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.