HFSC

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Hydraulic Fracturing Short Course, Texas AM
University College Station 2005 Modeling,
Monitoring, Post-Job Evaluation, Improvements
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3D
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P3D and 3D Models

• FracPro (RES, Pinnacle Technologies)
• FracCADE (Dowell)
• Stimwin (Halliburton) and PredK (Stim-Lab)
• TerraFrac
• StimPlan
• MFrac

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Dimensionless Form of Nordgren Model
tD(xfD) inverse of xfD(tD)
xD 0 (wellbore)
xD xfD (tip)
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Propagation Criterion of the Nordgren Model

• Net pressure zero at tip
• Once the fluid reaches the location, it opens
  up immediately
• Propagation rate is determined by how fast the
  fluid can flow

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Other Propagation Criteria

• (Apparent) Fracture Toughness
• Dilatancy
• Statistical Fracture mechanics
• Continuum Damage mechanics

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Fracture Toughness Criterion
Stress Intensity Factor KI pnxf1/2
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CDM
What is the time needed for D to start at D 0
and grow to D 1 ?
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CDM Propagation Criterion
Combined Kachanov parameter
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P3D

• Pseudo 3 D Models Extension of Nordgrens
  differential model with height growth
• Height criterion
• Equilibrium height theory
• or Assymptotic approach to equilibrium
• Plus some tip effect

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3D (Finite Element Modeling)
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Fracture Toughness Criterion
Fluid flow in 2 D Fluid loss according to local
opening time Propagation Jumps Stress Intensity
Factor KI gt KIC ?
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Data Need for both P3D and 3D

• Layer data
• Permeability, porosity, pressure
• Youngs modulus, Poisson ratio, Fracture
  toughness
• Minimum stress
• Fluid data
• Proppant data
• Leakoff calculated from fluid and layer data

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Design Tuning Steps

• Step Rate test
• Minifrac (Datafrac, Calibration Test)
• Run design with obtained ?min (if needed) and
  leakoff coefficient
• Adjust pad
• Adjust proppant schedule

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Step rate test
Bottomhole pressure
Injection rate
Time
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Step rate test
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Fall-off (minifrac)
3 ISIP 4 Closure 5 Reopening 6 Forced closure 7
Pseudo steady state 8 Rebound
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5
2
3
4
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Injection rate
Bottomhole pressure
Injection rate
2nD injection cycle
1st injection cycle
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shut-in
flow-back
Time
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Pressure fall-off analysis(Nolte)
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g-function
dimensionless shut-in time
area-growth exponent
where Fa, b c z is the Hypergeometric
function, available in the form of tables and
computing algorithms
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g-function
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Pressure fall-off
Fracture stiffness
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Fracture Stiffness(reciprocal compliance)
Pa/m
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Shlyapobersky assumption

• No spurt-loss

bN
mN
Ae from intercept
pw
g0
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Nolte-Shlyapobersky
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1 g-function plot of pressure 2 get parameters
bN and mN
3 Calculate Rf (fracture extent -radius)
4 Calculate CLAPP (apparent leakoff coeff)
5 Calculate wL (leakoff width)
6 Calculate we (end-of pumping width)
7 Calculate h (fluid efficiency)
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Computer Exercise 3-1 Minifrac analysis
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Example

• Permeable (leakoff) thickness, ft, 42
• Plane strain modulus, E' (psi), 2.0E6
• Closure Pressure, psi, 5850

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Output
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From "apparent" to "real (radial)
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Redesign

• Run the design with new leakoff coefficient
• (That is why we do minifrac analysis)

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Monitoring

• Calculate proppant concentration at bottom
  (shift)
• Calculate bottomhole injection pressure, net
  pressure
• Calculate proppant in formation, proppant in well
• Later Add and synchronize gauge pressure

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Nolte-Smith plot
Wellbore screenout
Log net pressure
Tip screenout
Normal frac propagation
Unconfined height growth
Log injection time
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Post-Job Logging

• Tracer Log
• Temperature Log
• Production Log

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Available Techniques for Width and Height

• Measured Directly
• Formation Micro Scanner
• Borehole Televiewer
• Based on Inference
• Temperature Logging
• Isotopes (fluid, proppant)
• Seismic Methods, Noise Logging
• Tiltmeter techniques
• Spinner survey

Radius of penetration
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ScSb IrTracerlog
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Tiltmeter Results
after Economides at al. Petroleum Well
Construction
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Pressure Match with 3D Simulation
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3D Simulation
Texaco EP
FracCADE
OCS-G 10752 D-12
Actual
05-23-1997
Flow Capacity Profiles
Propped Width (ACL)
Conductivity - Kfw
Mark of Schlumberger
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Well Testing The quest for flow regimes
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Design Improvement in a Field Program

• Sizing
• Pad volume for generic design
• More aggressive or defensive proppant schedule
• Proppant change (resin coated, high strength
  etc.)
• Fluid system modification (crosslinked, foam)
• Proppant carrying capacity
• Leakoff
• Perforation strategy changes
• Forced closure, Resin coating, Fiber
  reinforcement, Deformable particle

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Example Tortuous Flow Path

• Analysis of the injection rate dependent element
  of the treating pressure
• Does proppant slug help?
• Does limited entry help?
• Does oriented perforation help?
• Extreme reconsidering well orientation
• e.g. S shaped

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Misalignment
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Fracture Orientation Perforation Strategy after
Dees J M, SPE 30342
From overbalanced perforation
From underbalanced perforation
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High Viscosity slugs
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Proppant Slugs
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Case Study Effect of Non-Darcy Flow

• Forcheimer Equation
• Cornell Katz

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Non-Darcy Flow

• Dimensionless Proppant Number is the most
  important parameter in UFD

Effective Proppant Pack Permeability
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Non-Darcy Flow

• Effective Permeability

keff is determined through an iterative
process Drawdown is needed to calculate velocity

• Reynolds Number

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Non-Darcy Flow Coefficient (b)

• Several equations have been developed mostly from
  lab measurements (empirical equations)
• General form of b equation
• where b is 1/m and k is md

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(No Transcript)
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Case Study Reynolds number
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Case Study Proppant number
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Case Study Max possible JD
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Case Study Optimum frac length
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Case Study Optimum frac width
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Summary

• Increasing role of evaluation
• Integration of reservoir engineering, production
  engineering and treatment information
• Cost matters
• Expensive 3D model does not substitute thinking
• Still what we want to do is increasing JD