Lithofacies Combination Models And Controlling Factors Of Fine-grained Sedimentary Rocks Of The Second Member Of Kongdian Formation In Cangdong Sag

With the deepening exploration for unconventional reservoirs such as shale oil and gas,fine-grained sedimentary rocks have gradually become the focus of sedimentological research.Fine-grained sedimentary rocks in Kong2 Member of Cangdong Depression are widely developed.They are the main source rocks in the study area and the prospects for shale oil exploration.In this paper,the fine-grained sedimentary rocks of Kong2 Member in Cangdong Sag are studied by core observation and description,thin section observation,scanning electron microscopy analysis and a series of analysis and testing.Based on mineral composition and sedimentary structure,the fine-grained sedimentary rocks of Kong2 Member in Cangdong Sag are divided into six types of lithofacies(laminated fine-grained feldspar sedimentary lithofacies,block fine-grained feldspar sedimentary facies,laminar dolomite facies,massive dolomite facies,laminar fine-grained mixed sedimentary facies and massive fine-grained mixed sedimentary facies)and four types of lithofacies assemblage(assemblage 1: laminar dolomite-mixed sedimentary facies,assemblage 2: laminar fine-grained feldspar-migmatite facies,assemblage 3: massive fine-grained feldspar-migmatite facies and assemblage 4:massive dolomatism-mixed sedimentary facies.On the basis of lithofacies assemblage,conventional logging curves,such as natural gamma ray,resistivity,acoustic wave and density,which are sensitive to fine sedimentary rocks,are selected.Combining with lithology fast identification of "green mode",logging interpretation template of lithofacies assemblage is established.Vertical evolution law of various lithofacies in 1-4 subsection of second member of well G108-8 is analyzed,and sequence stratigraphic framework of fine-grained sedimentary areas in second member of east-west and north-south are established.Spatial distribution characteristics of fine-grained sedimentary facies are analyzed,and plane development rules of different lithofacies assemblages are summarized.The study shows that the sedimentation of lithofacies and lithofacies association is mainly controlled by the dual factors of land source and climate.Fine-grained lithofacies concentrate in the inner ring zone,mainly consisting of lithofacies assemblages 1 and 2;assemblage 3 is mainly controlled by terrigenous deposits in the SQ(4)and SQ(9)sedimentary periods,and assemblage 4 is more developed in the SQ(5)and SQ(7)periods controlled by climatic factors.Taking "source-reservoir co-control" as the guiding principle of shale oil dessert prediction,on the premise of synthesizing dominant source rock facies assemblages(assemblages 1 and 2)and dominant reservoir rock facies assemblages(assemblages 3 and 4),the dessert prediction of Kong2 Member in Cangdong Sag is carried out.SQ(9),SQ(5)and SQ(4)are the dessert points of shale oil and SQ(8)is the dessert point of compact oil.