5. CEMENTING

Habiburrohman, B.Eng, M.Eng. 1

Cement ManufactureDry Process

SILOS

PULVERIZERDRYER

OIL OR GAS

GYPSUM HOPPERS

PROPORTIONER

GRINDER UNIT

ROTARY KILNS

CLINKER COOLERS

CLINKER HOPPERS

GRINDINGMILLS

CEMENT SILOS

PACKAGING PLANT

STORAGE BIN

WASH MILL

CLAY

COAL

GYPSUM

CRUSHER

SILOS

LIMESTONE

2

Cement ManufactureWet Process

PULVERIZERDRYER

OIL OR GAS

GYPSUM HOPPERS

WET GRINDING MILLS

STORAGE BASINS

ROTARY KILNS CLINKER COOLERS

CLINKER HOPPERS

GRINDING MILLS

CEMENT SILOS PACKAGING PLANT

COAL

GYPSUM

CRUSHER

SILOS

LIMESTONE

CORRECTION BASINS

KILN FEEDERS

WATER

STORAGE BIN

WASH MILL

CLAY

3

Cement Hydration

4

Clinker Grain Structure

C3CS

C2S

C3A

C4AF

Silicates are approximately 80% of total material

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Principle Components of Portland Cement

• C3S Tricalcium silicate• C2S Dicalcium silicate• C3A Tricalcium aluminate• C4A Tetracalcium alumino ferrite

• C3S often used as model for cement hydration

• All phases have a role in sequence of hydration events and impact setting process

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Hydration Mechanisms

• Four Main Hydration Phases:

– WettingSHARP EXOTHERMIC PEAK; LASTS < 5 MINS

– InductionACTIVITY SEEMS LOW; CEMENT REMAINS FLUID

– SettingSUSTAINED EXOTHERMY; CEMENT THICKENS

– HardeningLOW HEAT FLUX; STRENGTH STILL INCREASING

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Heat Flow During HydrationH

eat

Flo

w%

Hyd

rati

on

of

Cem

ent

Time

Induction Period(Silicates Have Low Reactivity

During This Period)

Setting and Hardening

Diffusion40-50%

Hydrated Cement

Acceleration Deceleration

Pre-induction Period

(2%to 3% Hydration)

% Hydrated CementHeat Flow

min hours days

8

Hydration Mechanisms

• Two main theories of hydration process

– Protective Coating Theory

– Delayed Nucleation Theory

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Protective Coating Theory

• On contact with water, C3S AND C2S react to form calcium silicate hydrate (C-S-H) gel

• Initial surge or reactivity due to heat or hydration of free lime occurs

• C-S-H external reactions inhibited by semi-permeable gel coat, but internal reactions continue

• This is called the “dormant” or “induction” phases

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Cement Hydration (C3S)

MIXWATER

C3S

2 OH-Ca2+

H2O

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Cement Hydration (C3S)

MIXWATER

C3S

2 OH -Ca 2+

H2O

C-S-H - Gel

(Calcium Silicate Hydrate)

12

Protective Coating Theory

• Osmotic pressure within C-S-H builds due to internal reactions

• This causes C-S-H membrane to rupture

• Materials released include Ca(OH)2.

• Tubular growths of C-S-H (fibrils) form a network of interlocking with other hydration products

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Cement Hydration (C3S)

MIXWATER

C3SC-S-H - Gel

(Calcium Silicate Hydrate)

2 OH -

Ca 2+

H2O

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Delayed Nucleation Theory

• C3A enters into reaction with gypsum to form ettringite (calcium-sulpho-aluminate-hydrate)

• Ettringite coats C3A surface, reducing reaction until all gypsum present is consumed

• Ettringite then converts to calcium aluminate hydrates

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Cement Hydration (C3A)

MIXWATER

CaSO4

C3A

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Cement Hydration (C3A)

MIXWATER

CaSO4

C3ACASH

(Calcium Alumino

Sulphate Hydrate)

Ca 2+ + SO4 2-

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Thickening Time

• The viscosification that is observed from a consistometer test is the result of:– Interlocking effect of the hydration products– Consumption and immobilization of internal

water• The rate of viscosity build-up to final set is

influenced by:– Temperature– Additive chemistry

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Oilwell Cement

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Oil Well Cementing ?

• CEMENTING

• What is Oil Well Cementing ?

• Oil well cementing is a process of mixing a slurry of cement and water and pumping it through the casing pipe into the annulus between the casing pipe and the drilled hole.

• Cement plugs are also set in the wellbore to isolate zones e.g. loss zones, water bearing zones

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Oil Well Cementing

• Two general classifications of oil well cementing are :-

1. Primary Cementing

2. Secondary or remedial cementing

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OBJECTIVES OF CEMENTING• Primary Cementing

• Main objectives of primary cementing are :-

to support the casing pipe

to restrict the movement of formation fluids behind the casing

• Cement also provides the following advantages :-

seal off zones of lost circulation (fractured formation)

protect the casing from shock loads during drilling deeper section

protect casing from corrosion

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• Secondary Cementing

• Most common secondary cementing jobs are :-

Circulation squeeze

plug back cementing

squeeze cementing

OBJECTIVES OF CEMENTING (continued)

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OBJECTIVES OF CEMENTING (continued)• Secondary Cementing

• Circulation squeeze

• Cement slurry is circulated into the annulus through perforation, which are at the top and the other at the bottom of desired interval

• Reason for circulation squeeze are :-

supplementing a faulty primary job

extending the casing protection above the cement top

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• Secondary Cementing

• Plug back cementing

• Hole is plugged by cement in order to initiate a new drilling operation

• Plug back is carried out for a number of reasons:

Abandonment of the hole

Sidetracking the hole

Seal off lost circulation

Shutting off of water or gas encroachment

OBJECTIVES OF CEMENTING (continued)

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OBJECTIVE OF CEMENTING (continued)

• Secondary Cementing

• Squeeze Cementing

• Squeeze cementing involves forcing the cement slurry under pressure into open holes or channels behind the casing or into perforation tunnels.

• The operation is performed during drilling, completion and workover operations

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OBJECTIVE OF CEMENTING (continued)• Secondary Cementing

• Main purposes of squeeze cementing :-

• Supplementing a faulty primary cementing job

• Repairing casing defects

• Stopping lost circulation in open hole during drilling

• Shutting off old perforation for recompletion

• Reducing water cut in a producing well

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API Classification of Cements

• A wide range of the properties of the slurry (viscosity, density, and fluid loss) and the set cement (strength, permeability & porosity) are required to meet the down hole temperature & pressure and other conditions

• API provides specs covering eight classes of oil well cement designated as class A, B, C, D, E, F, G and H

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API Classification of Cements

• API Class A and B cements

Intended for use in wells from the surface to the depth of 6000 ft and 16 - 70 deg C

The recommended water to cement ratio according to API is 0.46 by weight (5.2 gal/sack or 19.71 ltr/sack)

• API Class C

Is a high strength cement and used for oil wells from surface to a depth of 6000 ft (16 - 77 deg C temperature)

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API Classification of Cements

• API Class D, E and F

As a basic and regarded as retarded cement

Intended for use from surface up to 16,000 ft depth

Premium cement because of high cost

Resistant to surface water

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API Classification of Cements

• API Class G and H

Regarded as basic cement; chemically similar to class B

Intended for use from surface up to 8000 ft depth

Can be modified by adding accelerator or retarder to suit wide range of depth and temperature

The recommended water to cement ratio according to API for class G cement is 44% (5 gal/sack or 18.9 ltr/sack) and class H cement is 38 % (4.3 gal/sack or 16.3 ltr/sack)

• The most common cement used in Malaysia is class G produced by Pan Malaysian Cement (PMC) in Pasir Gudang

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Cement Additives

• The of API cement above are used for wells with moderate bottom hole conditions

• It is necessary to modify cement properties to meet specific well conditions such as deep wells, HPHT, lost circulation zones, etc by adding chemicals

• The chemicals can be classified as follows :-

Accelerators – reduce thickening time

Retarders – increase thickening time

Fluid Loss reducers – control amount of fluid loss to formation

Weighting materials – increase/decrease density

Lost circulation materials – seal off lost circulation zone.

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Cement Additives

– Accelerator

• The accelerator is used to reduce the thickening time and set the cement faster by accelerating the hydration of chemical compound of cement.

• Liquid cement (known as cement slurry) will harden faster by adding accelerator

• Common Accelerators used are Sodium Chloride, Calcium Cholride and Calcium Sulphate (gypsum)

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Mechanism of Accelerators

MIXWATER

C3S

2 OH -Ca 2+

H2O

C-S-H - Gel

INCREASED

PERMEABILITY

2 Cl -

INCREASE RATE

OF OH- EFFLUX BY

COUNTER-DIFFUSION OF CL-

Hydrate morphology and ion flux

Mechanism of Accelerators

MIXWATER

CaS04

C3ACASH

PRECIPITATION

INCREASED

Ca 2+ + SO4 2-

pH LOWERED

SECONDARY

CaS04

Accelerated nucleation

Cement Additives

– Retarder

• The retarder will increase the thickening time or prolong the time of cement to set.

• It is necessary since more time is needed to place cement in deeper wells or to combat the thickening time reduction in high temperature environment

• Common retarder are saturated NaCl, lignosulfonate and its derivatives, cellulose derivative and sugar derivatives

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Mechanisms of Retarders

MIXWATER

+NET POSITIVE

CHARGE ON

CEMENT PARTICLE

2 OH - Ca 2+

H2O

LARGE ORGANIC MOLECULE

WITH NET NEGATIVE CHARGE

HINDERS MOVEMENT OF

IONS ETC. ACROSS

GEL MEMBRANE

SO3-

SO3-

SO3-

ADSORPTION AND STERIC HINDERANCE

PRECIPITATION THEORY

MIXWATER

CEMENT

GRAIN +

2 OH -Ca 2+

H2O

C-S-H - Gel

INSOLUBLE PRECIPITATE

HINDERS MOVEMENT OF

IONS ETC. ACROSS

GEL MEMBRANE

Mechanisms of RetardersMechanisms of Retarders

NUCLEATION THEORY

MIXWATER

CEMENT

GRAIN +

2 OH -Ca 2+

H2O

C-S-H - Gel

CRYSTAL GROWTH

POISONERS ATTACH TO

CRYSTAL GROWTH NUCLEI

AND PREVENT CRYSTAL

GROWTH

Mechanisms of Retarders

COMPLEXION THEORY

MIXWATER

CEMENT

GRAIN +

2 OH -Ca 2+

H2O

C-S-H - Gel

CHELATING AGENTS

SEQUESTER IMPORTANT

IONS FROM INTERSTITIAL

WATER AND CHANGE ION

BALANCE ACROSS GEL

MEMBRANE

Ca 2+

Ca 2+

Mechanisms of Retarders

Cement Additives

– Fluid Loss

• Fluid loss additives are used to control amount of liquid loss from cement slurries to the surrounding environment.

• These additives control the fluid loss by one of the following mechanisms :-

Increasing the particle size distribution of the slurry so that it holds or traps the liquid in it

Making the interstitial slurry water viscous which increased resistance to flow through porous formation

Forming an impermeable film or miscells within filter cake

Common fluid loss additives are organic polymers, dispersants and synthetic polymers

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Mechanisms of Fluid Loss Additives

MIXWATER

VISCOSIFICATION

OF MIXWATER

WALL BUILDING AND

PORE PLUGGING

ADSORPTION AND

RESTRICTION OF WATER

MOBILITY

SOLIDS PLUG

PORES AND BUILD MAT

ADSORPTION, PORE FILLING, WALL BUILDING

MULTIPHASE FLOW PHENOMENA

WALL BUILDING AND

PORE PLUGGING

MIXWATER

VISCOSIFICATION

OF MIXWATER

THE PRESENCE OF FOAMED

GASES CREATES MULTIPHASE

FLOW AND RESTRICTS FILTRATION

OF FLUIDS THROUGH THE

FILTER CAKE

Mechanisms of Fluid Loss Additives

Cement Additives

• Weighting Materials

• Most stable cement slurries have densities in range of 15.5 - 17.5 lb/gal.Weighting materials are used to increase the density of cement slurry depending on the requirement

• Weighting Reducing Materials

The weight of cement slurry can be reduced by :-

• Adding material that increases the water content such as clay and silicate materials

• Using light weight materials such as pozzolan, gilsonite or nitrogen

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Cement Additives

– Weighting Materials (continue)

• Light weight cement is used on weak formation or loss circulation zones

• The weight of cement slurries can be increased by adding barite, illmenite or hematite

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Cement Additives

– Lost Circulation Materials

• The lost circulation materials are used to combat cement lost into very permeable, cavernous or fractured formations

• The lost circulation materials prevent the loss of cement by one or more of the following mechanisms

Preventing fracture inducement by reducing hydrostatic pressure as in lightweight cement

Cure the lost circulation by forming a low permeability bridge across the permeable opening

• Common LCM can be classified as fibrous, granular and flakes

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Special Problems

• Strength Retrogression– Silica flour / sand prevents detrimental reactions at > 230 °F– Up to 210 °F : hydration products differ only in morphology and

microstructure– Above 210 °F: amorphous silicate hydrates form. Size range from x-ray

amorphous to highly crystaline– Above 230 °F: onset of retrogression, large crystals, low strength, high

permeability– Up to 300 °F : 35% silica sand or flour prevent formation of di-calcium

silicate hydrate (orthorhombic phase).– Above 300 °F: 35% silica flour as increased surface area required for

inhibition.

Special Problems

• Gas Migration Control– Agents that minimize slurry

depressurization or that decrease gas mobility in the cement paste (eg. by permeability reduction) during liquid to solid transition

• (BA-10, BA-29, BA-56, BA-58L, BA-86L, FL-45LS, FLAG-56, BA-100L, BJ BLUE)

Special Problems

• Lost Circulation– Agents which induce thixotropy can help prevent

or cure losses by reducing wellbore hydrostatic or by building high flow resistance in the fractures

• Microannuli/Poor Bonding– Agents which induce expansion after initial set, or

materials that impart adhesion or improve elastic modulus may help provide better isolation

Free Water Control Additives

• Under downhole conditions, it is important to control:– Free water– Slurry stability

• Problems– Zonal isolation– Collapsed casing (steam) in geothermal wells

• Applications– Horizontal, deviated and slimhole environments– Geothermal wells.

• Products– Impart strength to gel structure of cement

FWC-2, FWC-10, FWC-47, FWC-47L, BJ BLUE

Free Water Channels

Free water

Channel

Measured

Free Water

45°

Cement

Slurry

END

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