Lecture-10(welllog-gamma)

Lecture-10(welllog-gamma) - A Well Log Example Lecture - 11...

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A Well Log Example Lecture - 11
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Nuclear Logs Gamma Ray Logs Measure of natural radioactivity of the formations Gamma rays are bursts of high-energy electromagnetic waves spontaneously emitted by radioactive material (potassium, uranium and thorium) in rocks Radioactive material predominantly in shales. Why? The lattice structure of clay materials has holes (gaps) that are occupied by radioactive material Shales have very low permeabilities – little possibility of radioactive material getting washed out Clays have igneous origin – more likely to be radioactive Sandstones have quartz origin that have very tight lattice and cannot accommodate radioactive material
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Gamma-ray can be used to compute volume proportion of shale at any vertical location along the well: 1 Calculate γ -ray index: 2 Read volume of shale V sh from chart 3 curves in the chart: 45 o line – upper bound regardless of formation, line 2 – older (pre-tertiary rocks – more dense), line 3 – sand clean shale sand clean GR GR GR GR GR I - - = - = 1 2 083 . 0 7
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Lecture-10(welllog-gamma) - A Well Log Example Lecture - 11...

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