Keywords: 
• oil displacement efficiency /
• reservoir's heterogeneity /
• micromodel

Abstract: Reservoir's recovery percentage of oil is equal to the injected water's swe eping efficiency in macro and the oil displacement efficiency of the injected w ater in micro. So the final reservoir's recovery percentage of oil can be affected by the oil displacement effecency. Ansai oilfield is a typical low permeability oilfield. It's reservoir is Yanchan g formation of Triassic system,and the oil is mainly reserved in Chang6 reservoir of Yanchang ormation.Pingqiao and Wangyao are located in the north and the sou th of Ansai oilfield.The study about the oil displacement efficiency of Chang6 r eservoir in the two areas has practical significances. According to the study it can be seen that the differenct petrologic feature leads to the difference in pore structure and petrophysical property between the two areas under the later diageneses. The results are that the heterogeneity of pore structure in Pingqiao is more serious than in Wangyao,and the petrophysical property in Wangyao is better than in Pingqiao. The natural sandstone micromodels are made with sampled cores.Using the micromod els,the displacement experiments of oil and water have been done. Experimental results indicate that oil displacement efficiency of the Chang6 reservoir in Wang yao (40.34%) is higher than in Pingqiao (30.48%). The difference of pore structu re, especially the difference of heterogeneity of pore structure is the reason that leads to the great difference of oil displacement efficiency between Wangyao and Pingqiao.