Page 558 - Petrophysics

PETROPHYSICAL PROPERTIES 525

Combining Equations 8.41 and 8.44 gives:

s, = (”> spv (8.46)
1-4

Since l/wf >> l/hf, Equation 8.41 reduces to:

2 2
S, = -orwf = - (8.47)
Wf SVP

Substituting for wf , Equation 8.17 becomes,

(8.48)

Combining Equations 8.46 and 8.36 gives:
(P3 )
k=-( 1 (8.49)
3s& (1 - +)2

The derivation of Equations 8.33 through 8.49 assumes that the
fractures are rectangular, smooth, uniform, and that fracture length is
equal to the length of the rock sample. The constant 3 is specific to the
shape of the fracture. Equations 8.48 and 8.49 can be generalized for all
fracture shapes as follows:

(8.50)

(8.51)

where KTf = K&, Ksf being the fracture shape factor and T the tortuosity.
This equation is similar to the generalized Kozeny equation. Unlike
sandstone formations, identification and characterization of flow units
in carbonate formations is not possible because of extreme variations of
fissures, both in terms of geometry and intensity. However, in reservoirs
where the geometry and distribution of fissures are uniform throughout
the reservoir, one could use the same concepts of reservoir quality index
(RQI), flow zone index (FZI), and Tiab’s hydraulic unit characterization
factor (HT) as were presented in Chapter 3.