 For brine-saturated intervals (formula_14) Archie's law can be written

Hence, plotting the logarithm of the measured in-situ electrical conductivity against the logarithm of the measured in-situ porosity (Pickett plot), according to Archie's law a straight-line relationship is expected with slope equal to the cementation exponent formula_6 and intercept equal to the logarithm of the in-situ brine conductivity.Archie's law postulates that the rock matrix is non-conductive.For sandstone with clay minerals, this assumption is no longer true in general, due to the clay's structure and cation exchange capacity.