Detecting The Radioactive Minerals Using Well Logs Methods

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• Detecting The Radioactive Minerals Using Well
  Logs Methods
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• Asst. Professor Dr. Mahmoud A. AL-Mufarji
• Asst. Professor Dr. Jawad R. AL-Assal
• Asst. Lecturer Adnan A. Abed AL-Jabbory

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• Abstract
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• Radioactivity is accompanied by the emission
  of alpha or beta particles, gamma rays. Gamma
  rays are electromagnetic radiations emitted from
  an atomic nucleus during radioactive decay. The
  clay minerals are primarily responsible for two
  sources of radioactivity, potassium, and thorium,
  associated with most shales.
• There are two types of GR logs. One, the standard
  GR log, measures only the total radioactivity.
  The other, the NGS (Natural Gamma Ray
  Spectrometry) log, measures the total
  radioactivity and the concentrations of
  potassium, thorium, and uranium producing the
  radioactivity.

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• We apply the gamma ray log in some wells in south
  Iraqi field normally reflects the shale content
  of the formations. This is because the
  radioactive elements tend to concentrate in clays
  and shales. Thus, as shale content increases the
  gamma ray log response increases also.
• When we are correlating density log and gamma ray
  log for two wells in this study and Showing for
  maximum gamma ray reading as a maximum reading in
  density log because The original density tool
  consisted of a high-energy gamma ray emitting
  source coupled with a shielded gamma ray
  detector.

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• GAMMA RADIATION
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• Gamma-radiation may be considered as an
  electromagnetic wave similar to visible light or
  X-rays, or as a particle or photon. Gamma rays
  are electromagnetic radiations emitted from an
  atomic nucleus during radioactive decay. These
  radiations are characterized by wave lengths in
  the range of 1 0 -9 - 1 0 -11 cm, equivalent to
  frequencies ranging from 1019 to 1021 sec -1.

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• The energy is expressed in electron-volts (eV).
  The energies of gamma rays are of the order of
  the MeV (l06 eV). Usually, the a, ß and
  ?-emissions are simultaneous, figure (1).
• ß- and a -particles do not penetrate far enough
  to be detected by logging techniques. The gamma
  rays have a very high power of penetration and
  can be detected and recorded in present-day hole
  conditions. For that reason, they are the basis
  of several important logging techniques.
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• Potassium-Bearing Minerals and Rocks
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• The source minerals of potassium are the
  feldspars and micas plus a large number of
  minerals of minor importance.
• During alteration, some silicates such as the
  feldspars are completely dissolved the potassium
  is thus liberated in ionic form and transported
  in solution Micas, on the other hand, may lose
  only part of their potassium during alteration,
  the remainder staying in the crystal lattice.

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• Uranium-Bearing Minerals and Rocks
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• The source minerals are in igneous rocks of
  acid origin. Table (1) lists the average content
  (in ppm) of uranium and thorium in several rock
  types. These are averages actual values can vary
  considerably.

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• Thorium-Bearing Minerals and Rocks
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• Thorium originates from igneous rocks of the acid
  and acido-basic types (granites, pegmatites,
  syenites, nepheline syenites).
• Table (1) lists the average concentrations (in
  ppm) encountered.

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• NATURAL GAMMA RAY LOGS
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• The natural gamma ray (GR) log is a recording
  of the natural radioactivity of the formation.
  There are two types of GR logs. The standard GR
  log which measure only the total radioactivity.
  and NGS (Natural Gamma Ray Spectrometry) log
  which measure the total radioactivity and the
  concentrations of Potassium, Thorium, and Uranium
  producing the radioactivity.

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• METHODOLOGY AND RESULTS
• The results are shown in Fig. (4) for some well
  in the xx field, using Petrel program to read the
  maximum value of Gamma ray. As noticed, gamma ray
  reading reached maximum value in six depth
  interval
• Depth interval 2288.66-2306.5 m and max. GR
  value27 API
• Depth interval 2310.67-2320.8 m and max.GR
  value25 API
• Depth interval 2375.88-2421.16m and max.GR
  value23 API
• Depth interval 2178.2-2183.37m and max. GR
  value26 API
• Depth interval2221.2-2233.8m and max. GR
  value21 API
• Depth interval 2330.16-2338.94 m and max.GR
  value51 API
• From these intervals the gamma ray log normally
  reflects the shale content of the formations.
  This is because the radioactive elements tend to
  concentrate in clays and shales. Thus, as shale
  content increases the gamma ray log response
  increases also.

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• Fig.(5) showed the correlation between gamma log
  and the density log, it appeared that the maximum
  reading of the gamma ray corresponding to maximum
  reading of the density log at the same depth
  because the original density tool consisted of a
  high-energy gamma ray emitting source coupled
  with a shielded gamma ray detector.

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• RECCOMEDATION
• Using the most sophisticated software in
  interpretation in gamma ray reading to detect the
  radioactive minerals
• Using the natural gamma ray spectral (NGS log)
  rather than standard gamma ray.
• In oil well drilling it is recommended to examine
  the cutting from radioactivity.

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• Thank you