SPE Distinguished Lecturer Program

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The SPE Foundation through member donations and a contribution from Offshore Europe

The Society is grateful to those companies that allow their professionals to serve as lecturers

Additional support provided by AIME

Society of Petroleum Engineers Distinguished Lecturer Programwww.spe.org/dl 1

Hydraulic Fracturing Materials: Application Trends & Considerations

Harold D. BrannonBJ Services Company

Society of Petroleum Engineers Distinguished Lecturer Programwww.spe.org/dl

2

Outline• Hydraulic Fracturing• Fracturing Material Functions• Fracturing Fluids & Additives

– Recent trends– Emerging Technologies

• Proppants– Recent trends– Emerging Technologies

• Summary3

What is hydraulic fracturing?• A process of placing proppant into fractures created in oil

and gas zones to increase the flow of oil or natural gas to the wellbore.

• Fractures are created by pumping fluids at high pressures and rates.

• Proppant is added to the fluid, which when pumping has ceased, ‘props’ the fractures to keep them open.

• The propped fractures provide highly conductive flow paths for the hydrocarbons to reach the wellbore

Hydraulic Fracturing

• World-wide application– ~ 100,000 wells annually– 90% of gas wells– 70% of oil wells

• Predominantly used for low-permeability reservoirs– High permeability applications increasing

• Complex operation– Requires knowledge and high competence in a number

of areas of engineering and science

Fracturing Fluids• Functions:

– Transmit hydraulic pressure to fracture– Transport proppant into the fracture

• Desired Characteristics– Non-hazardous, environmentally benign– Compatible with reservoir– Low wellbore friction pressure– Control leak-off to the formation– Transport & suspend proppant until closure– Non-damaging to fracture conductivity

6

Fracturing Systems & Trends• Aqueous

– Slickwater– Linear polymer-viscosified fluids– Crosslinked polymer gels– Viscoelastic surfactant gels

• Non-aqueous – Gelled oil– Nitrogen gas– Emulsions– Gelled methanol

Slick Water

Linear Gels

Crosslinked Gels

VES

Non-Aqueous Fluids

% of worldwide fracturing treatments BJ Services Company, 2009 7

Aqueous Systems

• Strong transition to slickwater and low viscosity, non-crosslinked fluids driven by the increased development of ultra-low permeability reservoirs (from 21% to >50% of N. American treatments)

Crosslinked Gels

Linear GelsSlick Water

Slick Water

Linear GelsCrosslinked Gels

1998

2009

8

% of US Fracturing treatments

Slickwater

• Water with acrylamide polymers

– PAA polymers reduce pipe friction

– Minimal polymer loading with low system costs

– Low viscosity

– Poor fluid efficiency, proppant transport

– Minimal fracture damage potential9

Complex Network Fracturing • Slickwater is the preferred fluid for naturally fractured shale reservoirs (ultra low perm.)

• Massive volume of low viscosity fluids facilitates development of a large and complex fracture network

• Poor proppant transport and suspension capabilities typically necessitate high injection rates

Guar Polymer Systems

– Cost effective, used widely in food stuffs and cosmetics

– May be processed to enhance fluid properties in harsh environments

– Improved guar products yield much lower insoluble residues and higher viscosity per unit

11

• Guar is the most commonly used gelling agent for viscosifying fracturing fluids

-- Naturally occurring polymer extracted from guar seeds

Guar pods, seeds, splits, and powderModern Fracturing (2007)

Crosslinked Polymer Systems• Crosslinking a polymer exponentially increases

the fluid viscosity– 10 to 60 cP increased to 100 to > 1000 cP

• Crosslinking : – Increases treating friction – Improves fluid efficiency (leak-off control)– Improves proppant transport– Increases gel damage potential

Crosslinked Gel Vortex Closure, progression over 3 minutes, Modern Fracturing (2007) 12

Guar Polymer Systems

High viscosityShear stableGood proppant transport Good retained conductivity

Zirconium-X-linked20 – 60 pptg CMHPGBHSTs to 375oFpH 4 -10

Borate-X-linked 20 – 50 pptg GuarBHSTs to 300oFpH 9 – 12

Moderate viscosityShear sensitiveGood proppant transport Fair retained conductivity

Linear Guar10 – 20 pptgBHSTs to 200oFpH 6-8

Low viscosityShear stablePoor proppant transport Best retained conductivity

Modern Fracturing (2007) 13

Gelled Aqueous Systems

• Linear gel usage increased, mostly due to unconventional reservoirs applications in lieu of slickwater

• Crosslinked, high viscosity guar systems using low polymer loadings replaced up to 65% of previous crosslinked guar system usage

• Viscoelastic surfactant gels (VES), usage increased to 4% of non-slickwater, gelled aqueous fluids

Crosslinked Gels

Linear Gels

Linear Gels

Conv. X-linked

Gels

VES

Low Loading X-linked Gels

1998

2008

14

Low Guar Crosslinked Fluids

• High viscosity yield per unit of polymer• Provides for up to 50%

polymer loading reduction• Lower friction pressure

• Reduced loading results in less gel damage

• Higher regained conductivity

• Improved fluid recovery and cleanup• Lower Flow Initiation Stress (FIS)

15

• Viscoelastic surfactants used to gel fluids– No polymers

• Operationally simple

• Components multi-functional– No need for biocide, buffer,

clay control, etc.

• Poor leakoff control

• Good transport

• Non-damaging• Recovered fluids recyclable

Viscoelastic Surfactant Fluids

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• High Density Fracturing Fluids• Bottomhole treating pressures > 15,000 psi• Crosslinked guar in high density brine• Reduces surface treating pressure & HHP

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@ 20,000 ft, 12.5 ppg brine provides for a 4,300 psi reduction in treating pressure

Emerging Fluid Technologies

• Ultra High Temperature Systems:

• BHSTs from 350oF – > 500oF• Synthetic polymer-based• Stable > 2 hrs at 450oF

• Provides for execution of job sized sufficiently for proper stimulation without the requirement of a “cool-down” pad

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Emerging Fluid Technologies

Emerging Fluid Technologies• Ultra-high Quality Foams

– +/- 95 Quality foam (N2 , CO2 , or mixed gas)

– Favorable environmental impact characteristics • Minimized impact on water supply• Foamers chemically benign

– Most applicable for low-pressured reservoirs• Additional gas volumes enhance recovery

– Non-damaging, 100% regained conductivity

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• Associative Thickener Systems– Non-polymer gelled fluid

• Relies on ionic ‘association’ of additives• Attributes similar to VES systems

– Thickening initiated by elevated temperature,• Viscosity begins to increase at 150oF • Rheologically stable to >250oF

– Non-damaging• 100% regained conductivity

– Environmentally benign

Emerging Fluid Technologies

Emerging Fluid Technologies• Environmentally Acceptable Chemistries

– Governmentally driven• Most active in US & Europe• Growing activities globally

– In US, applies to all frac appls

– Replacement characteristics• Performance functionality• Safe to handle• Low toxicity• Biodegradable

21

TargetedMaterials

Diesel & BTEXBacteriacidesClay controlSurfactantsNon-emulsifiersCorrosion inhibitors

Proppants

Ottawa Frac Sand

Low Density Ceramic

Brown Frac Sand

• Proper placement creates a conductive pathway from the reservoir to the wellbore

• Proppant is the only material which is intended to remain in the reservoir after a hydraulic fracturing treatment completion and cleanup

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Proppant Characteristics• Transportability

– particle density, size, shape – fluid velocity, viscosity, density

• Particle strength @ in-situ stresses– particle composition, size, shape

• Fracture conductivity – particle concentration, size, packing

23

Proppant Usage Trends

010,00020,00030,00040,00050,00060,00070,00080,00090,000

100,000110,000120,000130,000140,000150,000160,000170,000180,000190,000200,000

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Tons

White Sand Brown Sand Resin/Ceramics/Speciality Total

Data courtesy of BJ Services Company USA

1999 - 2009: 660% increase in proppant usage

2002 – 2008: Sand has increased from 70% to 85% of total

Proppant Size Usage Trends

010,00020,00030,00040,00050,00060,00070,00080,00090,000

100,000110,000120,000130,000140,000150,000160,000170,000

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Tons

White 20/40 White 16/30White 12/20 White 30/50White 40/70 & 30/70 White 100 MeshWhite 20/50 Total

1999 - 2009: 20/40 reduced from >90% to <50% of total usage

2004 - 2008: 30/50, 40/70, & 70/140 usage increased > 1,000%

Data courtesy of BJ Services Company USA

Proppant ConductivityConductivity (Cf = kf w) is a measure of the

fracture’s ability to transmit fluids

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• kf = fracture permeability• w = fracture width• k = reservoir permeability • Xf = fracture length

f

fFD kX

wkC

Cf D contrasts the transmissibility of the propped fracture to that of adjacent reservoir

Fracture Conductivity• A key design parameter for successful

stimulation

• Subject to change over the life of the well due to:– Proppant particle failure– Effective stress increase with production – Damage: gel residuals, embedment, fines– Non-Darcy or multiphase flow

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Proppant Selection

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Most typically based upon propped fracture conductivity at reservoir closure pressure

• Higher proppant concentrations generally provide greater conductivities due to the increased imparted width. The exception is partial proppant

monolayers

• Strong industry trend driven by increased unconventional resource development to use of smaller diameter proppants at low concentrations

Fracture Conductivity

29

30

Effect of Proppant Concentration

Modern Fracturing (2007)

Effect of Proppant Size

31Modern Fracturing (2007)

(Penny (Stim-Lab), 1992)

Fracture conductivity damage from crosslinked gelled fracturing fluids with breakers typically ranges from 20 - 90%

Residual Fluid Damage

32

Gel Damage Regained Conductivity vs. Breaker Concentration

0

10

20

30

40

50

60

70

80

90

100

% R

egai

ned

Con

duct

ivity

VES, 2%

Slickwater

B/HE Guar, 25 ppg

Linear Guar,

40#

Zr/CMG, 2

0 pptg

B/Guar, 40 pptg

Zr/CMHPG, 3

0 pptg

No Breaker Low Breaker Moderate Breaker High Breaker

33Data courtesy of Stim-Lab Consortia

• Reduced density proppants (ultra-lightweight) to improve proppant transport and placement for enhanced conductive fracture area.

Emerging Proppant Technologies

34

0 50 100

150

200

250

300

350

Transport Distance, ft.

Bauxite, 3.50, 40/70 Sand, 2.65, 40/70 LWC, 2.55, 40/70Sand, 2.65, 70/140 ULWP-1.06, 30/80

SPE

106312Elliptical Geom.(3:1), 0.25”

width, Injection Rate 

1 bbl/ft, 3 cp

Transport of ULW 1.05 ASG Proppant 14/40 mesh; 4 cP slick water

20 mesh Sand@ 1,000 psi

“Emerging” Proppant Technology

Partial monolayers exhibit open areas around and between particles increasing the conductivity of the propped fracture

36Adapted from SPE-1291-G, 1959

Conductivity vs. Closures Stress Proppant Packs vs. Partial Monolayer

100

1000

10000

1000 2000 3000 4000 5000 6000Closure Stress (psi)

Con

duct

ivity

(md-

ft)

ULW-1.05, 0.02 ppsf 20/40 Sand @ 2.0 ppsf 20/40 Sand @ 1.0 ppsf20/40 Sand @ 0.5 ppsf 40/80 LWC @ 0.5 ppsf

37SPE-119385

• Stronger, more thermally stable, ultra-lightweight proppants to improve transport and conductivity

– First generation: 200oF / 5,000 psi– Current generation: 240oF / 7,000 psi– Next generation: 275oF / 8,000 psi

Emerging Proppant Technologies

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• Proppants with improved ability to mitigate non-Darcy flow issues common to high rate and/or multi-phase production

• Materials to mitigate effects of proppant pack diagenesis (scaling)

Emerging Proppant Technologies

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Emerging Fracturing Technology• Production Assurance

– Particulates containing controlled-release additives deployed in fracturing treatments for long-term flow assurance via inhibition of scale, salt, paraffin, or asphaltene deposition

– Reside within proppant pack and slowly release production chemicals to maintain the conductivity of proppant packs and to prolong the time to needed intervention (> 3 years protection experienced)

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• Ultra-high strength proppants for deep well applications (+20 kpsi)

• High strength proppants with reduced abrasive properties to protect hardware in high rate, low viscosity fluid applications

Emerging Proppant Technologies

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• “Smart” proppant to allow mapping of conductive fractures

– Live or activatable particles dispersed within proppant pack

– Once placed, can be located within reservoir for identification of the conductive fracture geometry and azimuth.

• Fracture width can be estimated from frequency

Emerging Proppant Technology

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Summary

• Hydraulic fracturing of unconventional reservoirs has resulted in significant shifts in the fracturing materials employed, most significantly to lower viscosity fluids and smaller proppant size.

47

Summary• Evolution of fracturing materials is ongoing

to effectively satisfy the developing needs of unconventional resources stimulation

• Innovation of fracturing materials is occurring to effectively fracture in the ever- increasing extremes of reservoir thermal and stress

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Hydraulic Fracturing Materials: Application Trends & Considerations

Harold D. BrannonBJ Services Company

Society of Petroleum Engineers Distinguished Lecturer Programwww.spe.org/dl

49

Thank You !

Questions ???