Transcript Slides

Hydromechanical modeling of
fractured crystalline reservoirs
hydraulically stimulated
S. Gentier*, X. Rachez**, A. Blaisonneau*,
*BRGM
** Itasca Consultants->BRGM
BRGM/Geo-Energy unit
February 13-15, 2006
In situ hydraulic stimulation tests at Soultzsous-Forêts
Irreversible increase of the
permeability around the wells but
not in the same proportions for the
all the wells
Gérard et al., 1997
13
12
(2)
11
(1)
10
9
Pdh-Po (MPa)
>
8
7
(1) Stim. GPK1 -1993
Legende
(3)
6
GPK1 Stim ulation 1993 (Estimat ion)
GPK2 Stim ulation 95JUN16
GP K2 St im ulation 96SEP18
5
(2) Stim. GPK2 -1995
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GPK2 Test s injec tion 96SE P29
GPK2 Tests injection 95JUL01
GPK1 Test s injec tion (94July )
(4)
3
(3) Injec. GPK2 -1996
GPK2 Tes t injection après reparation 95AUG15
GPK1 Injection 96OCT13
GPK2 Production 96OCT13
2
(4) Injec. GPK1 -1994
1
Tran-Viet/BGR 10/96
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
Qin (l/s)
Stimulation curves (GPK1/GPK2)
>
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February 13-15, 2006
Gérard et al., 2004
Micro-seismic events
associated to the hydraulic
stimulation tests
Micro-seismic events (GPK2/GPK3)
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Objectives of our modeling work
and of the talk...
> Objective of our work
•
•
•
at BRGM is:
to understand which physical mechanisms are
involved in the hydraulic stimulation of the well in
crystalline rocks
to extract the main parameters playing a role in the
hydraulic stimulation
to establish the link with the micro-seismic activity
observed during the hydraulic stimulation tests
> Objective of my talk is much less
ambitious :
•
to give you an idea of the first results obtained up to
now by means of some examples extracted from the
various hydraulic stimulation tests performed at
Soultz-sous-Forêts
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Hydro-mechanical modeling approach
>> Conceptual
Numerical tool
model
: 3DEC
:
code
• The rock massa isreal
considered
integrating
HM as
a blocks assembly
coupling
based which
on : are
>
6
separated by discontinuities
Distinct Element method for the
•• Blocks
are deformable and
mechanical part
impermeable
Finite difference schema for
•• Flow
takes place in the
the hydraulic part of the model
fractures exclusively
the discontinuities
• inThermal
effect is neglected in
a first step for two reasons :
consider the
very short
duration
Aim : –
to we
simulate
interaction
betweentest
mechanical process
– we are interested in what it
(deformations,
stresses,…)
and
could happen
at some distance
of process
the well (the(pressures,
Thermo-Hydrohydraulic
Mechanical behavior of the near
apertures,…)
well is in progress with another
and more appropriated
numerical tool)
3
F
2
1000m
1
7
5
400m
400m
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February 13-15, 2006
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What kind of data do have we to construct
the model ?
well
> hydraulic stimulation tests :
solicitation in the well
Injection under
P = Pi + D P
> Stress regime (?): mechanical
boundary conditions
•
•
Klee and Rummel (1993)
Cornet et al. (to be published)
> Fracture network mobilized
during the hydraulic stimulation :
•
North
x=z=0
East
x=z=
0
Pi = r g z
identification of this network from :
– flow logs
– temperature logs
– geological analysis (cutting analysis)
– bore-hole imagery
y=0
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February 13-15, 2006
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What it could happen during the hydraulic
stimulation of a well (if we exclude thermal effect...)
H
V
V
h
H
h
But in general, the granite is
already fractured
In continuous homogeneous and
isotropic medium
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February 13-15, 2006
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More in details...
Evolution of the hydraulic aperture is
linked to the normal displacement (Un)
and the tangential displacement (Us)
opening : reduction of the normal component
T1
Un
Us
release of the shearing
T2
Tf
Un
H
Increase of the aperture
Well initial state
To
V
Us
H
h
closure of the fracture
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February 13-15, 2006
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Four examples...
To illustrate our Hydro-Mechanical
modeling approach, we are going to
consider the influence of the following
parameters :
>
>
>
>
number of fractures involved in the stimulated
network (GPK1)
orientation and dip for a given fracture network
(GPK2)
heterogeneity of the hydro-mechanical
properties of fractures (GPK3)
stress regime (GPK4)
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February 13-15, 2006
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Influence of the number of fractures (GPK1)
#8
#1?
#1
F
5 1 64
3
#1
most
permeable
in situ
2
6
1
1
4
3
3
2
Model
withwith
8 fractures
2
GPK1
- Model
8 fractures
real injection test
total flowrate at well
flowrate in fracture #1
flowrate in fracture #2
7 #3
flowrate in fracture
7 #4
flowrate in fracture
flowrate in fracture #5
3
flowrate in fracture #6
5
flowrate
in fracture #7
flowrate in fracture #8
5
2
0
10
4
20
Flowrate [l.s-1]
30
40
Overpressure applied in well [MPa]
Overpressure applied in the well [MPa]
6
:8 the
# 4, 5, 6
10
10
8
Model with 7 fractures
GPK1 - Model with 7 fractures
real injection test
total flowrate at well
flowrate in fracture #1
flowrate in fracture #2
flowrate in fracture #3
flowrate in fracture #4
flowrate in fracture #5
flowrate in fracture #6
flowrate in fracture #7
6
4
2
0
10
20
Flowrate [l.s-1]
30
40
No
change2884
in the
global
but
Extrasignificant
fracture (depth
m, dip
80°,behavior
dip-dir 230°)
significant
change
ininthe
#1
: better
with
Hydraulic
apertures
thefracture
fracture
zones
connecting
two fractures
in
the upper
part offitting
the open
the
holein situ flow log data
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February 13-15, 2006
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Influence of the number of fractures (GPK1)
View in plane of Fracture #1
Model with 7 fractures
- Overpressure DP=10.0 MPa
Model with 8 fractures
Extra fracture
GPK1
Maximum Aperture # 0.20mm
Few meters from well
GPK1
Maximum Aperture = amax = 0.25mm
Connection with other fractures
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February 13-15, 2006
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Influence of the geometry (GPK2)
Regular
network
N 250° ->
N 290°
Us
Usmax
max2.5
5 cm
cm
Shearing
concentrated
thetop
lower
Shearing is
propagates
frominthe
to the
part
of the
open
hole
bottom
of the
open
hole
Tangential displacements
DP = 14 MPa
Statistical network
Us max  6 cm
Shearing is concentrated in the
upper part of the open hole
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February 13-15, 2006
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Heterogeneity of the hydro-mechanical properties
(GPK3)
Dezayes et al. (2004)
4750m
4860m
4905m
4930m
4960m
4980m
5015m
4% of
75%
offluid
fluidflow
flow
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February 13-15, 2006
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Influence of the heterogeneity in the hydromechanical properties (GPK3)
100
90
% Flowrate (25 l/s)
80
in situ
Hyp. 1
Hyp. 3
70
60
50
40
30
20
10
0
-4400
-4500
-4600
-4700
-4800
-4900
-5000
-5100
Depth (m)
DP = 10.5 MPa
Overpressure (MPa)
F0
F1
F2
F3
F4
F5
F6
F7
Well (model)
Well (in situ)
Flow rate (l/s)
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February 13-15, 2006
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Heterogeneity of the hydro-mechanical properties (GPK3)
Existence of a very
permeable fracture
Slip : points of
rupture

Micro-seismicity ?
limited extension of
shear displacements
for this range of
overpressures
Increase of the
permeability
remains
moderated
E
W
Us max  1 cm
Shear displacements
2D/cross section (EW)
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February 13-15, 2006
DP = 15 MPa
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Stress regime ?
Stress (MPa)
50
100
0
150
0
Sh(1)
SH(1)
500
Depth (m)
1000
SV(1)
Phyd
V
SV(2)
1. Klee and Rummel (1993)
H : N170°
2. Cornet et al. (2006?)
H : N 175°
SH(2)
1500
Sh(2)
Shmin(2)
2000
Shmax(2)
Normal fault
stress regime
2500
?
3000
3500
4000
H
4500
5000
Phyd
h
Strike slip regime
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February 13-15, 2006
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Influence of the stress regime
DP = 18,3 MPa
(GPK4)
Tangential
Normal fault stress
Tangential
displacements
more concentrated
in some fractures
displacements
more spread
regime
Strike slip regime
Us max  6 cm
Us max  12 cm
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February 13-15, 2006
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Conclusions
>Increase of the permeability could be explained by :
•
shear mechanisms which are developed only in some fracture zones
depending of :
– geometry and connectivity of the fracture network / stress field
– heterogeneity in the hydro-mechanical properties of the fracture in the
network
This modeling approach can help to understand better a geothermal site but
it must be based on a good geological and structural knowledge of the site
>Difficulties in relationship with the site :
•
•
•
definition of the in situ stress regime
definition of the fracture network. The model is very sensitive and requires
good structural data
how this main stimulated fracture network is connected to the global
fracture network constituting the real volume of the exchanger?
>Difficulties in relationship with the model :
•
which law of behavior to consider for the main fracture zone and how to
define the associated hydro-mechanical parameters ?
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February 13-15, 2006
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