Abstract: The Upper Jurassic Qigu Formation in Area-A within the hinterland of Junggar Basin is a hotspot for oil and gas exploration in recent years.Numerous wells have achieved high-yield oil and gas flows,demonstrating significant potential for oil and gas resources.In light of the sedimentary system of the shallow water delta front in the Qigu Formation,the controlling factors and patterns of favorable sand body distribution remain unclear.Based on the data of core,logging,seismic,heavy minerals and trace elements,the sedimentary characteristics of the shallow water river-controlled delta in the Qigu Formation within the study area are investigated.The study reveals that the river-controlled shallow-water delta is formed in a sedimentary environment characterized by multi-source supply,a shallow water body,frequent oscillations,and a medium hydrodynamic force.The predominant sand body type is mainly the river-bar complex,and the rock is generally oxidized.Based on the thickness,particle size and bedding scale of gravel,the river dam complex is categorized into three types:main channel+residual mouth bar,branch channel+residual mouth bar and residual mouth bar.Among them,the branch channel+residual mouth bar and the river dam complex dominated by residual mouth bar constitute favorable sand bodies.Their distribution is mainly governed by the variation of base level,the influence of river channel supply,ancient landform,river and wave.Favorable sand bodies are vertically distributed in the middle section of the base level rise;on the plane,they are distributed in the slope area and platform area at a moderate distance from the main channel.The research outcomes have deepened the investigation of the sedimentary characteristics of river-controlled shallow-water delta,offering a foundation for the subsequent optimization of the zone and also furnishing a reference for similar blocks.

Key words: river-controlled shallow-water delta, sedimentary environment, sand body type, sedimentary model, Junggar Basin