Fracture Initiationfrom Perforations

Andy Martin & HarveyWilliams

IPS 14-02

IPS-14-0212 May 2014, 2

Agenda

• Perforating objectives for fracture stimulation

• Modelling Fracture Initiation

• Penetration

• Clean Perforations

• Direction

• Conclusions

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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)

IPS-14-0212 May 2014, 24

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?