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268 PETROPHYSICS: RESERVOIR ROCK PROPERTIES
SALT SOLUTION L76m N
FRACTIONAL WATER SATURATION, Sw
Figure 4.41. Temperature dependence of I us. S, function.
Qv and n* are temperature independent. Figure 4.41 shows a typical
behavior of IR versus S, for various temperatures. This figure indicates
that a decrease in the resistivity index at the constant water saturation is
obtained with increasing temperature and, for temperatures greater than
80°C, the IR vs. Sw relationship is virtually independent of temperature.
Ideally, the laboratorydetermined electrical properties of cores would
be made at reservoir conditions of temperature and water salinity. Using
the Waxman and Thomas approach, however, laboratory properties can
be adjusted to reflect reservoir conditions, according to the following
equation:
(4.140)
where the subscript TL denotes the laboratory temperature and T is the
reservoir temperature. The effective clay-exchange cations, Qv, for the
