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SPE Distinguished Lecturer Program
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The SPE Foundation through member donations and a contribution from Offshore Europe
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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
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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
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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
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% 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
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• 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)
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• 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
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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
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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
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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
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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
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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.
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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
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Thank You !
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