Sustaining Fracture Area and Conductivity of Gas
Shale Reservoirs for Enhancing Long-Term
Production and Recovery
08122-48
Hugo Morales
Terra Tek
RPSEA Unconventional Gas Conference 2012: Geology, the Environment, Hydraulic Fracturing
April 17-18, 2012
Canonsburg, PA
rpsea.org
Loss in
fracture
conductivity
Project Goals
Loss in
fracture
area
Sh l Pl
Shale
Plays: B
Barnett,
tt H
Haynesville,
ill and
dM
Marcellus
ll
2
Objective
Propped
Un‐Propped
Evaluate
fracture
conductivity
d i i off
propped and
un-propped
fractures
Presentation Outline
Testing procedure
Tests with no proppant - roughness effects
Tests with proppant
 Constant
stress tests - Creep test
 Proppant
mesh sizes
 Rock/fluid
interaction
Impact of fracture conductivity on production
Conclusions
Step by Step Testing Procedure
 Cut horizontal cylindrical samples (1-1/2 in. by
3 to 4 in. ) with bedding
g planes
p
p
parallel to the
cylinder axis.
 Measure the UCS and BHN
 Split samples into two or three cylindrical subsections
 Fracture sample by Brazil loading, wedge
cutting, or saw cutting
 Position
P i i sample
l iinside
id a rubber
bb sleeve
l
and
d
inside the assembly vessel filled with confining
fluid.
 Inject DI water 0
0.1
1 cc/min (confined chamber at
testing pressure and temperature)
 Measure fracture conductivity by equivalent
Darcy’ss flow.
Darcy
Fracture Closure Measurement
Measure changes in
fracture width during
testing
Differentiate between
embedment and
deformation
Testing Matrix
Best
G d
Good
Barnett
Poor
Fair
stress 5000 psi
 Fluid rock interaction
Good
Fair
Haynesville
Poor
Best
Good
Tests
T t with
ith outt proppantt
 Creep tests (Constant
tests
Mixing proppant sizes
Marcellus
T t without
Tests
ith t proppantt
Fracture Conductivity Tests with no Proppant
Saw Cut
Brazil
Natural
Asperity or
Wedge Cut
Saw Cut
S
C t
Smooth
Brazil
B
il
Rough
Nat.
N
t Asp.
A
Rougher
Roughness of Shale Samples
Hp
Hv
H H
P
n P  nV
f  nP  nV
L
Sample
Saw Cut
Saw Cut
Brazil
Natural Asperities
Asperities R
Roughness 9 72 m
9.72 m
313.3 m
563.8 m
Frequency
12
18
10
V
Fracture conductivity vs. roughness at 1000 psi
and 4000 psi confining stresses
Saw Cut
Brazil
Barnett – Good quality reservoir
Nat. Asp
Roughness and Conductivity of Shale Fracture Face
18”
S
Sample
l Roughness R
h
12”
1
2
3
4
5
6
260 m
290 m
290 m
249 m
435 m
491 m
491 m
690 m
C
Creep
T
Tests:
t 5000 psii constant
t t stress
t
Creep Loading: Constant Stress 5000 psi
100 Mesh Proppant
Enhanced Creep Pictures of Proppant
Tap Water
N2
Barnett: Best RQS
Q
Creep Response - Average for three Plays (32 Tests)
Mi i P
Mixing
Proppantt Si
Sizes
Mixing
g Proppant
pp
Sizes
40/70
220 to 410 m
Mix
100
100 m
Obj ti
Objective:
Improve long term conductivity by controlling
g the larger
g proppants particles
embedment; allowing
offset embedment of smaller particles.
Proppant Embedment –
Marcellus Good QRS
100
M h
100 Mesh 100 Mesh
Mix Mix
40/70 Mesh
40/70 Mesh Mixing Proppant Sizes – Barnett
Mixing
Sizes – Marcellus
g Proppant
pp
Mixing Proppant Sizes – Average Conductivity (24 Tests)
Summary Plot – Including Nat. Asp. (No Proppant)
Fluid/Rock Interaction Tests
Tension
Objectives


Measure the effect of injecting a
water base fluid into reservoir (DI
water soaked sample), and
Measure the effect injecting an oil
base fluid into the reservoir (oil
soaked sample)
p )
Brazil Fracture
Water Solution
DI Water
Oil Solution
Toluene
Soaking Time
Proppant
15 Hours
40/70 Mesh
Barnett
As received i d
Water soaked
Oil
Oil soaked
k d
Haynesville
Marcellus
26
Fluid/Rock Interaction Tests – Good Quality Samples
Fluid/Rock Interaction Tests: Poor Quality Samples
Proppant
pp
Embedment Comparison
p
100 M h
100 Mesh Water Soaked – Good RQS
h
Mix h = 131 m
Water Soaked – Poor RQS
Q
40/70 Mesh h = 105 m
Proppant
pp
Embedment Comparison
p
100 M h
100 Mesh Oil Soaked – Good RQS
Mix h= 85 m
Oil S
Soaked
k d – Poor
P
RQS
40/70 Mesh h = 91.4 m
Sources of Fracture Conductivity Impairment
H =50 m
H
W = 350 m

W





Depth of fluid imbibition
Embedment depth
Volume of extruded material
Chemical reaction between fluid and mudstone
Mobilization of extruded material
How to overcome damage
g
 Generate proppant free
pathways
Fracture Conductivityy of Pillar Tests Soaked with Water
Average Embedment 116.4 m (28 %)
Fluid/Rock Interaction Pillar Distribution Tests
What is the Impact of fracture conductivity in
production?
To answer this question we made sensitivity runs
varying:
 Reservoir permeability from 10 nD to 1000 nD
 Fracture conductivity values from 0.5 md
md-ft
ft to
1000 md-ft
And estimating gas production for:
 Fracture half-length 1000 ft
 Fracture height 200 ft
 Propped
pp width 0.06 in.
200 ft
1000 ft
Impact of fracture conductivity in production
For k = 1000 nD FCD significant production
For k = 10 nD
FCD no production impact
T
IMPAC
Conclusions
Non-propped fractures conductivity tests
depending of the fracture roughness, self propped
fractures can have similar fracture conductivity values
as propped
d fractures,
f t
but
b t conductivity
d ti it decreases
d
att
much faster rate.
Conclusions
Propped Fracture Tests
Sources of fracture conductivity impairment are:
Depth of fluid imbibition,
volume of extruded material,
chemical reaction between fluid and mudstone, and
 mobilization of the extruded material
Creep ttests
C
t ((constant
t t stress
t
tests)
t t ) Fines
Fi
plugging
l
i the
th pore space are
the main cause of fracture conductivity impairment
Impact of changing proppant size in fracture conductivity depends on
the rock quality