Meander-braided transition features and hydrocarbon accumulation characteristics in Neogene Shawan Formation, Chunguang exploration block, Junggar Basin

The Chunguang exploration area is one of the important oil-gas bearing blocks on the northwestern margin of Junggar Basin. Considerable number of high-yield wells have been developed in the Neogene Shawan Formation during the earlier exploration stage, and great exploration and development potential in this area were indicated. In order to meet the needs of delicate exploration, a further study of the sedimentary characteristics, sedimentary evolution and reservoir forming models were promising for the further exploration. With the analysis of cores, loggings and amplitude slices, the typical sedimentary microfacies of diara and point bar deposits were identified in the study area. Then it was considered that braided river and meandering river deposits were developed in the study area with the feature of "braided river deposits in the east part of study area and meandering river deposits in the west part". Moreover, the sedimentary evolution process was determined and a new sedimentary model was established. With the flattening of terrain, the continuous rising of base level, the weakening of provenance supply and the changing of climate from humid to heat, the sedimentary system was gradually transformed from braided river deposits to meandering river deposits. By the study of reservoir accumulation and recognition characteristics of different river-type deposits, a new reservoir forming model was built. Combined with the understanding of reservoir formation, the favorable exploration direction was indicated, the exploration field was effectively expanded, and good exploration results were obtained, which provided theoretical support for the increase of reserves and production in the Chunguang exploration area.