1 Five Things I Wish a Geologist Had Taught Me Mike Vincent [email protected]Fracwell LLC Microseismic image: SPE 119636 Confessions of a Frac Engineer • G&G folks often have tremendous advantages over PEs – Familiar with how rocks break – Understand reservoir laminations and compartments – Ability to visualize proportions – Less “contaminated” by simplified models and established rules of thumb – Many others • I’ve screwed up a bunch of fracs in the past. I wish you had helped me. • There are more than 5 things I failed to understand, but that is all I have time to review today! Proposal
• G&G folks often have tremendous advantages over PEs
– Familiar with how rocks break
– Understand reservoir laminations and compartments
– Ability to visualize proportions
– Less “contaminated” by simplified models and established rules of
thumb
– Many others
• I’ve screwed up a bunch of fracs in the past. I wish you had helped me.
• There are more than 5 things I failed to understand, but that is all I
have time to review today!
Proposal
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SPE 128612
Do we model fracs correctly?
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We picture fracs as perfect vertical planes without restriction to hydrocarbon flow
Fracs are very narrow ribbons, massively long!
Frac length frequently
thousands of times greater than
the wellbore diameter
We have created hydraulic fracs 2200 ft half-length but less than 0.1 inches wide
NEVADA TEST SITE - HYDRAULIC FRACTURE MINEBACK
Observations of Fracture Complexity
Physical evidence of fractures nearly always
complex
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Multiple
Fractures• Initiation At Perforations
– Multiple Perforations
Provide Multiple Entry
Points For Fracture
Initiation
– Five Separate
Fractures Are Visible
In These Fractures
Initiated From
Horizontal Wellbore
– 12 Perforations Total
• 6 Top & Bottom
I would have modeled/predicted a single frac with much
higher conductivity than 5 narrow fracs added together
[This actually is a bad outcome!]
NEVADA TEST SITE
HYDRAULIC FRACTURE MINEBACK
Multiple Strands in a Propped Fracture
(Vertical Well)
These fractures are narrow, you are looking at an angle to the exposed frac face
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Mesaverde MWX test, SPE 22876
Physical evidence of fractures nearly always
complex
Multiple Strands in a Propped Fracture(Vertical Well)
� 7100 ft TVD [2160m]
� 32 Fracture Strands Over 4 Ft Interval
� HPG gel and fine (pulverized) sand residue glued some core together (6-7 elapsed years)
� Gel residue coated every surface
� A second fractured zone with 8 vertical fractures in 3 ft interval observed 60 feet away (horizontally)7
Physical evidence of fractures nearly always complex
NEVADA TEST SITE
HYDRAULIC FRACTURE MINEBACK
Fracture Complexity Due To Joints
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Laminated on every scale?
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Figure 2 – On every scale, formations may have laminations that hinder vertical permeability and fracture penetration. Shown are thin laminations in the Middle Bakken [LeFever 2005], layering in the Woodford [outcrop photo courtesy of
Halliburton], and large scale laminations in the Niobrara [outcrop and seismic images courtesy of Noble]
SPE 146376 (pending publication)
Woodford Shale Outcrop
Some reservoirs pose
challenges to effectively
breach and prop through
all laminations
Rational Expectations?
Our understanding of frac barriers and kv should
influence everything from lateral depth to frac fluid type, to implementation
Narrower aperture plus significantly higher stress in
horizontal steps?
Failure to breach all lamina?
Will I lose this connection due to
crushing of proppant in horizontal step?
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Fractures Intersecting Stacked Laterals
Modified from Archie Taylor SPE ATW – Aug 4 2010 11
23 ft thick Lower Bakken Shale
Frac’ed Three Forks well ~1MM lb proppant in 10 stages
1 yr later drilled overlying well in Middle Bakken; Kv<0.000,000,01D (<0.01 µD)
kv/kh~0.00025 even after fracing!
Lateral separation 250 feet at
toe/heel, crossing in middle
Inability to create an effective, durable fracture 30 feet tall?!
Drill redundant well in each interval since frac has inadequate vertical penetration/conductivity?!
Bakken – Three Forks
Uniform Packing Arrangement?
Is this ribbon laterally extensive and continuous for
hundreds of meters as we model?
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Pinch out, proppant
pillars, irregular
distribution?
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With what certainty can we explain this production?
SPE 106151 Fig 13 – Production can be matched with a variety of fracture and reservoir parameters13
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Cu
mu
lative
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(M
Mscf)
Actual Production Data
Nice match to measured microseismic, eh?
SPE 106151 Fig 13 – Production can be matched with a variety of fracture and reservoir parameters14
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lative
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ction
(M
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Actual production data
Long Frac, Low Conductivity 500' Xf, 20 md-ft, 0.5 uD perm, 23 Acres 4:1 aspect ratio
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Is this more accurate? Tied to core perm
SPE 106151 Fig 13 – Production can be matched with a variety of fracture and reservoir parameters15
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(m
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mu
lative
Pro
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ction
(M
Mscf)
Actual production data
Long Frac, Low Conductivity
Medium Frac, Low Conductivity
500' Xf, 20 md-ft, 0.5 uD perm, 23 Acres 4:1 aspect ratio
100' Xf, 20 md-ft, 5 uD perm, 11 Acres 4:1 aspect ratio
Can I reinforce my misconceptions?
SPE 106151 Fig 13 – Production can be matched with a variety of fracture and reservoir parameters16
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Production Days
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(m
cfd
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Cu
mu
lative
Pro
du
ction
(M
Mscf)
Actual production data
Long Frac, Low Conductivity
Medium Frac, Low Conductivity
Short Frac, High Conductivity, Reservoir Boundaries
500' Xf, 20 md-ft, 0.5 uD perm, 23 Acres 4:1 aspect ratio
100' Xf, 20 md-ft, 5 uD perm, 11 Acres 4:1 aspect ratio
50' Xf, 6000 md-ft, 10 uD perm, 7 Acres 4:1 aspect ratio
• History matching of production is surprisingly non-unique.
• Too many “knobs” available to tweak
• We can always blame it on the geology
Even if I “know” it is a simple planar frac, I cannot
prove whether it was inadequate reservoir quality, or inadequate completion with a single well
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Removing the Uncertainty
• If we require a production match of two different frac designs, we remove many degrees of freedom – lock in all the “reservoir knobs”!
– The difference in production must be explained with the difference in the FRAC descriptions, not the reservoir description, right?
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We are 99.9% certain the Pinedale Anticline
was constrained by proppant quality
Effect of Proppant Selection upon Production
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100
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900
LL3
LL2
LL1
MV5
MV4
MV3
MV2
MV1
MV0
Avera
ge
Reservoir Sub-Interval (Lower Lance and Mesa Verde)
Pro
duction R
ate
100 d
ays p
ost-
frac (
mcfd
)
Versaprop
CarboProp
ISP-BS
ISP 20/40
Averages based on 95 stages ISP-BS and 54 stages ISP 20/40
SPE 106151 and 108991
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Evidence to convince your engineer
– SPE 119143• 200 fields in which alternative frac designs were
compared
– SPE 134330• 143 fields in which refrac results were published
– Compelling evidence that formations are often more permeable than we think and fracs are not optimized
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Can we learn from refracs?
Pagano, 2006
– Gas Condensate wells in DJ Basin – up to 5 restimulations
– Rangely oilfield – 1700 refracs 1947-1989. Most wells have
received 3-4 refracs yet remain viable restimulation candidates.
– Pembina oilfield – Conductivity was understood to degrade over
time, with production falling to unstimulated rates in 6-7 years.
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Does Conductivity Degrade?
McDaniel , SPE 15067
All published lab data show proppants continue to crush, compact, rearrange over
