بسم الله الرحمن الرحيم

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

Abstract 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.

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.

GAMMA –RADIATION 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 cm, equivalent to frequencies ranging from to sec -1.

The energy is expressed in electron-volts (eV). The energies of gamma rays are of the order of the MeV (l0 6 eV). Usually, the α, β and γ-emissions are simultaneous, figure (1). β- and α -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.

Potassium-Bearing Minerals and Rocks 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.

Uranium-Bearing Minerals and Rocks 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.

Thorium-Bearing Minerals and Rocks 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.

NATURAL GAMMA RAY LOGS 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.

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: m and max. GR value=27 API Depth interval: m and max.GR value=25 API Depth interval: m and max.GR value=23 API Depth interval : m and max. GR value=26 API Depth interval: m and max. GR value=21 API Depth interval : m and max.GR value=51 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.

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.

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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