refracs: what can we decipher? - mike vincent
Post on 18-Jan-2015
1.113 Views
Preview:
DESCRIPTION
TRANSCRIPT
1
Mike Vincent
Insight Consulting
mike@fracwell.com
303 568 0695
Refracs –
What can we decipher?
SPE 134330 & 136757
Fracwell
LLC
Outline
Introduction
• Non-unique solutions, uncertainty, value of field data
Refrac Field Results
• Refrac definition
• History of restimulation
• Why do refracs work?
– Mechanisms; cause/effect
– Field examples
• Why do refracs fail?
Interpretations and Recommendations
2
Can I reinforce my misconceptions?
SPE 106151 Fig 13 – Production can be matched with a variety of fracture and reservoir parameters6
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 100 200 300 400 500 600
Production Days
Sta
ge
Pro
du
ctio
n (
mcfd
)
0
20
40
60
80
100
120
140
160
180
200
Cu
mu
lative
Pro
du
ctio
n (
MM
scf)
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
If I don’t uniquely match this, can
I trust my refrac interpretation?
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?
7
3
Recent Recent attempts to history-match field production:
• SPE 119143 – summary of 200 published field trials in
which initial frac designs were altered
• SPE 134330 – summary of 143 published reports of the
outcome of refrac attempts (worldwide)
• SPE 136757 – evaluation of ~ 100 Bakken refracs
– Direct search - minimizes “publication bias”
– First field to allow evaluation of proppant durability on refrac success
• There are many surprising results that are difficult to
explain with traditional models
• “It’s awfully dark down there”
• Fracs are not as efficient/durable as we anticipate
• Keep an open mind, dig, challenge.
• None of us have it figured out. Consider outlandish ideas!
Refracs
My Definition of Refrac
• A second propped fracture treatment (with production data between!)
• Also tri-fracs, quads-, and “cinco-de-fraco” restimulations
• I have excluded a large dataset where propped fracs
improve previous acidized or unpropped initial treatments
– What can we learn about durability of unpropped portions of the
frac?
Goals
• Identify restimulation opportunities
• Improve initial designs
• Understand fracture and refrac mechanisms
• Improve production models and frac models
4
History1953
Observations:
May recover or exceed initial
productivity!
Decline rate also reduced!
1955 – Refrac
and Tri-Frac
Adapted from Garland, 1957
Sallee&Rugg,1953
Does this outcome fit your
intuition or model?
– Through 1970
• 35% of the 500,000 stimulation treatments were refracs
– 1996
• Only 2-3% of current stimulation activity was refracs
– Why?• Did we improve design, implementation, durability of initial frac
treatments?
• Did technological evolution cease?
• Did economic parameters change?
• Are we no longer staffed to analyze refrac opportunities?
• Did refracturing fall from vogue and become lost art?
• Are refracs not as effective as initially believed?
– Current: Desire to understand refracturing
History
5
Where Have Refracs Worked?Well Types
Oil Wells (under primary depletion, waterflood, or EOR)
Condensate Wells
Gas Wells
Gas Storage Wells
Water Production Wells
Water Injection Wells
Steam Injection Wells
Huff-n-Puff , cyclic injection/withdrawal Wells
Disposal Wells
Formation Types
Carbonates, limestones, dolomites, chalks, evaporites
Sandstones, cherts, siliceous diatomites
Coal (CBM), immature ductile shales, brittle shales
Conglomerates, unconsolidated formations, siltstones
16-page Appendix is attached to
SPE 134330 describing all field
examples
– Immediately post-frac
• Unsuccessful implementation
• To achieve new entry points, diversion, reorientation
– Somewhat later
• Most common published examples are 1-10 years later
– Much Later
• >20 years, Clinton Sand, high perm oil, Ohio
• >30 years, Mesaverde tight gas sand, Colorado
• >30 years, Rangely Field, high perm oil, water + CO2
flood, Colorado
• >40 years, Pembina mature waterflood, Alberta
• >30 years, Medicine Hat, Milk River shallow gas
– Ideas available on the theoretically “optimal” time to refrac,
but we need to discuss mechanisms first!
When have Refracs been Performed?
6
Refrac after 25 years of Depletion?15 refracs (shallow gas – Medicine Hat & Milk River)
All 15 responded to restimulation
Average increase 600-900%
6 of 15 achieved higher production than peak 25+ years prior
4 of 15 achieved rates within 25% of peak IP
Rate prior to Refrac
First 3 months, Initial Frac
3 month average, Post Refrac
Adapted from Gutor, 2003
Observation:
Excellent
success
despite
decades of
production.
Why Do Refracs Work? (mechanisms)
Refrac success (worldwide) has been attributed to:
• Enlarged frac (more reservoir contact)
– Improved pay coverage (add pay in vertical wells)
– Better lateral coverage (horizontal wells)
• Increased frac conductivity
– Restore conductivity lost – frac degradation
– Address unpropped/poorly propped portions
• Improve wellbore-to-frac connection/conductivity
• Reorientation
• Use of more suitable frac fluids
• Re-energizing natural fissures
• Other mechanisms
7
Improved Reservoir Contact
• Bypassed Pay in Vertical Wells
– Where radioactive tracers or detectable proppants indicated missed
opportunities, refracs are frequently successful
Adapted from Hecker, 1995
Refrac contacted initially bypassed pay
Improved Reservoir Contact• Bypassed Pay in Vertical Wells
– 50 discrete sands in Pinedale [Huckabee 2005]
• Can we touch it all with 15-20 stages?
– ~26 sand intervals in Piceance
• 28% of those stages fail to produce measurable gas? [Esphahanian 1997]
• Limited entry didn’t induce effective diversion? [Craig & Odegard 2008]
– 30-40 sand intervals in Jonah?
• 35 to 40% fail to contribute meaningfully [Eberhard 2003]
– Almond, Cotton Valley, Delaware, Red Fork
• In 40% of wells, at least one targeted interval failed to accept any RA tracer
[Fisher 1995]
• Touching Pay is Job #1– If kv/kh is tiny, you MUST create conductive, durable, vertical breach of
these horizontal laminations
– Despite what a simple model will predict, not all gas molecules are
hydraulically connected to a perforation
– Is bypassed pay a primary refrac opportunity?
8
Improved Reservoir Contact
• Improved Coverage of Horizontal Laterals
– Where radioactive tracers or detectable proppants indicated missed
opportunities, refracs are frequently successful
Adapted from Lantz, 2007
• Montana Bakken, cemented laterals believed drilled for longitudinal growth
• Initial fracs ~300,000 lb 20/40 RCS
• RA tracer showed incomplete coverage
• Add perfs, refrac 600,000 lb 20/40 sand, 10 ppg slugs, ball sealers
Improved Reservoir Contact
Adapted from Lantz, 2007
Refrac reduced GOR,
increased oil rate and reserves
• Lower breakdown pressures, but 50% greater net pressure
• We should revisit this issue!
• Oil rates up, GORs down
• Refracs diverted into undrained areas of the reservoir
• EUR increased 1,300,000 bbls in 16 refractured wellbores
• 1 mechanical problem, but 16 of 17 successful (94%)
9
Refrac on a Schedule?
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.
Does Conductivity Degrade?
0
0.2
0.4
0.6
0.8
1
0 15 30 45 60 75
Perm
eab
ilit
y R
ati
o
Days at Constant Stress
IDC at 10,000 psi (69 MPa)
LWC at 10,000 psi (69 MPa)
Sand at 5000 psi (35 MPa)
Cobb, 14133
200F, 5000/10,000 psi [93C, 35/69 MPa]
All non-corrodible surfaces, prop in
Teflon tube, continuous flowing 2% KCl
McDaniel , 15067
275F, 8000 psi [135C, 55MPa]
showed importance of using silica
saturated, deoxygenated brine
10
100
1000
10000
0 10 20 30 40 50
Co
nd
ucti
vit
y (
md
-ft)
Days at Constant Stress, 8500 psi
IDC - Intermediate Density Ceramic
Proflow - Precursor to LWC
RCS - Resin Coated Sand
Ottawa Sand
0
20
40
60
80
100
0 30 60 90 120 150 180 210 240 270
% O
rig
inal
Co
nd
ucti
vit
y
Days at Constant Stress, 5000 psi
20/40 Sand at 75F
10/20 Sand at 250F
Hahn, SPE Drilling 1986
300F, 8500 psi [149C, 59 MPa]
Teflon tube, continuous flowing 2% KCl,
Non-silica saturated
Montgomery (12616) 1984
75/250F, 5000 psi [23C/121C, 34 MPa]
API “short term” cell: Metal plates,
continuous flowing 2% KCl,
Non-silica saturated
25
Does Conductivity Degrade?
Previous testingHandren 110451
250F, 6000 psi [121C, 41MPa]
Modern conductivity cell, Ohio Sandstone
Deoxygenated, Silica Saturated 2% KCl,
Does Conductivity
Degrade?
All
proppants
degrade, but
at different
rates.
Is replacing
degraded
proppant a
major factor
in refrac
success?
11
Perhaps this makes sense?
Pagano, 200627
Provocative Statements• Refrac DJ with minimal data
– >5000 refracs performed
– Few wells individually metered, even fewer with production log
or single-zone test (comingle J Sand, Codell and Niobrara)
– >8 papers written – arguing different mechanisms that account
for success
– We don’t know where, why, or how these refracs work
• No correlation between reorientation and production? (Wolhart)
• Which do you agree with?
– “Engineering malpractice”
– “Statistically validated approach to blanket refrac”
– “Honestly? Do this 5000 times without actually trying to
investigate whether we can address durability?”
– “Financially prudent approach”
12
Proppant Durability Affect Refracs?
• SPE 136757
– Examines refrac success of ~100 horizontal wells in
Bakken
– Large number of wells completed with:
• Sand
• RCS
• Ceramic
– Large number of refracs attempted on each type
• ~90% success restimulating Sand or RCS completions
• <50% success restimulating wells initially completed with
Ceramic
– More durable proppants appear to delay or avoid the
need to restimulate this field
Increase Conductivity in Refracs?Dozens of examples in literature
Shaefer, 2006 – 17 years later,
tight gas
0
500
1000
1500
2000
2500
3000
3500
Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01
Ga
s R
ate
, M
CF
D
0
50
100
150
200
250
300
350
400
450
500
Wa
ter
Ra
te,
BW
PD
Gas
Water
Initial Frac in
1989:
48,000 lb 40/70
sand + 466,000
lb 12/20 sand
May 1999 Frac:
300,000 lb 20/40
LWC
May 1995 Frac:
5,000 lb 100 mesh
+ 24,000 lb 20/40
Sand
Vincent, 2002 – 9 years later,
CBM
0
500
1000
1500
2000
2500
3000
3500
4000
May-84 May-86 May-88 May-90 May-92 May-94 May-96 May-98 May-00
Date
Pro
du
cti
on
fro
m F
rac
ture
(b
fpd
) Original Fracture (20/40 Sand)
Phase I refrac (20/40 Sand)
Phase III refrac (16/20 LWC)
Incremental
Oil Exceeds
1,000,000
barrels
Incremental
Oil exceeds
650,000
barrels
First
Refrac
Second
Refrac
Pospisil, 1992 – 6 years later,
20 mD oil
0
500
1000
1500
2000
2500
Sta
biliz
ed
Ra
te (
MS
CF
D)
Pre Frac 10,000 gal
3% acid +
10,000 lb
glass beads
80,000 gal +
100,000 lb
20/40 sand
75,000 gal +
120,000 lb
20/40 ISP
Ennis, 1989 – sequential
refracs, tight gas
0
20
40
60
80
100
120
Well A Well B Well C Well D Well E
Pro
du
ctio
n R
ate
(to
nn
es/d
ay)
..
Initial Frac
Refrac
Dedurin, 2008, Volga-Urals
oil
30
13
Refrac Reorientation
Barnett - Cipolla, 2005
• Refrac Reorientation Documented in:
– Lost Hills Diatomite
– Austin Chalk
– M. Bakken Dolomite
– Codell, DJ Basin
– Barnett Shale
– Van oilfield
– Ansai oilfield
– Daqing oilfield
– Xin Zhan field
• Diversion/reorientation evidence:
– Mounds cuttings disposal site
– Black Warrior CBM
– Undisclosed locations
31
Cross Sectional View
0 100 200
Xf, ft
Core
Projections
2400
2500
2600
2700
2800
2900
-50 0 50 100 150 200 250 300 350
GR & Hor. Dist., ft
De
pth
Core#
4
Core#1
Fracture
Intersections
Core#3
GR and Hor. Dist.,
ft
Mounds Wilcox Interval Tiltmeter & µS Mapping
No hydraulic
fractures present
in Sidetrack #3,
confirming
vertical
containment.
-100
-75
-50
-25
0
25
50
0 25 50 75 100 125 150 175
Easting (feet)
No
rth
ing
(fe
et)
Wellheads
Perforation Locations
Wellbores
Core
Frac Intersections
Mapped Fractures
Average azimuth
N 71° W ± 11°
Sidetrack #1
Sidetrack #4
Note: Dips of vertical fracs are not
properly represented on this plan view.
Plan View
- 5 diagnostic injections and 17 cuttings slurry
injections
- Core #1 detected ~20 hydraulically induced fractures
- Core #3 detected no hydraulically induced fractures
- Core #4 detected ~9 hydraulically induced fractures
Sidetrack 4 ABOVE
fracture center
Case C-01 See also: SPE 63032
14
Mounds
Cuttings
Injection
Reference: 77553, after
Moschovidis, SPE 59115,
63032, 48987
• Core through verified multiple fracs in recovered core
• Core above Wilcox confirmed containment in mapped interval
Why Do Refracs Work? (mechanisms)
Refrac success (worldwide) has been attributed to:
• Enlarged frac (more reservoir contact)
– Improved pay coverage (add pay in vertical wells)
– Better lateral coverage (horizontal wells)
• Increased frac conductivity
– Restore conductivity lost – frac degradation
– Address unpropped/poorly propped portions
• Improve wellbore-to-frac connection/conductivity
• Reorientation
• Use of more suitable frac fluids
• Re-energizing natural fissures
• Other mechanisms
– Fracturing past condensate block, inducing complexity, rearranging
existing proppant pack, better containment of refrac, etc
15
Why Do Refracs Fail? (poorer candidates)
Refrac failure (worldwide) often attributed to:
• Low pressure
– depleted wells (limited gas reserves)
– poor recovery of frac fluids
• Inadequate reservoir quality
• Diagnostics indicated drainage to reservoir boundaries
• Undesirable existing perforations
• Poor mechanical integrity
• Failure to clean out well prior to restimulation
• Inadequate procedures to select refrac candidates
– Poor wells often make poorest refrac candidates
– Unless there was a failure in initial frac design or implementation
35
Additional Examples
Horizontal Well Refracs
16
Bakken Refracs (Lantz, 2007: 108117)• Montana, cemented laterals believed drilled for longitudinal growth
• Initial fracs ~300,000 lb 20/40 RCS
• RA tracer showed incomplete coverage
• Add perfs, refrac 600,000 lb 20/40 sand, 10 ppg slugs, ball sealersupper track of Figure 4.
The effect of depletion was observed in the treating records, as breakdown pressures averaged 669 psi lower than initial
treatments. However, net pressure generated during the refracs was approximately 50% greater than during the initial fracs.
Figure 4 – Tracer logs in horizontal well indicate coverage was increased by refrac. [Figure adapted from Lantz, 2007]
Tracer from original frac▲
▼Tracer from refrac
• Lower breakdown pressures, but 50% greater net pressure
• Oil rates up, GORs down
• Refracs diverted into undrained areas of the reservoir
• EUR increased 1,300,000 bbls in 16 refractured wellbores
• 1 mechanical problem, but 16 of 17 successful (94%)
Observations:
Can refrac into new rock from
cemented wellbores
37
Bakken Refracs (Dunek, 2009: 115826)• Uncemented liner. N-S oriented lateral. Surface tiltmeter mapping
• Unintentional termination of frac job (wellhead isolation tool failure)
– 3892 bbl crosslinked fluid and 296,000 lb proppant at 48 bpm
• 2nd stimulation treatment 6 weeks later
– 6533 bbl slickwater and 193,000 lb proppant at 61 bpm
Transverse: 45% heel
Longitudinal: 30%
Horizontal: 10%
Oblique: 15%
Transverse: 45% toe, mid
Longitudinal: 35%
Horizontal: 20%
Observations:
Diversion/ Initiation at new locations
Both Transverse and Longitudinal Growth
17
Bakken Refracs (Eberhard, 2008: WBPC)
Cemented laterals initially treated with sand/RCS
• Reperf/jet new entry points
• Diversion slugs
• 100% success rate– 30 days prior – 46 bopd
– 30 days post refrac – 144 bopd
Uncemented Liners initially treated with sand/RCS
• Retreat existing perfs
• 87% success rate (27 wells)– 30 days prior – 64 bopd
– 30 days post refrac – 122 bopd
Observations:
Adding entry points helps.
Initial cemented laterals failed to drain
all rock
Bakken wells frac’ed with sand usually
benefit from refrac (~90% of time)
39
Bakken Refracs (Besler 2007/2008,
SPE 110679 + 2008 WBPC)
Bakken wells initially stimulated with ceramic
• Only ~50% success rate with refracs using ceramic– Refrac success appears to correlate with wells in which RA tracer indicated
poor diversion
– In pre-refrac cleanouts, only minimal quantities of ceramic proppant
recovered from wellbore
Observations:
Less need to refrac if wells treated with ceramic?
Perhaps due to reduced proppant flowback or better durability?
40
18
Bakken Refracs (Phillips 2007 SPE
108045)
Bakken wells initially stimulated with ceramic and
XLG
• Showed 1st month benefit refracturing with sand/slickwater
41
Bakken Refracs (Operator B)
• 3 Wells initially stimulated with 20/40 ceramic in XLG
• Restimulated 13-39 months later with >200,000 lb 30/50 or
40/70 Ottawa (much information unavailable via public data)
• 2 of 3 wells subsequently TA, but did give short term benefit.
0
20000
40000
60000
80000
100000
120000
0 12 24 36 48
Cu
mu
lati
ve O
il P
rod
uct
ion
, Bar
rels
Months on Production
Well B-1
Well B-2
Well B-3
Refrac
Refrac
Abandon
Trifrac
Abandon
Refrac
Sand refracs of initial ceramic
completions have been
successful, but 2 of 3
abandoned?
19
0
10000
20000
30000
40000
50000
60000
0 10 20
Cu
mu
lati
ve O
il P
rod
uct
ion
, Bar
rels
Months on Production
Well C-1
Well C-2
Refrac
Refrac
Bakken Refracs (Operator C)
• 2 wells initially stimulated with sand > 1,000,000 lbs (staged)
• Restimulated 8-11 months later, slickwater with 100,000 lb
30/50 lightweight ceramic (bullhead; overflushed)
Limited data, but:
100,000 lb LDC refracs in
slickwater diagnostic plots
similar/superior to initial fracs
0.00001
0.00010
0.00100
0.01000
0 0.5 1 1.5 2 2.5 3 3.5
1/B
OP
M
Square Root of Months on Production
Well C-1
Well C-1 Refrac
Well C-2
Well C-2 Refrac
Saskatchewan Bakken Refracs
Vincent, 2010 - 136757
• 9 refracs identified in Viewfield area
• 8 initially completed barefoot with 7-8 stages coiled tubing
• 8 recompleted uncemented, ball activated sliding sleeves
• 1 recompleted-cemented liner, abrasive jet, annular refrac
• All 9 show oil increase. Watercut down in 7 of 9 refracs!
0
200
400
600
800
1000
1200
1400
0
20
40
60
80
100
120
140
160
180
200
0 10 20 30 40 50
GO
R (m
cfd
/bb
l)
BO
PD
an
d W
ater
cut
%
Months on Production
BOPD
BOPD normalized for downtime
Watercut
GORRefrac
Observations on this well• Oil increased from ~25 to
~140 bopd
• Water decreased from ~250
to <100 bwpd!
• GOR temporarily dropped
44
20
Restimulation of Gas WellsDick Leonard, ProTechnics
Expanding Shale Plays – 2009. PNR Energy
Forum, Brookhaven College May 28, 2009
Barnett Shale
Refracture Treatment
• Min/Max stress are very similar in the Barnett.
• There are now over 4000 traced HZ wells in the Barnett,
about 50% show anomalies (unstimulated perfs, cement integrity,
casing problems)
• “Refracs are, and will become, critical to these shale plays”.
It appears that we are not draining very far past the
fractures.
Refracturing of BarnettDick Leonard
Tri
21
Refracturing of BarnettDick Leonard
Barnett Refrac
SPE 131783 Curry, Maloney (Range Resources)
• Denbury Winston A3 well:
– Original Completion:
– 3000 ft cemented lateral
– Original perfs spaced at 450 ft
– Restimulated 2007
– Added intermediate perforations as shown on next page
– Two stage refrac, placing 855klb proppant
– Stage 1: 240 klb 40/70 + 290 klb 20/40
– Stage 2: 220 klb 40/70 + 105 klb 20/40
– Slickwater at 102 bpm
– RA tracer shows diversion of treatment into new areas
– Incremental EUR 1.0 BCF
53
22
Refracturing of BarnettDick Leonard
Green bars
denote new
perf clusters
evenly
spaced
between old
existing
perfs. Note
that on this
stage, the
new perfs
took most of
the refrac
Apparent
stress
diversion.
This is one
of the best
cases
This well
was
identified as
the Denbury
Winston A3
well in SPE
131783
Refracturing of BarnettDick Leonard
A packer
was set to
isolate the
lower (red)
stage.
It appears
the middle
green new
perfs took
proppant,
but
upper/lower
did not?
This well
was
identified as
the Denbury
Winston A3
well in SPE
131783
23
Refracturing of BarnettDick Leonard
Marcellus Refrac - Public
SPE 131783 Curry, Maloney (Range Resources)
• Range Nancy Stewart 4H well:
– Original Completion:
– 3000 ft cemented lateral
– 100 ft perf spacing
– 8 stages, placing 1.9 mmlb 100 mesh + 1.1 mmlb 30/50 sand
– Crosslinked gel & slickwater used at average of 54 bpm
– Restimulated Aug 2008
– Added “intermediate perforations”
– Single stage refrac, placing 880klb 100 mesh + 390klb 30/50
– Slickwater at 131 bpm
– RA tracer shows diversion of treatment into new areas
– Incremental EUR 0.8 BCF
57
24
Marcellus Refrac
SPE 131783 Curry, Maloney (Range Resources)
• Range Nancy Stewart 4H well:
– Incremental EUR 0.8 BCF
58
New perfs appeared to preferentially
receive RAT in refrac
Refracturing of
Marcellus
Buddy Woodruff, ProTechnics
SPE ATW, Banff, May 3 2011
Original FG = 0.99 psi/ft
Refrac FG 1.05 psi/ft
Orig EUR 1.7 BCF
Post ReFrac EUR 2.5 BCF
25
– I am aware of 7 refracs performed in EF
• Swift
• Pioneer
• Results are not yet disclosed
• Also in Eagle Ford, hesitation fracs have been shown by
some operators to have induced diversion via
microseismic mapping
Eagle Ford
– Immediately post-frac
• Relax-a-frac? SPE 136873 Eagle Ford
Eagle Ford Relax-a-Frac
26
– Immediately post-frac
• Relax-a-frac? SPE 136873 Eagle Ford
Eagle Ford Relax-a-Frac
Successful refracs have been
performed in Barnett, Woodford,
Eagle Ford, Bakken, Marcellus,
Haynesville, Niobrara, Spraberry,
Wolfcamp…
What did we miss the first time?
27
– Standard models fail to predict refrac performance
• Multiple mechanisms
• Models fail to recognize compartmentalization, degradation, realistic
conductivity, etc.
– Artificial Intelligence, Neural Nets
• Excellent success in some fields (Shelley, 1999)
• Dismal failure at predicting success in others
• Some refracs have worked when all diagnostics said they shouldn’t!
– Reorientation
• Beneficial when it occurs (except in some waterfloods)
• Is not necessary for refrac success in many fields
– Refracs have worked in most reservoir types
• And there are examples of failures in most, also!
– Well design
• We need wells that can be cost-effectively isolated and restimulated
Comments
65
– No “magic bullet” was apparent. However, most successful refracs have
incorporated:
• Larger proppant mass
• Improved proppant quality
• Higher proppant concentrations (if placed with crosslinked fluids)
– Adding perfs (if pay was missed) is valuable. Diversion!
– Proppant durability is an issue
– Some refracs clearly touch new rock
• Some refracs do not, yet are still economic
– Good wells are often the most economic refrac candidates!
• Refrac “dogs” if design or implementation failure on initial frac
– Even the best wells can be improved! (corroborates SPE 119143)
• Non-optimal initial fracs, proppant degradation, or reorientation “gift”
– Refrac candidate selection takes effort
• Not as “routine” as drill & complete
• Outstanding economic opportunities available
Some Interpretations 134330 & 136757
66
28
Human beings, who are almost unique in
having the ability to learn from others,
are also remarkable for their apparent
disinclination to do so.
Pertinent Quotation
Douglas Adams (1952-2001)
English writer
top related