Page 96 - Basic Well Log Analysis for Geologist

POROSITY LOGS

Figure 31. Chart for correcting Compensated Neutron Log (CNL*) for lithology. Note: this is a Schlumberger chart; do not use
this chart with another type of neutron log (see text).
Courtesy, Schlumberger Well Services.
Copyright 1972, Schlumberger.
Given: The lithology is sandstone. Also, the apparent limestone porosity is 20%. The value for apparent limestone
porosity is read directly from a Compensated Neutron Log (CNL*). A Compensated Neutron Log (CNL*) ts not
shown here; instead the value is given to you.
Procedure:
|. Find the value for apparent limestone porosity (read from a CNL* log) along the scale at the bottom of the
chart. In this example, the value is 20%.
to Follow the value vertically until it intersects the diagonal curve representing lithology (in this case, sandstone).
3. From that point, follow the value horizontally to the left. and read the true porosity (5) on the left-hand scale.
Porosity = 24%.

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