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Hydrofrac-Test Demonstration
1969 granite quarry N-Minnesota
private photo F. Rummel
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… more than 25 years of experience in hydrofrac testing all over the world !
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0
1
2
3
4
5
6
7
8
9
depth
[km
]
0 100 200 300principal stresses [MPa]
Sh
SH
Sv
1500
2000
2500
3000
3500
Depth
[m
]
10 20 30 40 50 60 70 80 90 100Stresses [MPa]
Sv
Sh
SH
96SEP1895JUN16
Highlights…
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Deep Hydraulic Fracturing Stress Measurements
- Case Study from a Geothermal Energy Project in Australia -
A. Larking, G. Meyer GreenRock Energy, West Perth, Australia
A.P. Bunger, B. Shen, R. Jeffrey CSIRO, Melbourne, Australia
G. Klee, F. Rummel MeSy-Solexperts GmbH
Klee G, Bunger AP, Meyer G, Rummel F and Shen B. 2011. In-situ stress in borehole Blanche-1/South Australia derived from breakouts, core discing and hydraulic-fracturing to 2 km depth. Rock Mechanics and Rock Engineering, 44:531-540
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Australia is the world sixth – largest country.
Population of 21 million people.
Large mineral resources, including coal, oil and natural gas.
Electricity generation is dominated by coal-fired plants.
GHG emission intensity is one of the highest in the world.
In 1997, Australian government announced a series of measures
designed to reduce the emissions of GHG.
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Australia - Geothermal Energy Potential
S-Australia
heat flow density
of 90 W/m2
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Principle of Hot-Dry-Rock (HDR, HFR, EGS)
In – Situ Stress Regime controls…
pressure to induce fractures or to
stimulate pre-existing joint systems
flow resistance
direction of the underground fluid
flow path
micro-seismicity
borehole stability
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Olympic Dam Geothermal Project
Borehole Blanche-1 drilled near the western edge of the Roxby Down Granite (part of the Burgoyne Batholithe)
depth: 1934.6 m, open-hole diameter: 76 mm below 830.1 m
bottom-hole temperature: 86 °C
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Regional Stress Data
www.world-stress-map.org, 2008
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Analysis of Borehole Breakouts
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Analysis of Borehole Breakouts with FRACOD2D (Fracon Ltd., Finnland)
for 3 cross-sections at 1146.5 m, 1247.5 m and 1392.5 m the breakout dimensions were modeled
55.5
0.25a
a=37.7mm71.1
0.25a
breakout geometry at 1392.5 m
-0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
X Axis (m)
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Y A
xis
(m
)
-0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
X Axis (m)
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Y A
xis
(m
)
Green Rock Energy _ Borehole breakout (1392.5m)
Pxx (Pa): -8.75E+7 Pyy (Pa): -4.145E+7
Pxy (Pa): 0E+0
Max. Compres. Stress (Pa): 4.53139E+8
Max. Tensile Stress (Pa): 6.90692E+7
Elastic fracture
Open fracture
Slipping fracture
Fracture with Water
Compressive stress
Tensile stress
Fracom Ltd
Date: 19/05/2007 09:38:09
numerical modeling result
SH / Sh / Sv (2.5-2.75) / (1.25-1.5) / 1
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Analysis of Core Discing
discs are flat, slightly upwardly cup-shaped or saddle-shaped
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Core Disc Characteristics – Saddle Shapes
after Matsuki et al. (2004), IJRMMS
sections of core oriented using natural fractures that appear in the
BHTV-log
maximum curvature of saddle shapes oriented at N (185-187),
the minimum horizontal stress direction implied by breakouts
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Disc Length Distributions
8 zones of 40-70 m length
tending to cluster with similar length discs
right tail dominated disc length distributions in shallow sections
bell-shaped distributions in the deepest sections
0 1000 2000 3000 4000 50000
2
4
6
Scale (mm)
Down Hole
Depth=1029-1079m
0 5 10 15 20 25 30 350
5
10
15
20
L/R
N(L
/R)
0 500 1000 1500 20000
2
4
6
Scale (mm)
Down Hole
Depth=1887-1926m
0 1 2 3 4 5 6 70
100
200
300
400
L/R
N(L
/R)
Shallow – Right-Tail Dominant Deep – Bell Shaped
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Stochastic Discing Analysis (for details see Bunger AP, 2010, RMRE, 43(3):275-286)
• Assumes randomly varying in situ stresses and rock strength follow normal distributions.
• Discing occurs when the local stresses and rock strength conditions satisfy a failure criteria (Matsuki et al. (2004), IJRMMS)
• Monte Carlo technique used to predict disc length distributions for given in situ conditions
• Choose parameters of stress and strength distributions so that predicted disc length distributions matches measurements
2
2
std~ , ( )
s, )d~ t (
x x
y y
N
N
2
2
~ , ( )std
)s~ , td(
z z
t t t
N
N
0( ) ( ) ( )s s sx x y y z z t
L L Lk k k
R R R
Rock Tensile
StrengthIn situ stresses
Numerically determined,
length dependent functions
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Analysis of Core Discing – In-situ Stress Estimates
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
depth
[m
]10 20 30 40 50 60 70 80 90 100 110
Sv, Sh and SH [MPa]
Sh
SH
Sv (2.65 g/ccm)
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Hydraulic-Fracturing Tests using the Wireline Approach
disadvantage
limited pull-out force
advantages
no drill-rig/crew necessary
downhole pressure monitoring
high system stiffness dP/dV
fast (impression packer testing)
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Hydraulic-Fracturing Tests using the Wireline Approach
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Hydrofrac Test Record
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Pre- and Post-Frac BHTV-logs
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
depth
[m
]
10 15 20 25 30 35 40 45 50 55 60Pc, Pr and Psi [MPa]
Pc
Pr
Psi
Sv (2.65 g/ccm)
Characteristic Pressure Values
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Hydrofrac Stress Calculation
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project site
Blanche-1: Orientation of Maximum Horizontal Stress
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Blanche-1: Comparison of Stress Magnitudes
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
depth
[m
]
10 20 30 40 50 60 70 80 90 100 110Sv, Sh and SH [MPa]
Sh (HF)
SH (HF)
Sh (core discing)
SH (core discing)
Sh (breakout)
Sh (breakout)
Sv (2.65 g/ccm)
Result of Hydrofrac Tests
Sh = (12.4±1.2) + (0.038±0.003) · (z - 880)
SH = (35.8±2.8) + (0.060±0.010) · (z - 880)
Sv = 0.026 · z
SH = N 97° 3°
(z in m, Sv, SH, Sh in MPa)
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Conclusions
Analysis of breakouts, core-discing and hydraulic-fracturing tests yield consistently an
E-W orientation of the maximum horizontal stress SH.
The results of the different methods indicate that the vertical stress Sv is the minimum
principle stress, at least at the bottom of the investigated borehole section.
High horizontal stresses will favor the creation of horizontal fractures during
stimulation of the geothermal reservoir and will require operation pressure in the
order of the vertical stress.
High horizontal stresses were reported for the coal mines throughout the Eastern
Coal Basin of New South Wales as well as for the Cooper Basin.
Concluding Remark
Combination HF with HTPF
Stress profiles rather than singular measurements
Cost efficiency by using a wireline system