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WG: Underground Construction & Mining
Mechanics of Engineered Fractures in Discontinuous Rock
Petersen 1999
E. Detournay, J.F. Labuz (UMN)R. Jeffrey, A. Bunger (CSIRO)A. Peirce (UBC), J. Napier (CSIR)and others
Hydraulic Natural fracture
Friday, October 2, 2009
Questions
• Engineering Questions• Improvement of caving process (pre-conditioning of rock mass)• Roof control• Improvement of connectivity of fracture systems• Density of engineered fractures• Detection and monitoring of fractures (passive and active wave
methods, tiltmeters)• Science Questions
• Large scale fracture toughness• Interaction between engineered fracture and pre-existing
discontinuity• Continuity and branching• Fracture geometry• Shear vs opening mechanism
Friday, October 2, 2009
Collaboration CSIRO-CSIR-UBC-UMN
• Laboratory Experiments• Fracture curving near free-surface• Fracture crossing of discontinuities• Experimental validation of tip asymptotics• Influence of stress jump• Fracture curving
• Field Experiments• Fracture geometry• Monitoring• Interaction with pre-existing discontinuities
• Theoretical Research• Scaling analysis• HF fracture numerical simulators• Influence of a free-surface• Parameters influencing fluid lag• Fracture recession
Friday, October 2, 2009
Laboratory Experiments (CSIRO)
• Experiments in glass and PMMA• Fracture curving (free surface)• Fluid lag• Tip asymptotics• Fracture geometry (stress jump)
• Experiments in rocks• Reorientation from an inclined wellbore• Fracture crossing discontinuities• Fracture curving
Friday, October 2, 2009
Experiments in Glass and PMMA with Photometric Full-Field Crack Opening Measurement
(Bunger, 2005)
Friday, October 2, 2009
Experimental Results
Linear Elastic Fracture Mechanics
Fluid/Solid Coupling in Tip Region
Garagash and Detournay, J. Appl. Mech., 2000,
2005.
Inner Asymptote Outer Asymptote
Friday, October 2, 2009
The Parameter Controlling Curvature of Shallow Hydraulic Fractures
Flatter saucers with larger values of:
Friday, October 2, 2009
Daylighting radius versus χ
Murdoch and Slack 2002, www.ces.clemson.edu/geology/murdoch
Watson and Laney 1906Watson 1910
Friday, October 2, 2009
Stress Jump Control of Hydraulic Fracture Height Growth
SCL3_4 SCL3_9
SCL3_18 SCL3_26
Time=34 sec Time=67 sec
Time=273 sec Time=798 sec
Her
niat
ion
into
low
stre
ss z
one
Enhanced Images
Con
fined
by
high
stre
ss z
ones
High
Med
Low
High
High
Low
Profile machined according to elasticity solution
Stress jump results from pressing together
P
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
t1
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
t1t2<
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
t1t2<t3<
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
t1t2<t3<t4<
Friday, October 2, 2009
Reflectivity imaging
• Tracking crack tip location• Goal: Obtain image of growing fracture footprint and crack opening
Sample no. (time)
t1t5< t2<t3<t4<
Friday, October 2, 2009
Fracture crossing experiments
Top plate
Injection Line
Pump
Friday, October 2, 2009
Block that has been tested
Friday, October 2, 2009
Fracture Crossing
Renshaw and Pollard (1995)
Predict crossing if: HF
NF
Experiments: Ella Maria Llanos, PhD Thesis, 2009
Predicted arrest
Predicted crossing
Friday, October 2, 2009
Reorientation from an Inclined Wellbore
• Classical fracture mechanics problem in 2D
• Not well understood in 3D, with role of wellbore, and in heterogeneous material
• Study through serial sectioning crack surface reconstruction
Friday, October 2, 2009
Numerical Modeling
• 2D Simulations with tracking of both fluid front and crack edge
• Planar 3D Simulator
• Non-planar 3D Simulator
• Interaction between HF Fracture and discontinuities
10−15 10−10 10−5 1000
0.2
0.4
0.6
0.8
1
!R
" f
10−15 10−10 10−5 10010−1
100
!R
IFGARIMMAasymptotic
#
#f
Figure 5: Evolution of the fracture front, the fluid front and the fluid fraction for an axisymmetric
fracture, for K = 0.485 and S = 0. The fracture front and the fluid front are shown in toughness
scaling. The time scaling used in RIMMA is adopted in the plots.
10−15 10−14 10−13 10−12 10−11 10−10 10−910−6
10−5
10−4
10−3
10−2
10−1
100
!R
# R, "
f
RIMMAIFGAasymptotic
"f
#R
Figure 6: Transition from the O-asymptote to the O-asymptote for an axisymmetric fracture, for
K = 0.056 and S = 0. The time scaling used in RIMMA is adopted in the plots.
34
(UMN, CSIRO)
(UBC, UMN)
(CSIR)
(CSIRO, UMN)
Friday, October 2, 2009
Planar 3D Hydraulic Fracture Simulator
The signed distance function
Friday, October 2, 2009
DD HF model of fracture with offsets
1. Large pressure gradientat offset sites.2. Large fracture openingbehind (upstream of) these points3. Slower overall fracture growth.
Friday, October 2, 2009
CSIRO.
The New 3D Fracture Simulator Gives Promising Match to Experimental Observations For:
• Breaking of initial symmetry, i.e. movement of the crack centre
• Shallow fracture crack path and fine scale features such as river line surface roughness
• Formation of petals near initially inclined hydraulic fractures
Experiment
Simulation
Friday, October 2, 2009
Former Field Experiments (CSIRO)
Friday, October 2, 2009
Fracturing equipment at underground site atRidgeway Gold Mine, NSW.
Surface site at MooneeFriday, October 2, 2009
Preconditioning
• Characterize rock mass• Instrument site• Place 4-8 HFs • Post-frac rock mass
measurements• Map & sample fractures (mine-
through)• Evaluate model predictions
against data
Jeffrey 2001, CSIRO
4850 level
E26
E48
Surface RL 10280m
Undercut level RL 9700m Previous Mine through site
Friday, October 2, 2009
Green plastic proppant in hydraulic fracture placed during E48 consortium project
Friday, October 2, 2009
Fracture 8, south side of tunnel at 38.5m chainage
Tilt vectors for E48 fracture indicating sub-horizontalorientation.
Friday, October 2, 2009
Any other comments?Fractures mapped in E48 tunnel – three views shown. Large offsets are indicated by numbers.
Friday, October 2, 2009
Engineered fracture
Preconditioning:
Jeffrey 2006
The experiments will consist of several stages:1. Analyses and designs of fracture treatment2. Characterization of local site conditions3. Installation of monitoring instrumentation 4. Mobilization of fracturing equipment and materials5. Fracturing and measurement of response6. Post - fracture characterization7. Mine through and mapping 8. Analytical and numerical modeling9. Supporting laboratory experiments
Friday, October 2, 2009
Preconditioning
Engineered fractures in discontinuous rock • Crack initiation• Scaling• Crack interactions• Interface fracture• Shear v opening mechanisms• Coupled processes• Microseismics & imaging
Friday, October 2, 2009
Mine-through
Combine with cutting researchFracture geometry, width & extentContinuity & branchingInteraction w/ existing fractures
Friday, October 2, 2009