A Intro to Fracturing Small

5/24/2018 A Intro to Fracturing Small

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Introduction to FracturingDuke Gray

August 26th, 2010


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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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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.


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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


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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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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



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

}



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



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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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 (

A Intro to Fracturing Small

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