Analysis On Sequence And Sedimentary Of Jurassic And Main Controlling Factors In Sikeshu Sag,Junggar Basin

Sikeshu Sag is located in the southwest of Junggar Basin,which belongs to the piedmont depression of North Tianshan.Over the past decade,corresponding exploration work has been carried out in Chepaizi uplift and Changji sag around Sikeshu Sag.It has been proved by practice that there are abundant oil and gas resources in the southwest of Junggar Basin.Therefore,the systematic study of Sikeshu Sag has important exploration value.Sequence architecture and development characteristics of sedimentary facies in Sikeshu Sag can provide reliable evidence for hydrocarbon prediction,while the distribution of sequence,types of sedimentary body and accumulation styles are influenced by paleotopography.Therefore,to make full use of the seismic section and drilling data in the study area,and the analysis of sequence stratigraphy and sedimentary system on the basis of the study of regional fault system and slope break zone distribution is the key to establish the genetic model of sand bodies in the study area and to inspire exploration ideas.Through accurate horizon tracing and fine structural interpretation of several twodimensional seismic section in the study area,it is found that there are three EWtrending fault systems in the study area,namely,the Aika fault zone,the Aikanan fault zone and the Guertu fault zone.There are three sedimentary slope breaks zone nearly EW-trending and controlled by three fault,namely,the Aika slope break zone,the Aikanan slope break zone and the Guertu slope break zone.By identifying various reflection configuration of seismic section,This paper clarifies the this paper clarifies the distribution law of provenance in the west and sequence distribution laws of Jurassic study area.It considers that the Jurassic consists of four third-order sequences,corresponding to four formation,each sequence is dichotomous,consisting of the bottom lacustrine transgressive system tract and upper lacustrine regressive system trace.The faults in the study area control the distribution of the Jurassic secondary and tertiary sequence boundaries.Through core observation and thin section identification in the study area,three types of sedimentary facies,alluvial fan facies,fan delta facies and lacustrine facies,are determined.They are subdivided into four types of sedimentary subfacies and ten kinds of sedimentary microfacies.Seismic facies characteristics are analyzed by seismic section,single well sedimentary facies is analyzed by combining logging curves,and the “Fan delta facies-lacustrine facies” sedimentary facies pattern from west to east is analyzed by synthesizing data of provenance,slope break zone and seismic attributes.The distribution of fault system and provenance in the study area are the dominant controlling factors of sedimentary facies distribution.Finally,based on two-dimensional seismic data and the data of well logging and cores,two types of sand body genesis models are analyzed,which are "ravine-fan" sedimentary system and "large-scale foreset sand body-turbidite fan" sedimentary system controlled by EastWest slope break zone.