Geology Reference
In-Depth Information
fractures and act as uniformly distributed source. Such an approach with
some modifications has been also used by several researchers in analyzing
the behaviour of fractured oil reservoir (Anon, 1996).
Figure 3.
Types of double porosity aquifers: (a) Horizontal fractures and
matrix blocks; (b) Spherical matrix blocks, and (c) Cubical matrix blocks.
In the double-porosity model, the porous blocks have high primary porosity
but low hydraulic conductivity while the adjacent fractures have although
low storativity but high conductivity. The difference in pressure between the
porous blocks and the fractures lead to flow of fluid from porous to adjacent
fractures. Due to difference in the permeabilities of fracture and blocks, flow
mechanism is different during early, long and intermediate times of pumping.
The characteristics of a double (dual) porosity aquifer system are given
in terms of
K
f
,
K
m
,
S
f
, and
S
m
, where subscripts f and m are for fractures and
matrix respectively. The other two parameters are storativity ratio () and
the transmissivity ratio (
) is the ratio of fissure to total
system (blocks plus fissures) storativities and can be expressed as
). Storativity ratio (
S
SS
f
=
(8)
f
m
where
S
f
and
S
m
are the storativities of fractures and blocks respectively, and
is a factor depending on matrix block geometry which is taken to be equal
to l for strata type. The transmissivity ratio, or interporosity flow coefficient
(
) (dimensionless) is given by:
K
2
m
ar
=
(9)
w
K
f
