The first step in the interpretation of the SP log is the establishment of “sand” and “shale” lines, as shown in [[:file:determination-of-water-resistivity_fig1.png|Figure 1]]. These are arbitrary limits, with the sand lines normally representing the maximum deflection to the left and shale lines representing the maximum deflection to the right (in shales). Deflections to the left of the shale line are regarded as normal or negative, and correspond to porous and permeable zones containing a more saline interstitial water than the drilling mud (''R''<sub>w</sub> R<sub>mf</sub>). | The first step in the interpretation of the SP log is the establishment of “sand” and “shale” lines, as shown in [[:file:determination-of-water-resistivity_fig1.png|Figure 1]]. These are arbitrary limits, with the sand lines normally representing the maximum deflection to the left and shale lines representing the maximum deflection to the right (in shales). Deflections to the left of the shale line are regarded as normal or negative, and correspond to porous and permeable zones containing a more saline interstitial water than the drilling mud (''R''<sub>w</sub> R<sub>mf</sub>). |