Abstract: Determination of rational injection-production well spacing is significant for economic and effective exploitation of low permeability oilfield or reservoir due to existence of starting pressure gradient and recovery difficulty. Based on theory of fluid flow mechanics, the pressure gradient distribution equation between injector and producer under unequal production rate is deducted, by which the change of driving pressure gradient with well spacing under available injector-producer conditions can be determined. Study shows that such a relationship between injector and producer is not established until the driving pressure gradient completely overcomes the starting pressure gradient of reservoirs. Hence, the injection-production well spacing corresponding to the minimum driving pressure gradient in overcoming the maximum starting pressure gradient should be a proper maximum injection-production well spacing that the pay zone can be effectively produced. Well block Shu-322 in Yushulin oilfield is taken as an example integrated with starting pressure gradient and permeability, the relationship between the maximum injection-production well spacing and reservoir permeability is set up, showing that the effective producing maximum well spacing should be 242 m compared with 300 m available now. This is more reliable basis to be used for next-step modification of the oilfield development.

Key words: low permeability reservoir, well spacing, pressure gradient, Yushulin oilfield