Abstract: Based on the core data and well logs from over 250 wells in studied area, the rock type and assemblage, mineral composition, deposi-tional pattern, structure, log facies, biologic fossil and grain size feature are studied, by which it is confirmed that the underwater distributary channel microfacies, mouth bar microfacies and complex sandbodies which are cut and superimposed by the underwater distributary channels at mouth bar in Chang-6 formation of delta front in AS area could be as the favorable facies for forming the main reservoir body. The specific de-scriptions of the indiv idual microfacies type, composition, characteristic, distribution and corresponding favorable areas were made, thus point-ing out that the well developed underwater distributary channel and mouth bar in Chang-67 member allow their processes to better controls of continuous distribution and range of the major oil-bearing zone in this area.

Key words: Erdos basin, low permeability, reservoir, sedimentary facies