Geology Reference
In-Depth Information
3
a
I
Q
f
=
(7)
12
Equation (7) is referred as the cubic law which is valid for laminar flow
through parallel wall fractures with smooth surfaces. In natural conditions,
these assumptions usually do not hold good. The validity of cubic low is
discussed by several researches, viz. Lee and Farmer, 1993.
Under field conditions, it is usually difficult to determine the representative
distance between the fracture walls. At low applied stress, when the fractures
are open, the parallel plate approximation for fluid flow through fracture
may be valid. However, due to stress the contact area between fracture
surfaces will increase and, therefore, variation in fracture aperture should be
considered.
Flow Models
Depending on the porosities and permeabilities of the fractures and the
matrix blocks, the fractured rock formations can be classified into (a) purely
fractured medium, (b) double porosity medium, and (c) heterogeneous medium
(Fig. 2 ). In a purely fractured medium, the porosity and permeability is only
Figure 2.
Hydrogeological classification of fractured media (after Streltsova,
1975).
K
f
and
K
m
are the hydraulic conductivities of the fractures and the
matrix, respectively.
S
f
and
S
m
represent the fluid storativities of the fractures
and the matrix. A: purely fractured media. B: fractured formation. C: double
porosity medium. D: heterogeneous formation. In cases B, C, and D, the
fracture coating or “skin” may be hydrogeologically significant.
