Definition - What does Resistivity Log mean?
A Resistivity Log is a detailed record of the resisting power of a formation rock to the flow of an electric current. As hydrocarbons do not conduct electricity like water, resistivity is measured and logged to characterize whether the rock formation contains hydrocarbons or is filled with water. Resistivity log also helps in the evaluation of the rock formation type. The unit of rock resistivity is ohm-m and it is presented on a logarithmic scale.
Petropedia explains Resistivity Log
Resistivity logs are useful in hydrocarbon exploration. Resistivity logging is a well logging record that is used to measure the resistivity of a rock formation to conduct electricity. The data that is obtained after resistivity logging is carried out, is recorded on a resistivity log. This log helps in characterization of the rock sediment. The data recorded on the resistivity logs shows how the rock formation opposes an electric current. There is a large difference in the resistivity to conduct electricity through a rock formation filled with hydrocarbons and one that is filled with water and this helps in characterization of the rock formations. If a rock formation contains hydrocarbons its resistivity to electric flow will be high, while if it contains water it's resistivity will be low.