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. . <br /> <br />radiation observed in sedimentary rocks. Each of these elements, naturally, emits gamma <br />rays that aze distinctive in both count rate and energy. <br />In sedimentary formations the Gamma Ray normally reflects the shale content of the <br />formations (shales and clays generally contain some Potassium or Thorium). Clean <br />formations (limestone, dolomite) usually have very low levels of radioactivity unless the <br />formation or its waters contain potassium salts. <br />Gamma ray logs are now calibrated in API units. Anhydrite or salt corresponding to a few <br />API units and shales up to 200 or more API units. <br />The depth of investigation is approximately one foot into the formation. Corrections have <br />to be applied for hole conditions (hole size, mud weight, casing) as any material between <br />the counter and the formation will absorb gamma rays. <br />Uses of the Gamma Ray Log <br />l) shale bed definition and volume of shale <br />2) formation correlation <br />Spectralog® <br />The Spectralog is similar to a conventional gamma ray, Lke a gamma ray it measures the <br />total naturally occurring ganmrna ray radiation. However, It also breaks down potassium <br />(K), uranitun ([J) and thoritmm (Th) into parts per million or a percentage of the total <br />gamma ray count. <br />This is very useful in either qualitative or quantitative analysis of complex formations. It <br />can aid in stratigraphic correlation, matrit identification, high permeability and fracture <br />identification. Quantitatively, data measured by the Spectralog include, reservoa shaliness <br />detemmination, source rock characterization of azgillaceous formations and evaluation of <br />potash and uranium deposits. <br />23 <br /> <br />