Velocity sensitivity in the Ed3 reservoir of Gaonan area results from the migration of kaolinite distributed in pores. As the length and diameter of kaolinite are dominantly larger than the throat diameter, the velocity sensitivity becomes increasingly lower in samples with the lowering clay matrix content and gets higher and higher with the increasing clay content. Calcite cement is mainly distributed in rock pores of the reservoir, and minor cement and clay mineral matrix are distributed in the throat, indicating that earth acid rather than hydrochloric acid is more effective in acidification. Due to the extensive existence of secondary enlarged quartz in throat, strong alkali drilling fluid may somewhat help to improve the reservoir permeability. However, as the critical value of pH is about 7.7 which results in the secondary precipitation, and the flowing back of the drilling fluid is difficult, the alkalinity of drilling fluid should be taken into account during the drilling process. Montmorillonite and illite/montmorillonite are different greatly in content in different positions, which determines the difference of salt sensitivity in the reservoir.