Page 310 - Petrophysics 2E

LAB-DERIVED EVALUATION OF SHALY 281

LOW CATION EXCHANGE CAPACITY
HIGH CATION EXCHANGE CAPACITY
FRESH
WATER WATER
Figure 4.47. Salinity and cation exchange capacity effect on formation resistiuitv
factor [31J

P a CLAY CONDUCTIVITY

SMTY FRESH
WATER WATER
Figure 4.48. Salinity and temperature effect on formation resistivity factor where
B = Ceq [31J.

and 45% relative humidity, leaving molecular layers of water on the
clay surfaces. This causes the measured porosity and grain density to be
lower than those measured for totally dried cores. Table 4.17 illustrates
the effects of using partially dried core porosity and grain density in
the Waxman and Smits equations. Column 1 shows the correct results
obtained by combining totally dried (180" -240°F) core porosity and
grain density with CEC to calculate Qv and water saturation. Columns
2 and 3 give the results of combining partially or humiditydried porosity
and grain density with electrical properties calculated on the basis of
oven-dried core porosity and humidity-dried core porosity, respectively.