Abstract: Many scholars have made detailed studies and discussions on the types of sedimentary facies in the Shawan Formation, the major oil-generating formation in the Chunguang block, but their achievements and recognitions are inconsistent. On the basis of outcrop section and drilling core observation, together with the rock color, sedimentary structure and other facies markers, it is derived that the Shawan Formation is of the braided river delta-lake sedimentary system. According to shapes of wireline logging curves and seismic attribute analysis, the sedimentary microfacies are identifed as braided channel, and underwater distributary channel at the braided river delta front. Statistical analysis on the features of lithologic traps at the oil-producing point indicate that the underwater distributary channel sands at the braided river delta front serve as the major reservoir, and the depositional pattern is summarized as the underwater distributary channel sands at the braided river delta front as reservoir with lateral phase-transition seal. According to this pattern, the prospective targets are selected within the study area, and the underwater distributary channel sands at the braided river delta front in S2 sand group of Shawan Formation within the study area is considered as Type I target zone for the following exploration.

Key words: lithologic reservoir, Shawan Formation, Chunguang block, Junggar Basin, underwater distributary channel, braided river delta