 were observed by measuring the Xinjigu section and Xinjianxiang section,and the cuttings of Wells Xide1,Xide 3,and Puge 1 were collected and combined with mirrors.Identification of lower flakes,cathode luminescence,carbon-oxygen isotope,strontium isotope,rare earth element analysis,and other means to clarify the sedimentary characteristics,sedimentary facies characteristics and reservoir characteristics of the Middle-Upper Ordovician Daqing Formation in the Xichang Basin,and explore the main control of highquality reservoir development The results show that:The Daqing formation in the Xichang Basin is in integrated contact with the underlying Qiaojia formation,and in unconformity contact with the overlying Silurian Longmaxi formation or the upper Triassic Baiguowan formation.According to the mode of "lithology + electricity + earthquake + Paleontology",it is separated from the upper and lower strata.The sediments of the Daqing Formation in the study area are mainly composed of micrite dolomite,laminated micrite dolomite,dense fine-grained layered dolomite,arenaceous dolomite,gravel dolomite,siliceous dolomite,sandy dolomite,dolomitic Sandstone and muddy dolomite.See storm sedimentary structure,wave mark structure and slump structure,nodular structure,dense fine-grained layer structure and biological disturbance structure.The strata of the Daqing Formation are thick in the north and thin in the south,thick in the East and thin in the west,and there are several east-west depressions.The Daqing formation in the study area is carbonate platform deposit,which can be divided into tidal flat,open platform,platform margin,platform front slope and shelf sedimentary facies,and can be divided into ten subfacies,i.e.supratidal zone,intertidal zone,subtidal zone,inner beach,platform flat,platform margin beach,upper slope,lower slope,inner shelf and outer shelf.The Daqing formation in the study area is a complete third-order transgressive regressive cycle in the vertical direction,and the sedimentary facies belt in the horizontal direction is tidal flat platform margin open platform inner shelf from northwest to Southeast.The Daqing formation in the study area has experienced multi-stage diagenesis,mainly including mud crystallization,dolomitization,recrystallization,cementation,silicification,compaction and pressure dissolution,dissolution,hydrothermal process,structural fracture and hydrocarbon filling.The characteristics of carbon,oxygen,strontium isotopes and rare earth elements show that the dolomitization fluid of the Daqing formation in the study area comes from the brine of high salinity formation after seawater concentration.The pressure solid flow of magnesium rich fluid drives the formation of the Daqing formation to produce shallow buried dolomitization,and the dolomite is formed in the shallow middle buried environment.The reservoir rock types of Daqing formation in the study area are grain dolomite and grain dolomite.The reservoir space types can be divided into dissolution hole,intergranular hole,intergranular solution hole,intracrystalline solution hole,mold hole,intragranular solution hole and fracture.The main controlling factors of reservoir development mainly include sedimentary facies and diagenesis.Sedimentary facies controls the original deposition of reservoir.Diagenesis,especially dissolution,is the key to improve the reservoir.Structural fracture connects the dissolution holes and improves the permeability of reservoir.It is an important factor for the formation of high-quality reservoir.Based on this,the contemporaneous and shallow burial of Daqing formation(quasi)in the Xichang Basin are established The reservoir development model of the period.