hydraulic fracturing in the hydrocarbon...
TRANSCRIPT
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Peter Fokker
Hydraulic fracturing in the hydrocarbon industry
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Outline
• Introduction
• Hydraulic fracturing – basics
• Types of applications
• Considerations of design
• Monitoring
• Concluding remarks
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Introduction
Stimulation of under-performing wells• Matrix acidizing
• Dissolve “skin” with acid (HCl, HF)• Not working with all kinds of damage• Concern of tubing corrosion
• Hydraulic fracturing• Increase inflow area• Pump fluid with high pressure – break the formation• Pump “proppant” in open fracture
• Keep frac open after shutin• High-permeability path from reservoir to well
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Hydraulic fracturing – Basic concepts
• Stress: maximum stress vertical; minimum and medium stresses horizontal
• Modes of fracturing
• Hydraulic fracturing: Tensile (mode I) – Vertical fracture has least resistance
σ1
σ3
σ2
Mode I: Opening Mode III: TearingMode II: Sliding
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Hydraulic fracturing – Visualization of the process
• Processes in hydraulic fracturing
Wellbore
Elastic opening
Pressure support of fracture walls
Friction
Leakoff
Fracture Propagation Rock Strength
Stress Intensity Factor
Injection
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Hydraulic fracturing – Concept
• KI: Stress intensity – measure of singular stress behaviourbeyond the tip
• Length increases when KI > KIc
• Volume balance
• Leakoff correlation
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Hydraulic fracturing – Complicating issues
• Profile of the minimum in-situ stress
• Elasticity profile
• Influence of pore pressure increase and temperature decrease on stress (poro-elasticity and thermo-elasticity)
• 3D pore pressure field complicates leakoff correlation
• Plugging of the fracture interior
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Layered Reservoir
• Stress Profile
• Elasticity Profile
• Permeability Profile
• Porosity Profile
dept
h
σ3
injection
log k
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dept
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injection
σ3 log k
Fracture vs time
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900
950
1000
1050
1100
1150
1200
1250
13000 2000 4000 6000 8000
Time (days)
Dep
th (m
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0
50
100
150
200
250
300
350
400
Frac
ture
leng
th (m
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= 0 MPa = 1 MPa = 2 MPa = 3 MPa
Example: Influence of a stress barrier
Fracture height
Fracture length ∆σ∆σ∆σ∆σ
Shale layer
Increased stress in shale layer
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Width and length contours (∆σ = 2 MPa)
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Hydraulic fracturing – Types of applications
Massive hydraulic fracturing• Large treatments• Low-permeability reservoir• Create additional contact area• Multiple fractures in a horizontal well
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Hydraulic fracturing – Types of applications
Tip-Screen-Out fracturing / Frac & Pack• Goal: Bypass damage• Typically in higher-permeability reservoir• Short fracture• Tip-Screen-Out to increase fracture width
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Hydraulic fracturing – Types of applications
Cracking
Fluid flow in Reservoir
Fluid flow in Fracture
Plugging and Channelling in Fracture
ReducedPermeability
Fracture
Water Injection under Fracturing Conditions
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Hydraulic fracturing – Types of applications
Barnett shale• Very low permeability• Naturally fractured
• Goal: interconnected fracture network
• Waterfracturing• Monitoring
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Design considerations
• The goal of hydraulic fracturing is economic
• Expected production• Analytic expressions (Prats)• Semi-analytic calculations• Reservoir simulation
• Connection with Geology• Flow barriers• Permeability• Heterogeneity• Natural fractures
• Dimensionless fracture conductivity
Optimum value:• High k: maximize width and
proppant permeability• Low k: maximize length• Proppant placement
Lkwk
C ffD ⋅
⋅=
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Design considerations
More input for design:• In-situ stresses• Fracturing pressures Minifrac test• Leakoff behaviour
• Effects of layering:• Containing capacity• Connection
• Natural fractures• Poro-elasticity• Thermo-elasticity
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Monitoring
Build up a knowledge base: • Treatment performance• Productivity monitoring
Treatment performance monitoring• Rates & Pressure traces
(e.g. Tip-Screen-Out)• Use fracture simulator• Tiltmeters
• Surface• Offset well
• Microseismic mappingtwo downhole receivers
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Monitoring
Build up a knowledge base: • Treatment performance• Productivity monitoring
Productivity monitoring• Well testing:
Effective fracture size• Productivity evaluation
e.g. Stimulated VolumeAnalysis
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Concluding remarks
• What is the goal?• Contact area• Bypass damage• Connect to natural fractures
• Design• Reservoir permeability• Fracture conductivity• Geology• Rock mechanics• Minifrac tests• Design software• Fluid selection• Proppant selection
• MonitoringBuild up a knowledge base
• Rates• Pressures• Temperatures• Tiltmeter mapping• Microseismics• Productivity