Which log is used to measure gamma radiation for lithology identification?

Which log is used to measure gamma radiation for lithology identification?

• A. Gamma Ray Log
• B. SP Logs
• C. Neutron Log
• D. Resistivity Log

Answer: (A)

Measuring natural gamma radiation in a borehole is used for lithology identification because different rock types emit different levels of gamma rays based on their mineral content. Rocks with clay minerals carry higher concentrations of radioactive elements (like potassium, uranium, and thorium), so they produce stronger natural gamma signals. Clean sandstones and carbonates generally emit less gamma radiation, resulting in lower readings. By recording gamma rays as counts per second, you can distinguish shale from sandstone and limestone and track lithologic changes with depth, which is exactly what lithology identification relies on. Other logs look at different properties: spontaneous potential responds to electrochemical contrasts and helps with bed boundaries and whistle-zone indications, but it doesn’t directly measure gamma radiation. Neutron logs gauge hydrogen content to estimate porosity, and resistivity logs measure how strongly rocks resist electrical current to infer fluid type and saturation. Those provide porosity or fluid information, not the natural gamma signature used for lithology.

Measuring natural gamma radiation in a borehole is used for lithology identification because different rock types emit different levels of gamma rays based on their mineral content. Rocks with clay minerals carry higher concentrations of radioactive elements (like potassium, uranium, and thorium), so they produce stronger natural gamma signals. Clean sandstones and carbonates generally emit less gamma radiation, resulting in lower readings. By recording gamma rays as counts per second, you can distinguish shale from sandstone and limestone and track lithologic changes with depth, which is exactly what lithology identification relies on.

Other logs look at different properties: spontaneous potential responds to electrochemical contrasts and helps with bed boundaries and whistle-zone indications, but it doesn’t directly measure gamma radiation. Neutron logs gauge hydrogen content to estimate porosity, and resistivity logs measure how strongly rocks resist electrical current to infer fluid type and saturation. Those provide porosity or fluid information, not the natural gamma signature used for lithology.