Calculation on a reasonable production/injection well ratio in waterflooding oilfields

According to the accurate definition of the reasonable production/injection well ratio and injection/production ratio for waterflooding oilfields, the formula of the reasonable production/injection well ratio under the same or different formation pressures between oil well and injection well is derived based on the principle of extreme value. The formula can be used in the balanced or unbalanced injection/production system such as reservoirs in high water cut stage or low/permeability reservoirs. All the previous formulas have flaws: the method of “injectivity, productivity indexes” is based on balanced injection/production system; the method of “injectivity, productivity indexes and injection/production ratio” ignores the influences of crude oil properties; and there is no theoretical and practical significance in the method of “injectivity index to liquid productivity index ratio and injection/production pressure difference”. The method presented in this paper is applied and verified in the Chaoyanggou Oilfield of Daqing. The daily fluid rate of the oilfield can reach the maximum value of 5 155.8 t at the reasonable production/injection well ratio of 3.28. Key words: waterflooding, injection/production ratio, reasonable production/injection well ratio, injection/production equilibrium, low-permeability reservoi