Geology Reference
In-Depth Information
Kt
Sr
4
KK rs
Q
K
H
rK
where
z
f
is the distance between the fracture and the bottom of the aquifer,
and
H
the aquifer thickness.
K
r
, the permeability along the radial direction
parallel to the fracture, can be interpreted as the permeability increased by
the existence of the horizontal fracture.
K
z
, the vertical permeability,
represents the matrix permeability,
S
s
the specific storage coefficient,
t
the
time since the pumping started,
r
f
the radius of the horizontal fracture,
s
the
drawdown and
Q
the pumping discharge rate.
Adjustment of observed drawdowns by Gringarten theoretical curves
(Fig. 3) leads to high value of
H
DG
, suggesting a high permeability anisotropy.
Difference between observations and theoretical curve at short times is
attributed to well losses in the pumping well. Knowing the geometry of the
case (i.e. the thickness
H
of the aquifer), supposing the distance
z
f
between
the bottom of the aquifer and the fracture equal to half
H
and using the
value determined by Maréchal et al. (2005) using Neuman method for
S
s
(9.7 × 10
-5
at IFP-9), the hydrodynamic properties of the aquifer are evaluated
(Table 2):
K
r
the horizontal permeability,
K
z
the vertical permeability and
the radius
r
f
of the horizontal fracture. It is observed that the anisotropy of
the aquifer is shown in the pumping wells while estimated fracture radius
is coherent with field observations.
r
rzf
r
t
DG
=
,
s
DG
=
and,
H
DG
=
2
sf
f
z
Table 2:
Permeability, anisotropy degree and radius of the horizontal fracture
determined at pumping wells using Gringarten method
Known parameters
Parameters determined by adjustment
z
H
K
K
Pumping
H
Fissure
z
f
S
s
*
H
DG
r
f
K
r
K
z
f
r
()
()
Well
(m)
(m)
(1/m)
(-)
(m)
(m/s)
(m/s)
z
IFP-9
7.3
F9/1
4.0
0.55
9.7E-05
5
3.4
2.9E-05
5.2E-06
5.5
*
S
s
is the average of specific storage coefficient determined for each site using
Neuman method at observation wells.
10
Observations
Gringarten model
H
DG
= 5
1
10
100
1000
Time (min)
Figure 3.
Adjustment of drawdown in pumping well IFP-9 using
Gringarten theoretical curves.
