Abstract: Both of Wan Jiye's extra-protruding curve and Bridge's curve belong to bilogarithmic water-drive characteristic curves with similar function, which are major methods for waterflood oilfield development evaluation. Because of lacking theoretical deducing, these curves have been ignored by reservoir engineers for a long time. Following the research thoughts of the literature [1], combining Welge's equation with material balance equation, this paper presents two types of average water saturation functions and exit-end water saturation function, and then gives the theoretic deducing process of above two curves and individual corresponding percolation expressions to oil and water. This study provides both in-depth recognition of above two curves and credible theoretic basis for their popularization.

Key words: water-drive characteristic curve, logarithm, theory, method, derivation