Abstract: On the basis of monolayer water displacement data and mutilayers water-injection development data, analysis of basic principles of water-cut raise during water-injection development in sandstone oilfield was made by combining with the relation curve of water-cut vs. recovery percent of recoverable reserves in different oil viscosity oilfields, pointing out that high viscosity oilfield with more than 80 % of water-cut is an important stage for oilfield development. Moreover, three basic formulae for regularity of water-cut raise were compared, among which dual logarithm water displacement type curve assumed straight-line segment from low water-cut till high water-cut stages, and can be as a better formula for describing regularity of water-cut raise in oilfield.

Key words: Water-cut, Recoverable reserve, Recovery percent, Water drive, Raise velocity of water-cut