The procedure to determine ''R''<sub>w</sub> from the SP is outlined as follows. The data required include the SP, the invaded zone resistivity, the formation temperature, and the mud and mud filtrate resistivities at the given formation temperature. | The procedure to determine ''R''<sub>w</sub> from the SP is outlined as follows. The data required include the SP, the invaded zone resistivity, the formation temperature, and the mud and mud filtrate resistivities at the given formation temperature. |