Macro drainage characters were determined by micro drainage features in pore scale. They are inhomogeneous everywhere in different directions. Three distinctive Hele-Shaw cells were designed to study the effects of pore structure on drainage process. The pore structure characters were elucidated by several parameters including pore angle

critical ratio (the ratio of the max pore diameter to the min throat size)

tortuosity and porosity. The results show that when displacement velocity is the same

larger pore angle or smaller tortuosity results in greater non-wetting phase (dodecane and hexadecane) saturation; when displacement velocity is not the same

larger displacement velocity makes greater non-wetting phase saturation. Critical ratio and porosity are not the decisive factors; their effects on drainage process are evaluated by their values and other pore structure parameters

such as pore angle and so on. When pore angle and displacement velocity are the same

smaller viscosity ratio pairs tend to have a higher drainage effect.