Changes

Gamma rays tools measure the natural radioactivity of the formation. This radioactivity is emitted primarily from potassium in the structure of clay minerals, radioactive salts in the formation waters, radioactive salts bound to the charged surfaces of clay minerals, potassium associated with feldspars, and radioactive minerals associated with [[igneous rock]]s and rock fragments. The gamma ray response is used for correlation of formations between wells and for estimating volume shale and/or volume clay minerals.

Gamma rays tools measure the natural radioactivity of the formation. This radioactivity is emitted primarily from potassium in the structure of clay minerals, radioactive salts in the formation waters, radioactive salts bound to the charged surfaces of clay minerals, potassium associated with feldspars, and radioactive minerals associated with [[igneous rock]]s and rock fragments. The gamma ray response is used for correlation of formations between wells and for estimating volume shale and/or volume clay minerals.

An advanced version of the gamma ray tool, called the ''spectral gamma ray'', breaks down or segments the detected gamma rays by their different energies using spectral analysis techniques. These segments correspond to the radioactive families of potassium, uranium, and thorium. Uranium frequently occurs as a precipitated salt deposited in a formation from waters having flown through that formation. When this occurs, the uranium counts disguise radioactivity due to mineralogy. The use of the spectral tool allows the removal of gamma ray counts caused by uranium, typically permitting more accurate use of the remaining gamma rays for determining lithology, volume shale, or volume clay. In some local areas, ratios of potassium to thorium have been successfully used to determine some clay types. However, this clay typing has not proven particularly universal and should be attempted with much caution.

An advanced version of the gamma ray tool, called the ''spectral gamma ray'', breaks down or segments the detected gamma rays by their different energies using spectral analysis techniques. These segments correspond to the radioactive families of potassium, uranium, and thorium. Uranium frequently occurs as a precipitated salt deposited in a formation from waters having flown through that formation. When this occurs, the uranium counts disguise radioactivity due to [[mineralogy]]. The use of the spectral tool allows the removal of gamma ray counts caused by uranium, typically permitting more accurate use of the remaining gamma rays for determining lithology, volume shale, or volume clay. In some local areas, ratios of potassium to thorium have been successfully used to determine some clay types. However, this clay typing has not proven particularly universal and should be attempted with much caution.

Typical presentations of gamma ray measurements are shown in the logs in both [[::file:basic-open-hole-tools_fig1.png|Figures 1]] and [[:file:basic-open-hole-tools_fig2.png|2]]. (For information on the cased hole gamma ray tool, see [[Basic cased hole tools]])

Typical presentations of gamma ray measurements are shown in the logs in both [[::file:basic-open-hole-tools_fig1.png|Figures 1]] and [[:file:basic-open-hole-tools_fig2.png|2]]. (For information on the cased hole gamma ray tool, see [[Basic cased hole tools]])