Trondheim - 10.03.2016 1 - Bergmekanikk · Trondheim - 10.03.2016 25 Conclusions Analysis of...

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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