Page 271 - Petrophysics 2E
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244 PETROPHYSICS: RESERVOIR ROCK PROPERTIES
formation can be expressed as [21]:
(4.66)
where Vsh is the laminar shale volume estimated from:
hshi and ht are defined in Figure 4.29. Rsd is the resistivity of the
clean sand layers:
(4.68)
where Fsd is the formation resistivity factor of the sand beds. Using
Equation 4.35, F,d is equal to:
(4.69)
where @sd is the sand-streak porosity:
(4.70)
and @ is the bulk-formation porosity. Thus, the general expression
for the formation resistivity factor for sands laminated with thin
shale streaks is:
(4.71)
Combining equations 4.66-4.71 and solving explicitly for the water
saturation &, one obtains:
(4.72)
In practice, laminar shales are considered to have the same average
properties (such as Rsh) as the closest thick shale body, because,
in all probability, they have been subjected to the same geological
process of deposition. The porous sand beds also are assumed to have
the same effective porosities, permeability, and water saturation.
Equation 4.72 can be simplified by assuming that the cementing