Abstract: In accordance with one dimensional waterflood theory of Buckley-Leverett,mathematical relationship between oildisplacement efficiency and recovery percent of recoverable reserves as well as minimum value of displacement efficiency arederived. And the numerical model of this relationship from a case of Liaohe field is developed accordingly. In addition, using therelationship among recovery percent,displacement and volumetric sweep efficiency, the equations for estimation of the volumetricsweep efficiency and the recovery percent of recoverable reserves are obtained, based on which the volumetric sweep efficiencyand the potential analysis of displacement efficiency in late stage of waterflooding along with development regime to be adoptedare proposed. The actual application is identical to the calculated results.

Key words: water flood, oilfield development, volumetric sweep efficiency, displacement efficiency, mathematical model