Abstract:Along with development of Daqing oilfield,the amplitude and configuration of natural potential of reservoir took place large variation in comparison with that in the initial stage of development, the change of the master-slave position of diffusion absorption potential and filtration potential constituted natural potential also took place. The reasons resulted in these variations lay in sharp variation in fluid salinity and fluid pressure of reservoir after long-period water injection. The pressure state of reservoir could be judged and size of pore pressure could be precisely interpreted by using the correlation of filtration potential with differential pressure. In view of the above,it summed up a method that is suitable to interpret pore pressure of sand-stone reservoir in the later stage of water flood re covery,which is called natural potential method.