Page 562 - Petrophysics

PETROPHYSICAL PROPERTIES 529

(b) Hydraulic radius can be calculated using Equation 8.58b.

2 114
rM = (- (314) (0.015)') = 0.12 cm
3n:
This value of rhf implies that a fracture which has a height of 314 cm
and a width of 0.015 cm, is equivalent to a cylindrical channel which
has a hydraulic radius of 0.12 cm.

TYPE 2 NATURALLY FRACTURED RESERVOIRS

In this type of reservoir the matrix has a good porosity and
permeability. Oil is trapped in both the matrix and fractures. Consider
a representative block containing two parallel layers, as shown in
Figure 8.2 1.
The average permeability in the matrix can be modeled using the
capillary tube model and equations developed in Chapter 3. The average
permeability in the fracture system can be expressed by the equations
developed in previous sections in this chapter.
For n, capillaries and nf fractures, the following approach can be
followed to estimate permeability in type 2 naturally fractured reservoirs.
Total flow rate from both matrix and fractures can be expressed as:

Fracture
hr

Figure 8.21. Representative elementary rock volume containing two parallel systems
of matrix and fracture. The Puid is stored in both matrix and fractures (type 2
reservoirs).