5/24/2018 A Intro to Fracturing Small
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Introduction to FracturingDuke Gray
August 26th, 2010
5/24/2018 A Intro to Fracturing Small
2/18
2006 Weatherford. All rights reserved.1
Objectives
Overview of fracturing Identify and explain porosity and permeability and how
they relate to fracturing
Identify the four principal parameters of fracturingdesign
Explain effective wellbore radius (rw)
Introduce general hydraulic fracturing materials
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2006 Weatherford. All rights reserved.2
Fracturing Overview
Hydraulic fracturing involves the injection of fluids into theformation at a rate and pressure above the fracture
pressure of the reservoir in order to create a fracture
within the rock itself. We then pack this space with
proppant which:
Improves productivity
Interconnects formation permeability
Improves EUR (Estimated Ultimate Recovery)
In the case of the Barnett Shale, the goal is to connect
the naturally fissured (fractured) portions with the
wellbore to bypass damage due to drilling and cementing
and to speed recovery of the hydrocarbons.
5/24/2018 A Intro to Fracturing Small
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2006 Weatherford. All rights reserved.
Propped Frac & Acid Frac
1/2"
open fracture
during job
(frac width = wf)
fracture tends to close
once the pressure has been
released
sand used to
prop the
frac open
acid etched frac
walls
5/24/2018 A Intro to Fracturing Small
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2006 Weatherford. All rights reserved.
P.E. Fitzgerald, The Value of Repeated Acid Treatments. Illinois State Geological
Survey, Urbana, 1934.
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2006 Weatherford. All rights reserved.5
Reservoir Rocks
Reservoir rocks need two properties to be successful:
Pore spaces able to retain hydrocarbon.
Permeability which allows the fluid to move.
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Permeability and Rocks
In formations with large grains,
the permeability is high and the
flow rate larger.
In a rock with small grains thepermeability is less and the flow
lower.
Grain size has a large effect on
permeability.
k
k
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Fissures (Fractures): Secondary Porosity
Fissures are caused when a rigid rock is strained beyond its
elastic limit.
The forces causing it to break are in a constant direction, hence all
the fissures are also aligned.
Fissures are an important source of permeability in low porosity
reservoirs (such as the Barnett).
Fissures
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Hydraulic Fracturing
Increase well productivity by creating a highly conductive path
compared to the reservoir permeability.
The fracture will extend through the damaged near wellbore area.
The fracture size is limited to two criteria : Drainage Radius
Cost
Damage
lxflxf= Fracture half length
Formation perm. = ke
Frac perm. = kf
wf
}
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Four Principal Parameters
Hydraulic fracturing does not change the permeability of the given
formation, but rather creates a permeable channel for reservoir fluids
to contact the wellbore.
The primary purpose of hydraulic fracturing is to increase the effective
wellbore areaby creating a fracture of given geometry, whose
conductivity is greater than the formation Dimensionless Conductivity
Where;
kf = fracture permeability
wf = fracture width
ke = formation permeability
lxf = fracture half length
xfe
ff
cd
lk
wkF
Fcdof 10-30 considered optimal
Fracture conductivity
-------------------------------
Formation conductivity
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Effective Wellbore Radius (rw)
By relating dimensionless fracture conductivity (FCD) to effective
wellbore radius (rw) and fracture length (lxf, or xf) a correlation canbe distinguished.
As shown here, the
Cinco-Ley Relation for rw,
as the ratio of rw/xf increases,
so does the dimensionless
fracture conductivity.
Fcd10-30
rw
= 0.5*lxf
In other words, the bit would
be as wide as the half length
of the fracture (effectively)!
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Effective Wellbore Radius (rw)
The expression (rw) is to equate the in-flow areas of wellbore and
propped fracture as illustrated. This relation shows for an infinitefracture, the effective wellbore radius (rw) is approximately fracture
penetration or length (lxf).
For a half length of 800 feet,
it would equate to a 800 foot
wide drill bit!
800 ft.
rw= 0.5*xf
rw= 0.5*800 ft
rw= 400 ftwidth = 800 ft!!!
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Hydraulic Fracturing Materials
Base Fluid Systems
Chemical Additives
Proppants
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Base Fluid Systems
Slickwater Applications
Low Friction
Low Viscosity (
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Chemical Additives
Gelling Agents
Friction Reducers
Crosslinker Control
pH Adjusting Agents
Clay Control
Breakers
Scale Inhibitors
Corrosion Inhibitors
Bactericide
Multiple varieties of all additives differing in concentrations,
ionic charges, limitations, and compatibilities
Oxygen Scavengers
Surfactants
Recovery Agents
Foaming Agents
Acids
Anti-Sludge Agents
Emulsifiers
Fluid Loss Agents
Resin Activator
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Proppant Permeability
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Proppants
Frac Sand (
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