Gamma ray tool

Drilling Fluids & Logging

The Gamma Ray (GR) tool measures naturally occurring gamma radiation emitted by rock formations. Since shales typically contain higher concentrations of radioactive isotopes (like Potassium, Uranium, and Thorium) compared to sands or carbonates, the GR log is the primary tool for lithology identification and correlation.

In the oilfield, the GR log is the 'baseline' log used to distinguish between reservoir rock (low gamma count) and non-reservoir rock (high gamma count). It is standard on almost every LWD and wireline run and is essential for depth matching between different logging runs.