Page 550 - Petrophysics
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PETROPHYSICAL PROPERTIES 517
The general form of this equation is:
(8.25b)
For a single porosity system, this equation reduces to:
(8.26)
The constant 2 in Equation 8.26 is related to the shape of the capillaries
and their tortuosity and can be replaced by KT:
(8.27)
where
KT = 6fsp~ (8.28)
Methods for estimating the pore shape factor fsp and the tortuosity of
the capillaries z are discussed in Chapter 3. In the case of formations
containing a very small number of channels per unit pore volume, such
as in reservoirs with high storage capacity in a rock matrix, and very low
storage capacity in channels, nl >> n2, Equation 8.25a can be written as:
where the subscript 1 stands for primary pore space, which stores most
of the fluid. In the case of n2 >> nl , i.e. rocks in which the fluid is stored
mainly in secondary pore spaces such as fissures and vugs, Equation 8.29a
becomes:
where the subscript 2 stands for secondary pore space. Thus, in
cases where nl >> n2 and n2 >> nl, double porosity systems may be
