Question

Which ONE of the following rocks shows the highest reading in the natural gamma ray log?

• A. Dolomite
• B. Anhydrite
• C. Oil Shale
• D. Limestone

Hint:

Oil shale typically shows high gamma ray readings due to its organic content and the presence of radioactive elements like uranium.

Answer 1

The Correct Option is C

Natural gamma ray logs measure the natural radioactivity of rocks, primarily due to the presence of potassium, uranium, and thorium. Among the listed rocks, {Oil Shale} typically has the highest gamma ray reading because it contains high concentrations of radioactive elements, especially uranium. 
- Dolomite generally has lower gamma ray readings as it is a carbonate rock with fewer radioactive elements. 
- Anhydrite also typically has lower gamma ray readings compared to oil shale. 
- Limestone contains low levels of natural radioactivity as well, contributing to a relatively lower gamma ray response. 
Thus, the correct answer is C, Oil Shale.