Abstract: Sedimentological principles and investigation approaches were combined with thin sections, scanning electron microscope data on the study of tight sandstone reservoir diagenetic facies in Donghetang formation, Bachu area.The result dictates that reservoirs of the formation were shaped by 6 diagenesis effects but only three of which, namely compaction, cementation and dissolution, had played most part.The Formation was determined to be in an A-B stage of middle diagenesis phase.Based on four parameters (apparent compaction rate, apparent cementation rate, apparent dissolution rate, amount of dissolution) and asphalt-filling of the formation, we recognized seven kinds of diagenetic facies in the formation contains, including medium compaction and cementation with strong dissolution facies (Ⅰ), medium compaction and cementation with medium dissolution facies (Ⅱ), medium compaction and cementation with weak dissolution facies (Ⅲ) and etc., among which, type I to Ⅲ are considered facies with exploration potentials.Relevant log data and the k-nearest neighbor classification method were also used to differentiate continuously and automatically the diagenetic facies of layers penetrated by 17 wells in the research area.The result shows that the upper Formation is dominated by type Ⅵ facies, with the most favorable facies occurring in Ga2-Yu2-Ba5 and Qun6-Bakai8-Batan4-Kangtan1 wellblocks, and the lower part is more developed than the upper one and dominated by type Ⅱ facies, with the most favorable facies occurring in Ga2-Qun6-Bakai8-Ba2-Kang1 wellblock.The study may serve as a geological basis for high-quality reservoir prediction.

Key words: diagenetic facies, diagenesis, tight sandstone, Donghetang Formation, Bachu area