Abstract：Silurian seashore sandstone is the main oil reservoir and oil-producing formation in YM34 and YM35 well blocks. The lithology and depositional setting of these two well blocks are very similar to each other, but their reservoir properties are different significantly. According to such characteristics of these two blocks as lithology, porous styles, porous architectures, physical properties and diagenesis, the reservoirs of both YM34 and 35 well blocks are composed of seashore silicarenite in no-barrier shoreland. The YM34 well block is of moderate porosity and permeability, while the YM35 well block is of extremely low porosity and permeability, with the reservoir matrix properties of the former better than those of the latter. Nevertheless, the open fractures are developed significantly in the YM35 well block, suggesting a porous fractured complex reservoir. Well test shows that both the well blocks are of high and stable deliverability. Based on the full understanding of the reservoir properties, this paper has reached the conclusion that diagenesis and tectonic activity are the main factors responsible for the differences of reservoir properties between the YM34 well block and the YM35 well block.