Page 50 - Basic Well Log Analysis for Geologist

THE SPONTANEOUS POTENTIAL LOG

Figure 12. Chart for finding SP Correction Factor used to correct SP to SSP (see exercise, Fig. 11).

Courtesy, Dresser Industries.
Copyright 1975, Dresser Atlas.
Defined:
R; = shallow resistivity
R,, = resistivity of drilling mud at formation temperature
Example:
R,/R,, = 30
Bed Thickness = 8 ft

Procedure:
1. Locate a bed thickness on the vertical scale (in this case 8 ft).
2. Follow the value horizontally across until it intersects the R,/R,, curve (in this example Rj/R,, = 30. so point
will be to the right of the 20 curve).
ae . Drop vertically from this intersection and read the SP correction factor on the scale across the bottom (in this
example, a value of 1.3).
4, Multiply SP by the SP Correction Factor to find SSP.

For the exercise in Figure | 1:
SSP = SP x Correction Factor
SSP = —40mv X 1.3 (—40mv is SP value taken at 7,446 ft. see Fig. 11)
SSP = —S2inv

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