Gamma ray logging is a process used to measure naturally-occurring radioactivity below the soil. As certain types of rocks break down over time, they emit radiation in the form of gamma rays. There is a high correlation between gamma ray activity and deposits of sediment-rich rocks and clay called shale. The presence of shale often serves as a solid indication that oil and natural gas can be found nearby. Gamma ray logging can also be used in some mining and water drilling operations.
During gamma ray logging, geologists start by drilling a deep bore hole to access areas well below the surface of the earth. To save money, these crews may also use existing bores and wells to complete gamma ray testing. Next, they lower a cesium or sodium iodide probe down below the surface using cables or ropes. The probe measures gamma rays at different depths, generally every few feet or meters. Oil and mining crews use the data generated during this process to find the best locations and depths to drill for oil and other fuels.
Depending on the scope of the operation, geologists and other crews can choose from two gamma ray logging techniques. Common logging provides only an indication of radioactivity, but does not distinguish between different types. Spectral gamma ray logging measures the wavelength of each gamma ray to identify different types of radiation. Typically, spectral logging procedures can measure amounts of potassium, thorium, and uranium separately. This allows mining and drilling crews to search for specific materials that are associated with each of these types of radioactivity.
In addition to using this technology to find oil and gas deposits, geologists may also utilize gamma ray logging for a number of additional functions. This process can be used to map the layers of the earth, and to determine soil makeup. It can also be used to find certain minerals, metals, and other goods so they can be mined from the earth. In some cases, gamma ray logging can also be used to find safe areas to drill water wells so they are free from radiation.
Gamma ray logging represents one of many logging methods used to explore the area below the soil. Compared to alternate methods, however, it offers a number of advantages. The probe used in gamma ray logging is able to read radioactive waves through the walls of a pipe or casing, while other devices can't work through these structures. Gamma ray probes also represent an economical and easy-to-use method of exploring deep below the soil without the need to invest in more expensive equipment.