Page 94 - Basic Well Log Analysis for Geologist

POROSITY LOGS

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Figure 30. Chart for correcting Sidewall Neutron Porosity Log (SNP*) for lithology. Note: this is a Schlumberger example: do not
use this chart with another type neutron log (see text).
Courtesy. Schlumberger Well Services.
Copyright 1969, Schlumberger.

Given: The lithology is dolomite. Also. the apparent limestone porosity is 15%. The value for apparent limestone
porosity is read directly from a Sidewall Neutron Porosity Log (SNP*). A Sidewall Neutron Log (SNP*) is not
shown here; instead the value is given to you.

Procedure:
1. Find the value for apparent limestone porosity (read from an SNP* fog) along the scale at the bottom of the
correction chart. In this example. the value is 15%.
bo Follow the value vertically until it intersects the diagonal curve representing dolomite.
fad From that point. follow the value horizontally to the left, and read the true porosity (<6) on the left-hand scale:
12%.

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