Abstract: Basing on the origin of the spontanous electric field in the well,technological process of SP logging and the similarity theory of the simulated experiment,thispaper obtains the theoretical basis of part space physical model. According to the theory, a simulated exper-iment device is designed and made,and a series of tests are done in different conditions. In
the end,the relation of SP to such factors as formation resistivity invasion radius,forma-tion water-out degree is obtained,and a contrast analysis of experiment results,numerical simulation and practical data is given in this paper as well.

Key words: SP, Simulated experiment, Invasion radius, Electric field, Physical model