Cement Additives and Mechanisms of action.ppt

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1

Cementing Additives and Mechanism

SPRINTOil & Gas Services

ObjectivesAt the end of this module, the will be

able to know the following:

•Explain why additives are added to the slurry

•List the families of cementing additives

•Explain the function of various cementing additives


Well Conditions

Temperature

Permeable formations

Mud RemovalFriction PressureMixabilityPumpability

Lost Circulation

Well ControlOver PressureWeak Formations

Strength Retrogression Antifoam

Gas control


Well ConditionsADDITIVE CATEGORY

SOLUTIONS

FLUID STABILITYFLUID LOSS CONTROL

HEAT RETROGRESSION HYDRATION PRODUCT SILICA

FOAMERS STABILIZED FOAM CAPABILITY

FOAMING AGENTS AND STABILIZERS

FOAM FOAMING TENDENCY ANTI-FOAM

ABNORMAL AND SPECIAL CONDITION

SLURRY PARAMETERPROBLEM

WELL CONTROLOVER PRESSUREWEAK FORMATION

DENSITY WEIGHTING AGENTSEXTENTERS

TEMPERATURE THICKENING TIME RETARDERSACCELERATORS

PERMEABLE FORMATIONS FLACMUD REMOVALFRICTION PRESSUREMIXABILITY/PUMPABILITY

RHEOLOGY GELLING AGENTSDISPERSANTS

LCMEXTENTERS

LOST CIRCULATIONPLUGGINGBRIDGING PROPERTIESDENSITY


Types of Cement Additives

o Accelerators and RetardersChange thickening timeAlter rate of compressive strength development

o ExtendersReduce slurry densityIncrease slurry yield

o Weighting AgentsIncrease density

o DispersantsImprove mixabilityReduce friction pressureReduce viscosityReduce water slurry

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Types of Cement Additives

o Fluid Loss Control-(Control the agues phase of the cement system to the formation)

o Lost Circulation Material-(to control the loss of the cement slurry to weak vagular formation

o Specialty: Antifoam/defoamer additives

Bonding agents

Expansive additives

Gas migration control additives

Gelling and suspending additives

Foaming additives SPRINTOil & Gas Services

Thickening /Setting Time

o Control to Reduce WOC (reduce rig-time)

Reduce chance for fluid/gas flow

Allow time to complete job

o Affected by Temperature

Pressure

Cement type (class and grind)

Mixing and placement methods

Accelerators and Retarders

Other additives (salt, dispersant, fluid loss additives) SPRINTOil & Gas Services

Conductor pipeo Prevents washing out under rig

o Short rig downtime

o Quick setting cement -rapid development of compressive strength

o Accelerated slurries, e.g.

Neat Cement+NaCl -- 3-5%

Neat Cement+CaCl2 -- 2-4%

Neat Cement+Sea Water

o Cemented with Stab-in or just driven


Accelerator

o Shorten hydration reaction stage I and II ( setting time)

o Accelerate stages III and IV ( hardening process )

o Change in C-S-H structure more permeable

o Offset retarding effects of other additivesI II III IV V


AccelaratorApplications

Shallow casings (conductor, surface)

Low temperature conditions

Offset retarding effects of other additives

Additives

Calcium Chloride (CaCl2) - 1-4% BWOC

Sodium Chloride (NaCl) - <15%

Other salts (carbonates, silicates, nitrates, etc..)

Organic chemicals (formats, oxalic acid, etc..)

Reduced water

Compressive Strength


Compressive Strength at Temperature(psi)

60oF 80oF 100oFCaCl2(%)

6 hr 12 hr 24 hr 6 hr 12 hr 24 hr 6 hr 12 hr 24 hr

0 NS 60 415 45 370 1260 370 840 17802 125 480 1510 410 1020 2510 1110 2370 39504 125 650 1570 545 1245 2890 1320 2560 4450

Calcium Chloride


oMost active acceleratoroRange 2-4%oPurity -77%oEffect on Thickening Time

Thickening Time (h:mn) CaCl2

(%BWOC) 91oF 103oF 113oF

0 4:00 3:30 2:32 2 1:17 1:11 1:10 4 1:15 1:02 0:58

Secondary Effects of CaCl2

o Increased temperature Heat of solution of CaCl2

Additional accelerating effect (on surface?) Casing expansion(thermal micro annulas)

o Increased rheology (gelation and increase PV and Ty)o Shrinkage (10-50%)o Possibility of uncontrolled setting ( flash set ) above

5 %o Possible permeability increase (after some time)o Reduce sulfate Resistance.


Compressive Strength of Salt Systems


Increase salt decrease CS

oEffect on Compressive strength developmentoPrefer range 3-5% BWOW

SaltFree

30%Salt

SaltwithFL

SALT-BOND

0500

10001500200025003000

SaltFree

30%Salt

SaltwithFL

SALT-BOND

Surface Casingo Unconsolidated zoneso Low temperatureso Deep water offshoreo Large volume of slurryo Light weight slurrieso 12.8 ppg Extended lead + 15.8 ppg neat tail

o Prehydrated bentonite 2-3%o Neat Cement+0.5-1% Nacl o 2/3 lead, 1/3 tail annulus height


Slurry Density

ChangingChangingofof

slurry densityslurry densityLighterLighter

More Water*•Absorbent(bentoni

te)•Light Material

Lower DensityLower Density

Neat Cement15.6 ppg Class A15.8 ppg Class G16.4 ppg Class H

HeavierHeavierLess Water

•Heavy Material•Dispersant

Higher DensityHigher Density

Lit fill is an exemption as an extender as a foamed cementSPRINTOil & Gas Services

Extenders

Classification :o Water based extenders

Water Increase free fluid Clays (Bentonite) check viscosity Chemical extenders (Sodium silicates)

need Ca2+ to worko Low density solids

• Pozzolans (Fly ashes, diatomaceous earth)• Microsilica

o Very low density materials Nitrogen Foamed Cement:- need stabilizer LITEFIL) Ceramic microspheres, 5000 psi max


Extenders

* Source CMM section 8

Bentonite D020

Gilsonite D024

LITEPOZ 3 D035

LITEPOZ 6 D048

KOLITE* D042

TXI Lightweight Cement D049

Sodium Metasilicate D079

Sodium Silicate D075

LITEFIL D124

Diatomaceus Earth D602

Foamed Cement 6

Microsilica

Extender or Lightweight System

14.7

14.7

15

15

14.5

14.6

14.2

15

9

11

11 15

15

14.5

12

12

12

11

11

11.5

12

12

12

14 15

Slurry Density ( lb / gal )

10 11 12 136 7 8 9


Bentonite Extenders

General properties•Water based extender•SG = 2.65•Dry blended or pre-hydrated•Concentration 0 - 20% BWOC

•Economical and widely available•Decrease compressive strength•Increase permeability•Viscosify slurries (lots of solids)

Bentonite ClaysBeneficiated(Peptized)

Non-treatedMontmorillonite

D020: Fresh waterAttapulgite: Sea Water


Sodium Silicates / Metasilicates • React with cation / Ca2+ Need CaCl2 • Form viscous, gelatinous silicate gel

binding extra water low free fluid separation

• Better than Bentonitic extender system : Low rheologies for mixing and turbulent flow Higher compressive strength

• No inherent fluid-loss control (use any FLAC)• Relatively low concentration• Ca-Silicate acts as accelerator at low temp ( < 185 F )• Thickening time defined by POD (Point of Departure) not 100 Bc


Low Density Solids

Pozzolans: • Natural Diatomaceous earth • Artificial LITEPOZ / Fly ash React with CaOH in slurry create cementicious material

Corrosion brine resistance Low permeability Thermal Resistance


Low Density Solids

Gilsonite• Solid hydrocarbon

( Asphaltite )• Inert ( no reaction )• Give good

compressive strength

• Max BHST 300 F ( melted )

• Can act as LCM • Bridge of at high

concentration and excessive water

Microsilica • Pozzolanic

material• Improve fluid loss

control• Increase BC• Max BHCT 185 F

( difficult to retard and gellation )


Very Low Density Materials

Ceramic Microsphere,LITEFIL

• Standard Pressure grade - 5000 psi

• Ceramic or glass microspheres

• Inert• Density range 8.5 -

14.5 lb/gal

Foamed Cement systems

• Nitrogen injected into slurry with foamer

• Very low densities achieved > 6 lb/gal

• Good mechanical properties


Intermediate Casings

o Workable sectionso 13 3/8” over 3000 feet deepo Often 2-stage cementingo Low costo Extended lead and neat tail, e.g.

Prehydrated bentonite 2-3 % 15.8 ppg tail

o All slurries to be retarded.o Can have some fluid loss control


Production Casings

o Isolate production zoneso Small diameter casingo Cost less importanto Good bondingo Usually has fluid loss

controlo Low friction pressureso Mud removal is importanto Slurry at 15.8 ppg or moreo All slurries to be retarded SPRINT

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Hydration of Cement

• I. PRE - INDUCTION PERIOD

• II. INDUCTION PERIOD

• III. ACCELERATION PERIOD

• IV. DECELERATION PERIOD

• V. DIFFUSION PERIOD

min hr

I II III IV V

days


Stages 1: Pre-InductionStage 2: Induction Period

SO4CaAl OH Ca Si

ETTRINGITE

C - S - H Gel

Seconds

Hours

Protective layers stops reactions - Pumping timeSPRINTOil & Gas Services

Hydration of Cement1-Preinduction period; Cement+ water Exothermic C-S-Gel i.e 2Ca3OSiO+H20 6Ca+ +10OH+2H3SiO4 Ca2(OH)2HSI2O7 (C.S.H Gel)+H2O 2- Induction Period: C.S.H Gel More ppt to C.S.H Gel Saturate CaOH3,4-Acceleration and Deceleration period: (Setting period) C3S+H2O Crystalyses (decrease porosity)5-Diffusion period: Decrease porosity and polymerization of CSH gel occur and

crystal change to C3H


Retardation of Cement System

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Purpose – to allow sufficient thickening time to place cementoApplications

Intermediate and production stringsHigh temperatureSurface and conductor casings (long pumping times)Squeeze and cement plugs

oChemical Classes of RetardersLignosulphonatesHydroxycarboxylic acidsInorganic compoundsBlended retardersDesigned for purpose

Mechanisms of Retardation

o Adsorption theory Adsorption of Retarder on to Cement Surfaces to Inhibit Contact with Water and Make the

Surfaces Hydrophobic

Modify CSH Gel to Make it Less Permeable

o Precipitation theory Ca and OH react with Retarder forming insoluble and Impermeable Layer around the

cement grain.

o Nucleation theory Retarder Adsorbs to Poison /stop Nucleation and Growth Sites

o Complexation theory Retarder Complexes with Ca to Minimise the Driving Force for Reaction and Prevent

Formation of Nucleation Sit


Properties of individual Retarderso Lignosulphonates (Low to Medium Temperatures)

Most Common Retarders Derived from Wood Pulp Active Ingredients Alcohols and Carbohydrates MW 20,000 to 30,000 Work Better with Low C3A which Consumes Retarder Work by Adsorption and Nucleation

o Carboxylic Acids (Medium to High Temperatures) Carboxyl and OH groups strongly Complex Calcium Work by Nucleation Powerful Retarders: Easily over-retard at T < 90oC Very sensitive to concentration


Properties of Individual Retarders

o Blended : Sugars plus Lignin Amine

1. High Temperature Applications2. Strongly Complexing 3. Works by Complextation and Nucleation Poisoning4. Can Separate Into Individual Components

1. D121: Mixed Dispersant and Retarder1. Lignosulphonate and HydroxyCarboxylic Acid2. High Temperature Applications often with D028

• Inorganic Retarders (Mid to High Temperature) Acid and salt thereof ( boric, phosphoric and chromic) NaCl >20% BWOW Oxides (zinc and lead)


Retarders Effects

• Possible negative effects of conventional retarders : Gelation (ex. Lignosulfonates) Dispersion Increased fluid loss Incompatibility Slow the development of compressive strength


Dispersants

o Cement slurry rheology Solid volume friction ( Volume of particles / total volume) because

70% solid particles in cement suspended in water. Particle interactions (Ty) Aqueous phase rheology

Change with dispersantso Why dispersants ?

Reduce viscosity and yield point Reduce friction pressures Improve cement slurry mixability Improve efficiency of fluid loss additives


Types of Dispersants

Sulfonates• Sodium Polynapthalene Sulfonate (PNS)• Polymelamine Sulfonate (PMS) liquid form• Aromatic polymer C200• Organic polymerLignosulfonates• Lignin Derivative/HydroxyCarboxylic Acid• Hydroxy Carboxylic Acid (Mix dispersant and retarder)


Selection of Dispersant

Based on :• Dispersibility behavior of cement

• ETD ( Easy to Disperse )• DTD ( Difficult to Disperse )• ETDS ( Easy to Disperse in Salt )• DTDS ( Difficult to Disperse in Salt )

• Bottom hole Circulating Temperature• Required slurry properties

Salt slurry

Fresh water slurry


Dispersant Action


•Dispersant is negatively charged, fixes on Ca++•Cement grain surfaces become uniformly negatively charged•Like signs repel – disperses particles•Too much dispersant (overdispersion) > Phase separation

Dispersant Action - Sterical

• Does not require a charged polymer• Adsorption of polymers able to induce ‘steric’ repulsion• Can be a dual effect with electrostatic repulsion (i.e.

PNS)• Has been shown to be a much stronger repulsive

mechanism

Cement grain

PNS

Dispersant molecule ‘adsorbs’ onto cement

grain surface


Fluid Loss in Cement Slurrieso Definition:

Filtrate (Agues solution) lost to the formation

Filter cake deposited at formation face

Cement particles left in annulus

o Why cement loses water: Differential pressure Permeable medium

(formation)o Fluid loss stages:

Dynamic Static SPRIN

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Effect of Fluid Loss


Gas migration through filter cake and poor quality cement Possible bridging Damage to some formations by filtrate Other properties:

Thickening Time versus Density

THICKENING TIME

YIELD STRESS

160

40 16.415.6

Thic

keni

ng T

ime

(min

)

Yiel

d S

tres

s

Slurry Density (ppg)


Increase density when losses decrease TT

Mechanisms of Fluid Loss Control

o Reduce cement filter cake permeability Particulate materials to fill voids Polymer particles to plug pores Change cement particle distribution with dispersants

o Increase viscosity of aqueous phase Water soluble polymers Small effect compared to permeability reduction


Mechanisms

Particle Plugging Polymer Plugging SPRINTOil & Gas Services

FLAC* Additives

o Particulate - Gel - Bentonite Latex - Anti Gas Migration Microgels - D193 (AD,LT,L)

o Water Soluble Polymers Cellulose Derivative –(Polypeptide) UNIFLAC* Additive -

o SALTBOND* Additives C200


Dispersant Effect on Fluid Loss


• Mechanism of action

FILTER Disperse cement grains and improve packing --> reduced permeability

CAKE

RANDOM PACKING

HIGH PERMEABILITY

ORDERED PACKING

LOW PERMEABILITY

With DispersantFilter Cake

Without Dispersant With dispersant

Fluid Loss Control


• inGeneral Guidelines• ml/30ml APIPrevent Gas Migration 30 to 5 mlProduction liners <50Production long String -Lead 200 -300 -Tail <150 ml

Routine if required - Lead <300 -Tail <200Horizontal well <50Neat Slurry 1000-1500ml/30 min

Weighting Agentso Requirements

High specific gravity Compatible particle size and distribution (settling) Low water adsorption (efficiency) Availability and acceptable cost Purity and consistency of product Inert

o Commonly used weighting agents Agent SG Additional water Barite 4.33 0.024 gal/lb

Hematite 4.95 0.0023 gal/lbMicroMax 4.80 0.0011 gal/lbCement 3.15

Carbonate --- ---(use for low density like spcare)


Strength Retrogression

• Define• At high temperature C-S-H gel is subject to

metamorphasis,which usually result in the decrease of compressive strength and increased permeability of set cement ,this phenomenon is called strength retrogression.


Strength RetrogressionAbove 230oF, cement undergoes:

Reduction in strength Increase in permeability

o Due to crystalline changes in CSH gelCSH gel ---------> alpha dicalcium silicate hydrateamorphous crystallinestrong, impermeable weak, permeable

o Prevented by addition of 30 - 40% BWOC silica (reduces C/S ratio of CSH gel)

CSH gel + silica ---------> Tobermorite

Tobermorite ---------> Xonotlite + Gyrolite

Care should be given to production temperatures




CaO:SiO2 Mole Ratio

Tem

pera

ture

(oC)

Ca0.SiO2 mole ratio

Temperature



Silica Sand & Silica Flour

Particle size US Mesh

Additional Water Specific gravity Applications: High density Low density Settling Problems Mixing Problems (Rheology) Use above 300°F

NAME SILICA SAND SILICA FLOUR70 - 200

±10% 1.12 gal/sk

2.63

Preferred

Alternative

Alternative

Preferred

Alternative

Alternative

Preferred

Preferred

Alternative

Preferred

> 200

+ 12% 1.34 gal/sk

2.63

Anti Settling Agent

o Controls free fluid and/or sedimentationo No significant effects on slurry properties,

except rheologyo Dry-blend or prehydrated (preferred), fresh or

sea watero Temperature range: less than 302oF (150oC)o Concentration: 0.05 to 2.0%BWOCo Must be used with dispersant


Slurry Stability

Free Fluid Free Fluid and Sedimentation SPRINTOil & Gas Services

Antifoam Agents

o Purpose – Prevent foaming Allow true slurry density to be mixed and

pumpedo Mechanism of action:

Changes surface tension Reduces film and causes rupture

o Types of antifoam agents --Polyglycol ethers (Neat slurry) Solid : (0.2 lb/sk) Liquid : (0.05 gal/sk) ---Silicones (GASBLOK Slurry) Liquid : (0.01 - 0.02 gal/sk)


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Cement Additives and Mechanisms of action.ppt

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