001 SG - Formation Damage

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Universidad Nacional de MedellínOctober 24-25, 2002


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Formation Damage

Types, Mechanisms & Prevention


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OUTLINE

• Definition of Formation Damage

• Types

• Classification• Influence of Geology-Rock Properties

• Operation Related Damages

– Drilling

– Completion

– Stimulation

– Production

– Workovers

• Summary


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FORMATION DAMAGE

“a reduction of permeability around awellbore, which is the consequence of drilling, completion, injection, stimulation,

or production of that well”*

* BP Well Productivity Awareness


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Productivity Potential. Skin Factor


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Skin Damage Factor

• It is identified at the beginning of well testing

• It is identified when pressure drops are recordedin addition to those corresponding to idea radial

flow

• Positive skin means high pressure drops near

wellbore, then productivity will be less in

comparison to another well with skin=0

• Negative skin means productivity is higher in

comparison with another well with skin =0


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Skin Damage Factor


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Flow Efficiency

• Skin is an useful mathematical concept, but it does notprovide a correct idea of damage effect on productionrate

• Fluid Efficiency is amore useful concept:

FE= Actual Production Rate( with skin) qr

IdeaI Production Rate ( without skin ) qi

FE = ln ( re/rw ) = 7

ln ( re/rw) + s 7 + s

Both production rates ( current skin and skin cero ) requireto be

measured under identical pressure drop conditions.


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Skin Damage Factor

• Damaged Well

? Ps>0, S>0, FE


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Productivity Index

• Measurement of production rate per each psi of

pressure drop.

TYPES OF FORMATION


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TYPES OF FORMATIONDAMAGE

• Physical Reduction in Pore / Pore Throat

Size

• Relative Permeability Reduction to

Hydrocarbons


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PHYSICAL REDUCTION IN PORESPACE

• Drilling Mud Solids and Filtrate Invasion

• Cement Filtrate Invasion

• Completion/Workover Solids and FluidsInvasion

• Perforation Damage Zone

• Plugging of Formation with Native Solids

• Asphaltene or Paraffin Precipitation

• Scale Precipitation in theFormation/Perforations

• Formation of Emulsion in the Formation

• Growth or Injection of Bacteria• Compaction of Reservoir with Production


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REDUCTION

• Water Coning

• Condensate Banking• Fluid Saturation Change and Fluid

Blocking• Wettability Change

• Emulsion Formation

• Relative Permeability Change

FORMATION DAMAGE CLASSIFICATION


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FORMATION DAMAGE CLASSIFICATIONBY PROCESS

Process

Type

Phy sical Pore Siz e

Reduction

Relative

Permeability

Reduction

F lu i d -Rock

I n t e r a c t i o n

• Fin es m igration

• Clay sw e l l ing

• Sol id s invasion

• Adsorption.precipitation

large m olecules

(polymeric)

• Wettabi l i ty chang e d ue

to adso rption of su rface

active com pou nd or

rem ov al of n ative

c o m p o u n d s

F l u i d - F l u i d

I n t e r a c t i o n

• Form ation s o f s cales ,Em uls ion and s lud ges

• Flu id satu ration chang eand f lu id b locking

Pressure/Temp Change

• S cale form ation• Wax/A sp haltene Form ation

• G as breakout• Conden sate banking

• Water conin g

M echani cal

Processes

• Stress ind uced p erm

change• Perfo ration p lu gg in g

-


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-TYPE

• Porosity, Permeability and Pore Structure

• Rock Type

– Sandstone

– Carbonate

• Cementation, Cleanliness, Heterogeneity• Clay Content

– Kaolinite (plate booklets prone to migrate)

– Illite (fibers prone to catch moving fines)

– Chloride (random platelets, often Fe rich)

– Smectite (prone to swell & block pore throats)


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ROCK

• CT Scanning/Core Photo

• Geological Description• Thin Section, SEM Description, XRD

• Ø Vs. K, Other Data From Conventional Core

Analysis• Pore (Hg Injection) and/or Particle Size

Distribution

• Capillary Pressure

• Relative Permeability


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Pore Level Characterization

FORMATION DAMAGE


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FORMATION DAMAGEDURING DRILLING

• Solids Usually Invades More Permeable Sections of

Reservoir , Can Reduce Permeability Dramatically.

• Mud Filtrate Invasion Can Cause Damage by– Swelling and dispersion of clays

– Scale precipitation

– Fluid saturation changes/blocking

– Chemical adsorption/retention and emulsion

• Natural Fractures Increase Well Productivity as longas they are not Blocked by Mud Invasion.

• Laboratory Tests Can be Utilized to Minimize

Formation Damage During Drilling


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COMPLETIONS

• Completion Types

– Well design (vertical, high-angle or horizontal)

– Completion design (Barefoot, uncementedliner, cased & perforated)

• Casing and Cement

• Completion Fluids

– Types

– Cleanliness, compatibility– Displacement

• Perforating (tunnel length, clean-up)

• Sand Control (Gravel packs, Frac-Pack,chemicals)


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STIMULATIONS• Reasons for Stimulation

– Very low native permeability

– To by-pass Near-wellbore damage• Acidization

• Hydraulic Fracturing

• Formation Damage During Acidization

– Corrosion and Iron Reprecipitation

– Fluid incompatibilities– Fines mobilization

– Liquid Blocking

– Cement Bond Destruction


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STIMULATIONS (cont.)

• Prevention of Damage During Acidization

– Perform acid compatibility tests with all fluids

to be used to eliminate potential problems

– Carry out core tests at the reservoir conditions

with actual rock and fluids to assess benefit

– On-site quality control on chemicals supplied

– Clean all pipework to be used

– Control wellhead pressure to prevent fractures– Throughout acid job, monitor and record all

parameters carefully to compare with the

expectations

STIMULATIONS ( t )


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STIMULATIONS (cont.)

• Prevention of Damage During Fracturing

– Perform compatibility tests with all fluids to be

used to eliminate potential problems– Carry out realistic tests with treating fluids to

determine breaking of crosslinked fluid

– On-site quality control on proppant andchemicals supplied and take frequent samples

– Clean all pipework to be used

– Throughout acid job, monitor and record all

parameters carefully to compare with the

expectations


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DAMAGE

• Precipitation

– Scale Precipitation (carbonate and sulfates)

– Asphaltenes– Waxes-very limited

• Fines Migration

• Phase Related Perm Reduction

– Condensate banking

– Water coning– Gas breakout

• Stress Induced Perm Changes

• Injection Well damage

FORMATION EVALUATION


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FORMATION EVALUATION

BASED ON FORMATION DAMAGE

IDENTIFICATION

ROCK FLUIDS RESERVOIR

MineralogicalInformation

(Drilling Cuttings)

X-Ray Diffraction

SEM

Petrographic Analysis

Rock Properties

( core samples)

Young’s ModulusPoisson’s Ratio

Sonic Logs

Permeability

Porosity

Formation Fluids

Characterization( fluid samples)

Oil Water

Paraffins,

Asphaltens

Bo

API

Viscosity

Physical &

Chemical

Analysis

Resistivity

PBU / DST Electrical Logs

Drainage

Radius

K.h

S

P*

Resistivity

Sonic

σmin

Density

Lithology

σmin

CBL,CAST-V

MRIL


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WORKOVERS

• An Operation Upon an Existing Well

• Types

– Scale treatment– Wax and asphaltene cleanout

– Recompletions (repair of existing design,

sidetracking, reperforation, etc),

– Stimulations (acid and fracturing).

– Water shut-off

– A combination of the above

• Follow Best Practices, Especially the ones

Worked Before

k


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Skin Damage Factor


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SUMMARY

• Know your Reservoir

• Be Aware of the Problems

• Apply/Develop Solutions to Prevent Damage

• Think in Terms of the Life of the Well, Not Very

Immediate Future• Communicate/Work with Others-Teamwork

• Employ Best Practices


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Data Adquisition TREATMENT SELECTIONTREATMENT SELECTION


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Data Adquisition

K= Logs, Well testing, Laboratory

Φ = Logs. Laboratory

σmax,

σmin = Logs, SRT, MinifracSw, So, Sw

Mineralogy

Litology = Logs , Drilling cuts, cores

Reservoir pressure

Flowing Pressure

Skin

Productivity

S>0 (+)

NO

YES

Reservoir Geology

Formation Fluids

Damage identification Depth Damage

Low K

Fines, Clay and

Carbonate content

NO

YES

YES

NO

Acidizing

Frac

TREATMENT SELECTION TREATMENT SELECTION

001 SG - Formation Damage

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