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Introduction to Fracturing

Objectives, concepts and main concerns

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Well Stimulation

Stimulation is a chemical or mechanical method of increasing flow

capacity to a well. Wellbore Clean-up: Fluids not injected into formation

Chemical Treatment

Perf Wash Matrix Stimulation: Injection below frac pressure

Matrix Acidizing

Chemical Treatment Fracturing Injection above frac pressure

Acid Frac

Propped Frac

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Applications for hydraulic fracturing

Low natural permeability

Natural production below economic potential

Skin By-Pass or higher permeability and soft formations.

Fracture for Sand Control

The injected fluid is pumped at a rate above the fracture

pressure of the reservoir to create cracks or fractures within the

rock itself.

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Propped frac & Acid frac

open fracture

during job

fracture tends to closeonce the pressure has been

released

sand used toprop the

frac open

acid etched frac walls

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Acid frac

Bottom hole pressure above fracturing pressure

Acid reacts with the formation

Fracture is etched

Formation must retain integrity without fracture collapse

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Hydraulic fracturing

Creates Deep Penetrating Fractures to :

Improve productivity

Interconnect formation permeability

Improve ultimate recovery By-passes damage

Increase injectivity

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Objectives of well fracturing

Maximize the NPV on well drilling and completion investment

Increase hydrocarbon production rate Increase the reservoir economical life

Increase reserves

Reduce, or overcome, near wellbore damage

Stimulation for reservoir management

Efficient drainage of laminated formations Delaying the onset of water production

Sand control

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Post stimulation production increase

0

100

200

300

400

500

600

0 20 40 60 80 100

Time (months)

BOPD

Well Economic Limit

Pre-stimulationproduction

Post-stimulationproduction

Well Stimulation

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Radial Flow

Close to the well velocity

increases Higher velocity generates

higher pressure drop

This high pressure dropdestabilizes the formation

(collapse, sand production, fines

production, scales, etc)

P1P1

P1

P1

P2

P2P2

P2

P3

P3P3

Pwf

Pr

Pr

Pr

Pr

Pr

>>>

>

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Frac objectives (high permeability)

Linear Flow

Bypass damage Increase wellbore connectivity

Minimize stress effect

Reduce velocities, minimizing

fines movement

damaged zone

bi-linear flow path

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Frac objectives (low permeabilities)

Increase production or injectivity by creating an high conductivity

channel Improve communication of fluids between the well and the

reservoir.

with Pr= Cst increase of the rate Q with Q = Cst produces/injects with lowerP.

Q

P

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Effect of the fracture

Pr

(Pwf)damage

(Pwf)frac

The reduction in drawdown is

a very important effect onproduction: less velocity near

the wellbore, less erosion,

higher Pwfs.

Tendencies for scaling and

sludge precipitation are

reduced.

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Modification of reservoir flow

Linear Flow: Early times andfor infinite conductivity fractures

Bi-linear Flow: Finite conductivityfractures

Pseudo-radial Flow: Long time

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Applications of Hydraulic fracturing

Connect discontinuous hydrocarbon bearing formations

production from lenticular formations Connect naturally fissured system

Assure production from laminated intervals Hydraulic fracturing forsand control

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Connecting lenticular reservoirs

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Natural fissured systems

Sub - Parallel Fissures

Orthogonal Fissures

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Laminated formations

Ensure wellbore connectivity with all producing intervals

Pay stimulated byan acid treatment

Pay stimulated bya fracture treatment

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Fracturing for sand control

Pressure

Distance

Reduced drawdown in formationsand production

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Harsh fracturing environments

Very high permeability ( 1-2 Darcy )

Weak barriers to fracture height growth

Very high pore pressure (i.e. overpressurized reservoirs)

Formations with a high degree of natural fissures Proximity to oil-water contact

Lenticular formations bounded by higher stressed formations

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Typical fracturing formations

Very tight formations => mD permeability

Wells with significant damage

Good producing wells (high permeability formations)

Fracture for Sand Control

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Equivalent wellbore

rw

rw

sww err ='

For example,

rw = 0.4 fts = -3

rw = 8 ft

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Non-dimensional fracture conductivity

F

PCD

Xk

wkF =

Expresses the influence of the fracture on the well conductivity

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FCD and equivalent wellbore

Low Permeability

High Permeability

0.01

0.10

1.00

0.1 1 10 100 1000FCD

rw'/xf

High Permeabilitykf w limited

Low Permeabilityxf limitedr

xw

f'

2

rk w

kw

f' .0 28

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Nolte-Smith plot

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Linear gel and crosslinking gel

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Fines and impurities