Gamma ray log

Gamma ray log measure the natural radioactivity in formations and can be use for identifying lithologies

and for correlating zones

In zones where the geologist is aware of the presence of potassium feldspars, micas, or glauconite, a

spectral gamma ray log can be run in place of the standard the gamma ray log. The spectral gamma ray

log records not only the number of gamma rays emitted by the formation but also the energy of each,

and processes that information into curves representative of the amounts of thorium (Th), potassium

(K), and uranium (U) present in the formation.

The characteristic gamma ray line that is associated with each component:

 Potassium : Gamma ray energy 1.46 MeV

 Thorium series: Gamma ray energy 2.61 MeV

 Uranium-Radium series: Gamma ray energy 1.76 MeV

If a zone has a high potassium content coupled with a high gamma ray log response, the zone might not

be shale. Instead, it could be a feldspathic, glauconitic, or micaceous sandstone.