ips 14-02 fracture initiation from perforations · 2017. 5. 22. · title: microsoft powerpoint -...
TRANSCRIPT
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Fracture Initiationfrom Perforations
Andy Martin & HarveyWilliams
IPS 14-02
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IPS-14-0212 May 2014, 2
Agenda
• Perforating objectives for fracture stimulation
• Modelling Fracture Initiation
• Penetration
• Clean Perforations
• Direction
• Conclusions
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IPS-14-0212 May 2014, 3
Perforating Objectives for Fracturing
• Make frac jobs more effective
– Lower breakdown pressures
– Lower treatment pressures with better treatmentrates
– Controlled frac placement
• All of this leads to better production
• Also helps avoid disasters like aborted jobs
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Perforating Objectives
• Perforations shouldminimize:
– Near wellbore pressuredrop
– Perforation friction
– Tortuosity
– Micro-annulus pinchpoints
– Multiple competingfractures
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Well Direction and Gun Phasing
Gun phasing andinterval perforatedshould be basedon well directioncompared to thepreferred fractureplane
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Hydraulic Fractures in HorizontalWells
Transverse fracsTransverse fracsLongitudinal fracsLongitudinal fracs
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What can we control?
• Size and type of gun
• Penetration (type of charge)
• Casing entrance hole
• Shot density
• Shot phasing
• Interval length
• Gun orientation
Focus has been casing entrance hole
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Casing Entrance Hole
• EH size about 8 to 10 times proppantdiameter to prevent bridging
• Consistent EH for accurate limited entrydesigns
• 40% variation in EH results in 120%increase in pressure drop
(from SPE 83950)0%
10%
20%
30%
40%
50%
0% 20% 40% 60% 80% 100% 120% 140%
EH variation vs Error inPressure Calculation
EH
varia
tion
Error in pressure
0.2369
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Minimizing Casing Entrance HoleVariation
• Use largest gun possible to reduce waterclearance
• Centralize gun
• Design shaped charge for minimum variation evenacross large water clearances
Std Frac charge New Frac charge
Best Frac ChargeBest Frac Charge
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What do the models say?
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• Modeling of fracture initiation fromcemented perforated wellbore providesinsight into direction and penetration
Modelling Fracture Initiation
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Modelling Fracture Initiation
As pressure increases, transversefractures propagate from
perforations
• Models of cased and cemented perforations
can help determine well direction and
perforation direction to minimize fracture
initiation pressure.
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• Simple calculations of
hoop stress for horizontal
well with various
casing/cement conditions
• Simulation shows that
there can be a large
stress difference between
top and bottom
Hoop Stress & Cement
Stress estimation around casing vsvariation cement/casing situations
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• So far single perforationsare modelled
• Detail geomechanicsrequired
• Detailed cement qualityrequired
• Need perforation shape
• Assumes cleanperforations
Model Limitations
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What about penetration?
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“Penetration is Not Important.All We Need is 6 to 8 in.“
• “All DP shaped charges shoot more
than 8 in. Just look at the API data.”
• “We know that we need to get
beyond near-wellbore stress,
formation damage and break outs.
But all we need is about 1 BH
diameter.”
• It is amazing how many Frac
Engineers do not know that
penetration is affected by UCS and
Stress
Up to 5-inch damage (SPE 112862)
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Importance of KnowingPenetration in Rock
• I want >6”penetration in20,000 psi UCSrock. Whichshaped chargeshould I use?
• API concretedata misleading
• Rock modelimportant
Rockmodel
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What about clean perforations?
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What about Clean Perforations?• Enable injection to
start deeper information, avoids nearwellbore damagedzone
• Fractures may notinitiate from pluggedperforations (see “bigblock” tests left)
• Clean perforationsallow fluid leak-off,increasing near-wellbore pressure priorto fracture initiation
(from SPE 143997)(from SPE 143997)
Plugged perforations NOfracture
Plugged perforations NOfracture
Clean Perforations with fracturepassing through perforations
Clean Perforations with fracturepassing through perforations
(from SPE20661)
(from SPE20661)
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Plugged perfs NO fracturePlugged perfs NO fracture
(from SPE20661)
(from SPE20661)
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Clean Perfs FractureClean Perfs Fracture
(from SPE20661)
(from SPE20661)
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What about direction?
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Gun Phasing and DirectionNear-vertical wells
• Fractures initiate
from perforations
aligned with
maximum stress
direction
• Best gun phasing
is 0° – 180° in max
stress direction
Perforations aligned withmaximum horizontal stressPerforations aligned with
maximum horizontal stress
(from SPE20661)
(from SPE20661)
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Gun Phasing and DirectionNear-vertical wells
• Fractures initiate
from perforations
aligned with
maximum stress
direction
• Best gun phasing
is 0° – 180° in max
stress direction
Perforations aligned withmaximum horizontal stressPerforations aligned with
maximum horizontal stress
(from SPE20661)
(from SPE20661)
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Perforations aligned with maximum horizontal stressPerforations aligned with maximum horizontal stress
(from SPE20661)
(from SPE20661)
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• Fractures initiate
from sand-face
when perforations
are misaligned
• Other gun phasings:
120° (at 1 ½ times
spf); 60° (at 3 times
spf)
Perforations misaligned withmaximum horizontal stress
Perforations misaligned withmaximum horizontal stress
(from SPE20661)
(from SPE20661)
Gun Phasing and DirectionNear-vertical wells
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Perforations not aligned with maximum horizontal stressPerforations not aligned with maximum horizontal stress
(from SPE20661)
(from SPE20661)
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What We Getwith 60° Phasing
Longitudinal fractures initiate firstTerminate about 2 wellbore diametersin vertical direction
– Extend along wellbore
– Initial pumped volumesdominated by longitudinal fracs
Transverse fractures initiate after
– Perpendicular to longitudinal
– Do not rotate from longitudinal
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What we getwith
60° Phasing
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Can We Do Better?
• Several experiments done inlarge blocks in a tri-axial stressframe to simulate horizontalwell
• Both DP and BH charges used
• Directional perforations aimedat the same transverse plane Transverse fracture fromdirected perforations
Transverse fracture fromdirected perforations
Result: Transverse fractures created
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Directional perforations in the same transverse plane
transverse fractures are created
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Conclusion
• Models of fraction initiation from perforationsshow importance of direction
• Models supported by practical experiments
• Data acquired from wells will help validate bothexperimental data and models
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Questions?