Page 137 - Petrophysics 2E

1 10 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

(b) The specific surface area per unit pore volume is given by
Equation 3.1 5 :

2
svp = -
r
2
svp = = 4,237 cm-'
4.72 x 10-4

The specific surface area per unit grain volume can be estimated using
Equation 3.17:

All the above equations used in deriving the relationship between the
permeability and porosity (Equation 3.19) are based on the assumption
that the porous rock can be represented by a bundle of straight capillary
tubes. However, the average path length that a fluid particle must travel
is actually greater than the length L of the core sample. The departure of
a porous medium from being made up by a bundle of straight capillary
tubes can be measured by the tortuosity coefficient, 2, which is expressed
as [16,17]:

2= (;) 2 (3.20)

where La is the actual flow path and L is the core length. Note that in
the literature tortuosity is sometimes defined as LJL. Equation 3.20 is
preferred here because in most laboratory experiments, the product of
the formation resistivity factor (F) and porosity is related to the ratio LJL
by the following correlation [ 171 :
F@= (+)' (3.21)

The exponent C is the correlation constant, which ranges from 1.7 to 2.
Note that this range is rather similar to that of the cementation factor m.