AIPG Marcellus Shale Hydraulic Fracturing Conference
Discrete Fracture Network Models of
Natural and Hydraulic Fractures
William Dershowitz and Thomas Doe
Golder Associates
Redmond, WA
Talk Overview




Discrete
Di
t F
Fracture
t
Network
N t
k Models
M d l
Stimulation of Natural Fractures by
Hydraulic Fractures
Microseismics and Critical Stress
B ildi and
Building
dA
Applying
l i aH
Hydrofracture
d f t
DFN Model
Discrete Fracture Generation

Stochastic Inputs & Deterministic Features
O i t ti
Orientation
Si e
Size
Intensity
kh
Defining the Fracture Permeability & Aperture

Storage aperture can be defined from
image logs and conventional logs;
 Hydraulic aperture needs to be defined
with respect to well tests and interference
observations;
 Permeability defined from:

Well test analysis;
 Analysis
A l i off mud
d lloss d
data;
t
 Dynamic simulation.

The stochastic nature of the DFN
approach
h means th
thatt the
th uncertainty
t i t off
these properties can be addressed.
Fracture Set 1
kh
Fracture Set 2
kh
Principal Stress & Hydraulic Fractures
Arrows show direction
of maximum and
minimum principal
stress.
Hydraulic fractures are
represented in model
as pink fractures.
This model is then
combined with the
natural fractures.
fractures
hmin
hmax
Mohr Circle Description of Stress
Effective Stress and Pore Pressure
Fracture Types





Hydraulic
H
d li F
Fracture
t
 Created by fracturing process
Inflated Natural Fractures
Rough, Shear-Dilated Fractures
Smooth, Non-Dilated Fractures
Unaffected Fractures
Micro-Seismicity
Inflated Fractures
max
Hydraulic Fracture
max
Inflated Natural
Fractures
Account for Most Fluid
Roughness and Permeability
Rough Fracture
Smooth Fracture
roughness
angle, 
Significant T Increase
Minor T Increase or Decrease
Natural Fracture Stimulation
Natural Fracture Stimulation
Simulation of Hydraulic Fracture by FracMan

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
Create Natural Fracture
Network
Superpose grid with stress
and rock property data
Grow Hydrofracture
 Sneddon elastic crack
solution
 Balance Injection and
Hydrofrac Volumes
Modify Connected Natural
Fractures According to
Type
Visualize Microseismicity on
Critically Stressed Fractures
Induced Hydraulic Fracture
Propped Natural Fractures
Non-Inflated Critically-Stressed
Natural Fractures
DFN example
Building
g the well scale DFN model up
p
from well data and geological
understanding
10
1
N o rm aliz ed N u m b er
Fracture size data
from seismic, well
and outcrop data
0.1
0.01
0.001
0.0001
1
10
100
1000
10000
Trace Length (meters)
Orientation data
from Image logs
Intensity data from
Image
age logs
ogs
Area 2.8mi x 2.1mi
Frac Stage 1
Hydraulic fracture &
inflated natural fractures
Shown without DFN
Material Balance Includes Hydrofrac and Inflated
Fractures
Controls meshing size of fractures for
volume and critical stress calculations
Controls pressure decay
away from wellbore
Controls updating of the
fracture apertures and
resultant transmissivity
Determines the perm.
improvement for the
fractures
Frac Stage 1
Hydraulic fracture &
critically stressed
natural fractures
(inflated & non-inflated)
Shown without
natural fractures
Frac Stages 1-3
Hydraulic fracture system
Stage 2
Stage 1
(Hydraulic fracture plus inflated natural
f t
fracture)
)
Stage 3
Stage
g 2
Hydraulic fracture
without inflated
natural fractures
St
Stage
1
Frac Stages 1-3
Stage 2
Stage 1
Hydraulic fracture system
(Hydraulic fracture plus critically
stressed
t
d fractures
f t
- inflated
i fl t d and
d
noninflated)
Stage 3
Stage
g 2
Shown without inflated
natural fractures
Stage
g 1
Modeling Microseismicity
Modeled Microseismic
Measured Microseismic
Modeled and Measured
Microseismic
Modeled Microseismic
with hydraulic fracture
Application



Calibrate model to
microseismic responses
Superpose “convex hull” to
determine tributary drainage
area
Apply to predict fracture
interactions in reservoir
where there are no
microseismic
i
i i data
d t