Abstract: Based on the production decline patterns from Daqing placanticline oilfields, it is indicated that by the end of stable production period of an oilfield, its production decline will take place in terms of hyperbolic style with n=0.5. This paper derived theoretical equations for calculating reserve production ratio and verified the rational ratio suitable for an oilfield. The proposed rational ratio should be remained to be e- qual to and greater than 9. If the ratio is lower than 9, much more rapid production decline will appear for such an oilfield.

Key words: oilfield, output, decline, reserve-production ratio, rational cutoff value