Abstract:

On the basis of microscopic characteristics research of E₁f₃ reservoir in Shanian oilfield, oil displacement efficiency has been measured by the authentic sandstone micro-model experiment. Influences of physical properties and pore structure on oil displacement efficiency have been studied, and the special phenomenon of samples which have similar permeability but great different oil displacement efficiencies has been explained. Furthermore, the accuracy of mercury-withdrawal efficiency which is used as oil displacement efficiency has been analysised. The result shows that the rock of the reservoir is fine pore-throat and strong anisotropy, which mainly is due to the fine grain-size, poor sorting, high-content interstitial matter and high compaction. Oil displacement efficiency increases as the physical properties become better and the throats become larger, but it has a complex relationship with throatsorting: large throat intensifies the heterogeneity between throats while it provides good connective channels among pores, and small throat ensures the uniform propulsion of the injection water. Oil displacement efficiency is mainly controlled by physical properties and the max connective throat, and it has a good correlation with mercury-withdrawal efficiency while they are different in the low-value zone.

Key words:  pore structure, displacement efficiency, anisotropy, low-permeability reservoir, Shanian oilfield, Subei basin