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A common gamma-ray log records the total radiation and cannot distinguish between the radioactive elements, while a spectral gamma ray log (see below) can. For standard gamma-ray logs, the measured value of gamma-ray radiation is calculated from concentration of uranium in ppm, thorium in ppm, and potassium in weight percent: e.g., GR API = 8 ...
Measurement of natural emission of gamma rays in oil and gas wells are useful because shales and sandstones typically have different gamma ray levels. Shales and clays are responsible for most natural radioactivity, so gamma ray log often is a good indicator of such rocks. In addition, the log is also used for correlation between wells, for ...
Thus the presence or absence of gamma rays in a borehole is an indication of the amount of shale or clay in the surrounding formation. The gamma ray log is useful in holes drilled with air or with oil based muds, as these wells have no SP voltage. Even in water-based muds, the gamma ray and SP logs are often run together.
Federal and state nuclear regulatory agencies keep records of the radionuclides used. [ 4 ] As of 2003 the isotopes Antimony-124 , argon-41 , cobalt-60 , iodine-131 , iridium-192 , lanthanum-140 , manganese-56 , scandium-46 , sodium-24 , silver-110m , technetium-99m , and xenon-133 were most commonly used by the oil and gas industry because ...
The first gamma ray source to be discovered was the radioactive decay process called gamma decay. In this type of decay, an excited nucleus emits a gamma ray almost immediately upon formation. [note 1] Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium.
The gamma ray log is particularly useful as shale beds which often provide a relatively low permeability cap over hydrocarbon reservoirs usually display a higher level of gamma radiation. These logs were important because they can be used in cased wells (wells with production casing). WSI quickly became part of Lane-Wells.
Density logging is a well logging tool that can provide a continuous record of a formation's bulk density along the length of a borehole.In geology, bulk density is a function of the density of the minerals forming a rock (i.e. matrix) and the fluid enclosed in the pore spaces.
Gamma ray emission follows the previously discussed modes of decay when the decay leaves a daughter nucleus in an excited state. This nucleus is capable of further de-excitation to a lower energy state by the release of a photon.