WellCAD Basics - Advanced Logic Technology

126 - BOOK 1 - WELLCAD BASICS
www.alt.lu
where:
ΦRHOB = porosity from density log (pu)
RHOma = matrix density (gr/ccm)
RHOB = log density (gr/ccm)
RHOf = density of pore fluid (gr/ccm)
RHOsh = shale density (gr/ccm)
Vsh = shale volume which is given through:
V sh
where:
� � �
�
� � � � 0.
33 2
�
�
GRlog
�GRmin
�
2�
�
�
�1
GRmax
�GRmin
�
�
�
�
�
GRlog = gamma ray log (observed values)
GRmax = maximum gamma ray reading (shale response)
GRmin = minimum gamma ray reading (clean formation)
The task is best completed in two steps. The shale volume is calculated first and
porosity is computed in a second step referring to the Vsh results.
Assuming that the Well Logs named GR and RHOB are contained in our Borehole
Document the following formula must me typed in to calculate the shale volume:
0.33 * 2^(2*( ({GR}-Min({GR}) / (Max({GR})-Min({GR})) ) ) -1)
The functions Min() and Max() as well as the reference to the GR log {GR} can
easily be inserted into the formula with a double click on the corresponding item in
the Logs respectively Functions list. Enter Vsh as name for the resulting Formula
Log into the Log Title box.