Sedimentary characteristics and sedimentary model of the Upper Permian-Lower Triassic shallow braided river delta in the hinterland of the Junggar Basin

Abstract

The lower play of the Junggar Basin has huge oil and gas potential, which is the most important strategic succession field for oil and gas exploration. Large-scale delta sand bodies are developed in Permian and Triassic in the four sags in the hinterland, in which new discoveries of oil and gas have been made in succession. In order to reveal the sedimentary characteristics, sedimentary model, and distribution patterns of sand bodies in the hinterland, the studies on basin prototype, sequence framework, paleogeomorphic restoration and sedimentary system were systematically carried out based on a large number of newly drilled cores, logging and geophysical data. The results show that: the development background of large depression lake basin can be identified in the development period of the Upper Permian-Lower Triassic shallow water braided river delta in the hinterland of the basin, and the study area has the characteristics of flat terrain, small slope, sufficient material supply, extremely shallow and frequently turbulent water bodies, alternating oxidation and reduction environments, and overall oxidation environment during the sedimentation period. The shallow braided river delta is characterized by coarse grain size, low impurity content, medium texture maturity, long distance transportation, strong hydrodynamic scouring, cross bedding and parallel bedding. The advantageous water system in the sedimentation period of the Upper Wuerhe and Baikouquan formations in the hinterland mainly comes from the northwest and northeast, and extends from north to south as a whole, with three provenance systems developed, namely Wuerhe provenance, Karamay provenance and Kelameily provenance. The terrain within the basin has obvious zoning characteristics, forming four facies belts namely fan delta area, braided river delta plain area, front area and lake area, thus forming a shallow water braided river delta sedimentary pattern of "large plain, small front" in the hinterland, where plain area and front area are favorable sand body development zones.

Keywords

• shallow water braided river delta
• sedimentary model
• upper wuerhe formation
• baikouquan formation
• upper permian
• lower triassic
• hinterland of junggar basin