Features And Model Of Mixed Siliciclastic-carbonate Sediments Of Da'anzhai Member In Lower Jurassic Ziliujing Formation,Huilong Area,Sichuan Basin

In recent years,we have made great achievements in hydrocarbon accumulation and enrichment regulation of the Jurassic formation of Sichuan basin.But exploration degree of different area of Sichuan basin is uneven.The study of Jurassic formation of Huilong area in Sichuan basin is of great significance to make clear oil and gas distribution of western Sichuan exploration area and to summarize its enrichment regularity.The target stratum is Da'anzhai member in lower Jurassic Ziliujing formation,Huilong area,Sichuan Basin.The purpose of this research is to establish sequence stratigraphic framework of the study area by combing sequence stratigraphic with sedimentology and classifying the types of sequence stratigraphy.At the same time,this research also build sedimentary model by using data of core,outcrop and log section to classify the types of microfacies.All of these works provide a good theoretical basis for the next exploration.The main study contents are as follows:(1)In the early Jurassic,the Sichuan basin entered into a period of continental lake basin.At this stage,a set of lacustrine-fluvial sediments have been deposited in Sichuan basin.And the study area,Da'anzhai member of Ziliujing formation of Huilong area,developed continental lake deposition.(2)With the guidance of continental lake sequence stratigraphy,making full advantage of sequence boundary outcrop marks and well logging symbols,analyzing core,log and geophysics data,based on the previous sequence classification,this paper finally classify the sequence of Da'anzhai member into one third-order sequence and 4 fourth-order sequence(SSC1~SSC4).Besides,after depicting the characteristics of cyclic sequence,a sequence stratigraphic framework is established,which lays the solid foundation for further analysis of sedimentary facies.(3)The Da'anzhai member develops the mixed sediment of lacustrine carbonate and clastic rock in Zi Liujing formation,Huilong area of western Sichuan.Combining with the outcrop observing,core describing and lots of data analyzing of logging and microfabric,it has finely depicted the characteristics of Hunji rock sedimentary microfacies.And this study indicates that Da'anzhai member of Huilong area belongs to the mixed sedimentary lake facies,including two mixed sedimentary subfacies of the shore-shallow lake and fairly deep lake,classifying five mixed sedimentary microfacies of the high-energy shell beach,low-energy shell beach,sandy shoal,shallow lake and fairly deep lake.(4)In accordance with the “flow chart” of core facies,single well facies,connected well facies and sedimentary distribution,based on thickness features of different lithology distribution and the limestone distribution of seismic facies,the sedimentary microfacies maps of Da'anzhai member are compiled.(5)Based on the characteristics of the classified mixed sedimentary facies and its evolutionary process of the Sichuan Basin and the study area of Huilong Da'anzhai member,the mixed sediment evolution model is built,which lead to a conclusion: the lacustrine mixed sedimentation of study area are mainly controlled by provenance supply and hydrodynamic condition.Owing to controlling of five types of mixed sedimentary microfacies,different Hunji rocks are formed.