Abstract: Based on stable flow velocity model with equal production one source and one gathering and analysis of maximum pressure gradient field, relationship between starting pressure gradient and injection-production differential pressure and producer-injector spacing is presented. And using starting pressure gradient vs reservoir permeability, the cutoff permeability suitable for effective waterflooding of reservoir under different injection-production conditions is given. The theoretical and practical results are generally identical, indicating its good practicability, which can be as a guide for effective development of low permeability oilfield.

Key words: low permeability reservoir, pressure gradient, spacing, cutoff permeability