Editing Well logging (section)

====Resistivity log====
{{See also|Resistivity logging}}
Resistivity logging measures the subsurface electrical resistivity, which can impede the flow of electric current. This helps to differentiate between formations filled with salty waters (good conductors of electricity) and those filled with hydrocarbons (poor conductors of electricity). Resistivity and porosity measurements are used to calculate water saturation. Resistivity is expressed in ohms·meter (Ω⋅m), and is frequently charted on a logarithm scale versus depth because of the large range of resistivity. The distance from the borehole penetrated by the current varies with the tool, from a few centimeters to one meter.