Spontaneous potential is the potential resulted from formation's electrochemical reaction under non polorization state

and its scale is determined by the density of formation water ions and the cation exchange capacity.The density of formation water ions and the capacity of cation exchange of each layer could be calculated according to spontaneous potential curve and polarizability curve of induced polarization log

and the formation water resistivity could be calculated.In addition

the oil saturation of argillarceous sandstone reservoir could also be calculated by using W-S model.Through large amount of core tests

geological interpretation parametres suitable for this area are obtained but remain to be determined.Actural hydrocarbon exploration results proved that the electrochemic log interpretation model is well coincident with practical geological condition.