Page 110 - Basic Well Log Analysis for Geologist

GAMMA RAY LOGS

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Figure 38. Chart for correcting the gamma ray index (I¢z) to the volume of shale (V,,).
Courtesy, Dresser Industries.
Copyright 1979, Dresser Atlas.
Given:
From Figure 37: GRyog = 28. GRmin = 15, and GRyay = 128. Using the formula (see text), calculate the gamma
ray index (Icg) to be 0.115.
Procedure:
1. Find the gamma ray index value (Igg) on the vertical scale on the left (in this case Igr = 0.115).
2. Follow the value horizontally to where it intersects curve 3 (representing unconsolidated, ‘Tertiary rocks) and
curve 2 (representing consolidated, older rocks). Curve | represents where Vy, = gr.
3. Drop to the scale at the bottom and read the values for the two intersections (measured in percent of shaliness).
Where [gg = 0.115, volume of shale (V,,) equals $.7% for older, consolidated rocks (curve 2) and 2.8% for
Tertiary, unconsolidated rocks (curve 3).

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