Aditivos de Cementacion

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Aditivos de CementacionAceleradores y RetardadoresModifican el Tiempo de FraguadoAlteran el desarrollo de la resistencia a la compresionExtendedoresReducen la densidad de la lechadaAumentan el rendimientoAgentes de PesoAumentan la densidadDispersantesMejoran la mezclabilidadReducen las presiones por friccion

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Aditivos para Perdida de FiltradoMateriales para Perdidas de CirculacionAditivos Especiales:Aditivos antiespumante/desespumantesEstabilidad del cementoAditivos ExpansivosAditivos para la migracion de gasAditivos gelificantesAditivos espumantesAditivos de Cementacion

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TSL-4274

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Tiempo de FraguadoControl paraPermitir finalizar el tratamientoEvitar que fluidos indeseados fluyan (gas)Reducir el tiempo de espera por el fraguado del cemento (WOC - reducir tiempo de taladro)Afectado porTemperaturaPresionTipo de Cemento (clase y granulometria)Mezcla y metodos de colocacionAceleradores y RetardadoresOtros aditivos (sal, dispersantes, aditivos para perdida de filtrado)

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AceleradoresProposito Reducir el tiempo de espera por resistencia compresiva (WOC)AplicacionesRevestidores someros (conductor, superficial)Condiciones de baja temperaturaEfectos retardantes de otros aditivosAditivosCloruro de Calcio (CaCl2) - 1-4%Cloruro de Sodio (NaCl) -

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Resistencia a la Compresion

Resistencia a la Compresion a diferentes Temperaturas

(psi)

60oF

80oF

100oF

CaCl2

(%)

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

1780

2

125

480

1510

410

1020

2510

1110

2370

3950

4

125

650

1570

545

1245

2890

1320

2560

4450

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Cloruro de Calcio (CaCl2)S1, S2, D77Acelerador mas efectivoRango 1-4%Afecta el Tiempo de Fraguado

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Efecto Secundarios del CaCl2Aumenta la temperaturaCalor de solucion del CaCl2Efecto adicional de aceleracion (en superficie)Expansion del revestidorAumenta la reologia (gelificacion)Probable aumento de la permeabilidadDisminuye la resistencia a los sulfatos

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Resistencia de Sistemas Salinos

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Cloruro de Sodio (NaCl)Cloruro de Sodio (D44) como acelerador Actua como acelerador < 15% BWOW Rango preferido 3 - 5 % BWOW

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Aditivos DeepCEM Dos componentes liquidos :Dispersante No-Retardante (D185)Acelerador (Set Enhancer D186)

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Aditivos DeepCEM : AplicacionesMedios de Aguas frias/bajas temperaturas (40F - 130F )Usado para controlar los riesgos de flujos de agua o gas superficiales(D500 GASBLOK* LT adicional)Usado en combinacion con el sistema DeepCRETE* para aplicaciones de baja densidad y bajas temperaturasUsado cuando son necesarios tiempos de transicion cortos, (ejemp. Rapido desarrollo de geles), rapido desarrollo de resistencia compresiva o es necesario alcanzar el fraguado en angulo recto a bajas temperaturas

Tiempo de Fraguado y Resistencia a la Compresion Efecto de la concentracion del D186(BHST=55F, BHCT=65 F)

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RetardadoresProposito permitir suficiente tiempo para colocar la lechada AplicacionesRevestidores Intermedios y de ProduccionRevestidores Superficiales y Conductores (tiempos de bombeo muy largos)Forzamientos y Tapones de CementoAlta TemperaturaClases de Retardadores QumicosLignosulfonatosD013, D081, D800, D801Acidos HidroxicarboxilicosD110Componentes InorgnicosD093, D074Retardadores mezcladosD028, D150, D121Disenados segun propositoD177, D161 & D197

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RetardadoresXXXXXXXXXXXXD13/D81D13/D81 con DispersanteD800/D801D800/D801 con D093/L10D110D110 con D93/L10D28/D150D28/D150 con D121D28/D150 con D93D161 UNISET HT (B178 solido)D177 UNISET LT (B155 solido)D197 AccuSETBHCT oFRetardador100 200 300 400 140100185125250250310300175300375220300350300400300450250100Fresh Sea 37% NaClXXXXXXXXXXXX

XX

XXXX

18%80250100250

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UNISET* D177 Retardador de Baja Temperatura hasta 105oC (220oF)D161 Retardador de Alta Temperatura desde 93oC (200oF)Rapido Desarrollo de la Resistencia a la CompresionNo afecta la rata de hidratacionMas tolerante a Errores de Concentracion y Temperatura Efectivos en agua fresca o agua de mar Sinergia cuando se usa en conjunto con aditivos UNIFLAC* Equivalentes Solidos (B155 LT, B178 HT)* Mark of Schlumberger

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UNISET* AplicacionesCementacion de Liners y Revestidores Operaciones en Una Etapa vs. Dos EtapasReemplazo de lechadas ligeras y principales por una sola lechada Forzamientos Tapones de DesvioAplicaciones de Coiled Tubing * Mark of Schlumberger

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UNISET* HT - Caracteristicas* Mark of Schlumberger

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UNISET* HT CS y TT Dyckerhoff Red Label a 16.0 ppg* Mark of Schlumberger

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UNISET* LT Sensibilidad a Concentracion 0246810Tiempo de Fraguado (hours)0.05 (140)0.15 (185)0.30 (220)Concentracion en gal/sk (Temperatura en deg F)Conc - 10%ConcConc +10%* Mark of Schlumberger

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Control de Perdidas de CirculacionReducir DensidadReducir presiones de friccionAgregar particulas de LCMGranularesEscamas/LaminaresFibrosas

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Reducir la Densidad de la Lechada

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Extendedores

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Materiales Granulares para Perdidas de CirculacionD42 - KOLITE* Carbon TrituradoSG - 1.3Concentracion - 5 - 25 lb/skClave: Estabilidad de la Lechada D24 - GilsonitaAsfalto Molido SG - 1.07Similar al D42Limitacion de Temperatura a 300oF MecanismoCrea PuentesDificultad al mezclarlo a altas concentraciones* Mark of Schlumberger

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Materiales en Escamas para Perdidas de CirculacionD29 (Escamas de Celofan)Concentracion - 1/8 a 1/2 lb/skD130 (Escamas de Poliester)Concentracion - 1/8 a 1/2 lb/skMecanismoForma una red en las zonas de perdidaManejo Dificultad al mezclarlo a altas concentraciones

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Fibras de CemNET CemNET* aditivo para perdidas de circulacionD95 hasta 300oF [150oC]D96 hasta 450oF [232oC]* Mark of Schlumberger

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DispersantesLa reologia de la Lechada es afectada por:Volumen de solidos / volumen totalInteraccion entre las particulas Reologia de la fase acuosa Se reduce con dispersantesPorque bajar la reologia de la lechada?Reducir las presiones de friccionMejoran la mezclabilidad de la lechadaReducir el agua para aumentar la densidad (hasta 2165 kg/m3 [18.0 lb/gal])Mejorar la eficiencia de los aditivos para perdida de filtrado

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Accin del Dispersante El Dispersante esta negativamente cargado, se fija en los Ca++La superficie del grano pasa a estar negativamente cargada Signos iguales se repelen Las particulas se dispersan Mas dispersante del necesario (sobredispersion) > Separacion de Fases

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DispersantesAditivos TIC* SulfonadosPNS - D65, D80, D604M, D604AMPMS - D145ANo retardantes (D185 DeepCEM*)Acidos y Sales OrganicasD121* Mark of Schlumberger

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Perdida de FiltradoDefinicinEs el Filtrado o fase acuosa, perdida hacia la formacinRevoque depositado sobre la superficie de la formacinPorque las lechadas pierden agua?Presin DiferencialMedio Permeable (formacion)Relacin Agua/cemento? HidratacinEtapas de la prdida de Fluido ( filtrado ):Prdida de filtrado dinmicaPrdida de fluido esttica

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Migracion de Gas a traves del revoque y cemento de baja calidadPuentes Anulares son ProbablesDano a las formaciones por el filtradoOtras propiedades:Efectos de la Perdida de Filtrado en las propiedades de la lechada

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Mecanismos del control de filtradoReduccion de la permeabilidad del enjarre en el cementoPartculas de material rellenando los porosPartculas de polmeros taponando los porosPelcula de polmero sobre la partculas del cemento/porosCambio en la distribucin de las partculas del cemento con dispersantesIncrementando la viscosidad de la fase acuosaAdicin de polmeros solubles al aguaEfectos pobres comparados con la reduccin de la permeabilidad

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Mecanismos

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Aditivos FLAC* ParticulasGel - D020, D152Latex- D600G (MT,M-HD,L), D700 (HT,HD,L)Microgel- D193 (AD,LT,L), D500 (AD,LT,L)Polimeros Solubles en AguaDerivados de Celulosa - D059 (MT,ND,S), D112 (MT,LD,S)UNIFLAC* - D167, D168 (solido/liquido todas las T)Aditivos SALTBOND* D065A, D080A, D604AM* Mark of Schlumberger

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Dispersantes con FLACsMecanismos de accin:Dispersan los granos de cemento, mejorando el empaque, reduciendo la permeabilidadFloculados con sal, accin de taponamentoSIN DISPERSANTECON DISPERSANTEREVOQUE EMPAQUE ALEATORIO

ALTA PERMEABILIDAD EMPAQUE ORDENADO BAJA PERMEABILIDAD

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Guia General (mL/30 min, API)Prevencion de migracion de gas30 a 50Liner< 50Revestidores de Produccion - Lechadas Ligeras< 250- Lechadas Principales< 150Rutina (si es requerido)-Lechadas Ligeras< 300- Lechadas Principales< 200Pozos Horizontales< 50Forzamientos disenados para la aplicacion

Cemento Neto La Perdida de Filtrado es: 1000 a 1500 mL/30 minControl de Filtrado

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Densidad de la Lechada Less WaterPesada Menos Agua Agentes de PesoDispersante Mas Altas Densidades

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Agentes de Peso

Sheet1

CODIGOAGENTESGAgua Adicional

gal/lb

D031Barita4.220.0240

D076Hematita4.950.0023

D907Cemento3.20.0529

D157(tetraoxido de Mn) Mn3O44.7 - 4.90.0011

Sheet2

Sheet3

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Retrogresin Por encima de 230 deg oF la temperatura esttica (BHST) desestabiliza el cemento, causando:Una reduccin en la resistencia compresivaUn Incremento en la permeabilidad Efecto causado por la conversin del gel C-S-H CSH gel ---------> alfa - hidrato silicato dicalcico amorfocristalinoFuerte, impermeabledebil, permeableC/S = 1.5C/S = 2.0Se previene agregando de 30 a 40% BWOC de silica, reduciendo la relacin C/S del gel C-S-H CSH gel + silica ---------> Tobermorita C/S = 0.8Tobermorita ---------> Xonolita + Gyrolita C/S + 1.0 C/S + 0.8Considerar las temperaturas de inyeccion o produccion

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Retrogresion

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Arena de Silica D030 y Harina de Silica D066

Sheet1

PROPIEDADD030 - Arena de SilicaD066 Harina de Silica

Tamano de Particula70 - 200>200

US Mesh

Agua Adicional~10%+12%

1.12 gal/sk1.34 gal/sk

Gravedad Especifica2.632.63

Aplicaciones

Alta DensidadPreferidaAlternativa

Baja DensidadAlternativaPreferida

SedimentacinAlternativaPreferida

MezclabilidadPreferidaAlternativa

Por encima de 300deg FAlternativaPreferida

Sheet2

Sheet3

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Aditivos AntisedimentantesLos aditivos antisedimentantes reducen:El Agua LibreLa SedimentacinLa Inestabilidad de las LechadasSon compatibles con todos los productos de cementacinSolo afectan la reologa de la lechadaRango de Temperatura : hasta 300 deg FAgente Antisedimentante:D153: 0.1 - 1.5 % BWOCAntisedimentante Lquido: D162: 0.005 - 0.025 gal/sk

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Estabilidad de la LechadaAgua LibreAgua Libre y Sedimentacion

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Agentes AntiespumantesProposito Prevenir la espumaPara prevenir cavitacin en las bombas y bombear una densidad realMecanismo de accion:Cambia la tension superficial Reduce la pelicula y causa su rupturaTipos de agentes antiespumantesPoliglicol-Eter Solido : D46 (0.2 lb/sk) Liquido : D47 (0.05 gal/sk)Silicones Liquido : D144, D175 (0.01 - 0.02 gal/sk) Liquido : M045 (0.05 gal/sk)

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FlexSTONE - Expansion

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Cemento FlexSTONE D180, D181 FlexSTONE

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Cemento DuraSTONE DuraSTONE D187 Aditivo DuraSTONE

**These 2 slides show how additives are broken into 8 categories. This module will cover all but special cement systems. A few special additives will be discussed. Special cement systems will be covered in section.Over 100 additives for well cements are available, either in liquid or powder forms. The cement additives used today can be generally split into eight categories as shown on the overhead. They will be discussed in the following sections of this module.Cements are used at temperatures ranging from below freezing in permafrost zones to 700 F (350 C) in thermal recovery and geothermal wells. Pressures encountered can range to more than 30,000 psi in very deep wells. In addition to severe temperatures and pressures, well cements may be required to deal with weak or porous formations, corrosive fluids, and overpressured formation fluids.The use of cement additives which modify the behavior of a cement system allows successful slurry placement under most conditions, and with the majority of cements available today.******Accelerators are used to shorten the setting stages of the hydration process (Stages I and II) and to accelerate the hardness process (Stages III and IV). The hydration of the main cement phases are increased: gypsum is consumed faster; the formation of the ettringite is enhanced; the portlandite is precipitated earlier. There is also a change in the C-S-H structure: the permeability is increased; diffusion through the protective layer is enhanced.Inorganic salts are generally accelerators of Portland cement, the chlorides being the most well known and most efficient.The best and most efficient is calcium chloride in its solid form. S1 is 77% pure CaCl2. It is used in concentrations ranging from 1 to 4%BWOC. One precaution must be taken note of - when CaCl2 is added to water, it will heat up the water by up to 10 to 20 degrees F.Sodium chloride is another well known accelerator but below 10%BWOW after which it is neutral. D44 usually has weaker action as an accelerator.Seawater can be used as an accelerator as it contains up to 3% NaCl plus some MgCl2 as well as other chlorides. The consistency of the seawater must be taken into account when lab testing - especially near river mouths as the concentration of chlorides can vary very much.The liquid form of CaCl2 known as D77 is equivalent to 3.5 to 4.5 lbs of S1. It is rarely used for economic reasons.****As an accelerator, strengths are more important than thickening time. The graphs shows the relationship of cement strengths versus the salt concentration. Low concentrations accelerate the strength. Maximum acceleration occurs in the range of 5-10% (BWOW). Strength is decreased at concentrations above about 20%. At very high concentrations, strength may be severely retarded. At saturation (generally said to be 37.2% BWOW), there may be no strength for extended periods of time (note that graph stops at 30%).*Sodium chloride (D44) can be used as an accelerator but it is not as efficient as calcium chloride. It effects the thickening time and compressive strength development of Portland cement in different ways, depending on its concentration and the curing temperature - see overhead. Salt acts as an accelerator at concentrations up to 10% BWOW. At 18-20% BWOW it is essentially neutral, and thickening times are similar to those obtained with fresh water. Above this NaCl causes retardation.The optimum concentration for acceleration is between 3 - 5% BWOW.Seawater contains up to 25 g/L sodium chloride which results in acceleration. The presence of Mg ( 1.5 g/L) must also be taken into account - see next pages. It should be remembered that salt concentrations are quoted as %BWOW, by weight of mix water and not the more conventional BWOC. ****Retarders inhibit hydration and delay setting of cement thus allowing sufficient time for slurry placement in deep and hot wells, or those applications which require long working times. In addition to retarder additives which are added to cements, retarded cements are available. These contain lignins, gums, starches, etc.. which provide the retarding action. However, these may not be compatible with cement additives and the setting times may be difficult to control consistently. Hence the development of Class G and H cements which are not allowed to contain introduced materials. Cement setting times are originally controlled when the cement is manufactured; i.e.. by grinding to a particular particle size, controlling the composition and the cooling rate of the clinker. Additional retardation required has then to be done in the field using chemicals. The technology of retarders is well developed and several types are used depending on the range of temperature application. The main groups are shown on the overhead and are discussed later in detailWhy they work is something of an enigma, although several theories have been proposed. Both the chemical nature of the retarder and the cement phases (silicate or aluminate) must be considered.The details of the mechanisms of action are discussed in the next pages.Lignosulphonate derivatives are the most commonly used retarders, being primarily the sodium and calcium salts of lignosulphonic acids. These are polymers (MW = 20,000 - 30,000) derived from wood pulp. They are usually unrefined and contain various amounts of saccharide compounds. Refined lignins have a more predictable behavior and are less sensitive to changes in cement composition and concentration variations. The higher temperature range retarders (D800/D801) are similar to D013/D081 but the lignosulphonates have been treated to improve temperature stability.Pure lignosulphonates have little retarding power. The retarding effect is due to the presence of low molecular weight and complex structures of carbohydrates and aldonic acids. They are effective with all classes of Portland cements; their normal usage range is 0.1 - 1.5% BWOC.Their mechanism of action is a combination of the adsorption and nucleation theories. The C3S hydration kinetics are mainly affected, and to some extent that of the C3A also. Such retarders perform best with low C3A cements.Their effective temperature range can be extended when blended with retarder aids such as sodium borate. At the higher limits of their ranges, the D13/D081 and D800/801 series may cause gelation with some cements, and dispersants will be required. This will also tend to increase the thickening time. When D800/D801 are used with salt slurries it is important that the salt be added after the mix water has been prepared or the retarder will precipitate out. The hydroxycarboxylic acid group of retarders contain hydroxyl and carboxyl groups in their molecular structures. The main retarders in this family are the gluconate and glucoheptonate salts which offer a powerful retarding action. They can easily cause over-retardation at BHCTs less than 200F (93 C). The main retarders of this group are the water solution of gluconate salts, D109 and D110; the D110 is a 50% solution of D109 to give increased sensitivity. These are classified as high temperature retarders. D109 is presently in the process of being obsolete.Their retarding action is generally attributed to hydroxycarboxylic groups which are capable of strongly chelating a metal cation such as Ca2+. Stable rings are formed which partially adsorb onto hydrated cement particles and those complexes which remain in solution poison nucleation sites of hydration products.To provide retarders for well cements which are effective at higher temperatures (i.e.. higher than 220F (104C), it is necessary to use blends of the various retarder compounds. The most well known of these is the high temperature retarder D28. It is a blend of a lignin amine and a sodium organic salt (sugar derivative). These are easily identifiable in D28 as two different colored powders. Because it is a blend and such a strong retarder, care must be taken when using samples for lab testing as it may be impossible to get a consistent and representative sample. It is recommended that the two components be used separately when performing laboratory tests. A liquid form of D028 has been introduced, D150, where 0.25 %BWOC D028 is equivalent to 0.10 gal/sk D150.It works by the sugars and sugar acids scavenging or complexing Ca2+ ions from the cement interstitial water delaying setting. It also acts to poison hydration product nucleation sites.D121 is primarily a dispersant which has good retarding properties. It is a mixture of a lignosulphonate and a gluconate (a hydroxycarboxylic acid salt). It is widely used as a retarder at higher temperatures and as a retarder aid to improve the effectiveness of D028 in the temperature range 300 - 350F (149 - 177C).Borax, or sodium tetra decahydrate, (D93) is used primarily as a retarder aid and has the ability to extend the effective temperature range of most lignosulphonate retarders up to 600F (315C). Its disadvantage is that it will adversely effect fluid loss. Why it works is still unknown but it is thought that it stabilizes the retarders at the higher temperatures. Borax is an inorganic retarder.**D161 was extensively tested within the BHCT range shown, but 250F (121C) is not the lower limit at which D161 will retard. The lower temperature limit for D161 depends on whether fluid-loss control is required. At temperatures below 250F (121C), gelation is sometimes observed depending on the fluid-loss additive and the brand of cement. If fluid-loss control is not required, testing has shown D161 to be effective at BHCTs as low as 165F (74C).D161 can be used with D44 for cementing salt sections with high BHCTs.When D161 is used with D600 or D134, the upper temperature limit will depend on the brand of cement. In many cases better results are obtained using D121 rather than D080 as the dispersant at temperatures above 300F (149C).D161 is a chemically pure product, unlike retarders based on natural products e.g., lignosulfonates, which contain impurities that make the retardation less predictable. Because D161 is a precise blend of salts in solution, thickening times can be predicted with certainty.The final compressive strength of the set cement is not a function of the concentration of retarder. Thus for a given thickening time, the rate of hydration is not decreased by D161. Rapid compressive strength development means that WOC times are reduced. A 16-lbm/gal slurry at 350F (177C) BHCT with a thickening time of 7 hr will develop 500 psi of compressive strength within 5 hr after setting and 3000 psi within 18 hr of being pumped.Small variations in the estimated BHCT (20F) will not significantly change the thickening time or compressive strength development.Small addition errors (10%) will not significantly affect the thickening time.Excessive shear will not impair thickening time or compressive strength development.*Because compressive strength development using D161 is relatively insensitive to small (30F) variations in temperature, good compressive strength development at the top of a long column of cement can be obtained.In squeeze cementing applications, advantage can be taken of having an extended thickening time without an associated delay waiting for compressive strength development before cleaning out inside the casing.In coiled tubing applications, D161 can be used to advantage due to its relative insensitivity to shear and the ability to design slurries with long thickening times without adversely affecting early compressive strength development of the set cement.*****The first way to reduce the density of a slurry is to simply add more water. This is also the cheapest. The problem is that this extra water tends to separate and become free water which can cause channels within the matrix of the cement.There are two ways that this extra water can be used up or bound up in such a way that it is not free: 1) by adding some sort of absorbent material which will absorb the water, for example, bentonite, silicate gel; 2) by adding light weight material which are usually absorbent as well, for example, expanded perlite, pozzolans, etc..*Cement extenders reduce slurry density and lower hydrostatic and placement pressures during cementing operations. This helps prevent the breakdown of weak formations and loss of circulation. It may also allow the number of stages required to cement a well to be reduced. Greater economy is also achieved by the increased yield of the standard extended slurries, but this may not be true for certain extenders.The typical density ranges available for extended cements are shown on the overhead. The use of a particular extender depends on the type of job to be performed and the results in terms of set cement properties required. Decreasing the cement density will reduce compressive strength development and increase the permeability of the set cement. They are more susceptible to strength retrogression at high temperatures so as the temperature increases, the choice of extender becomes more limited. Extended slurries are primarily used as filler materials (lead slurries) but in some cases will be used to cover and isolate zones. They may be required because the formation fracture pressure is too low to support conventional weight cements. In such cases the more expensive extended slurries may be used to ensure that good mechanical properties are achieved. Thus, for the extenders shown on the overhead, even though the possible density range is large, the range over which the extender is actually used may be limited. Often more than one kind of extender is used in the same slurry and the density of the slurry can be reduced to below that obtained with just one extender. Key ideas: Extenders reduce cement density, increase yield and reduce cost. Choose extender to give required cement properties for the particular job depending on cost and logistics.****Well cements are highly concentrated suspensions of solid particles in water. The solids content can be as high as 70%, and as such, they will exhibit high rheological values. The rheology of cement slurries is related to:The solid volume fraction: the solids content is a direct function of the slurry density. The higher the density the greater the number of cement particles in a given volume and the higher the rheology. The less dispersed the solid particles and the greater the aggregate sizes, the higher the rheology. Inter-particle interactions: which depend primarily on the surface charge distribution, and also the number of particles and ionic species present in the system. The higher the concentration of solid particles, the greater the interactions between particles and the higher the rheology.The rheology of the aqueous phase: The interstitial fluid of a cement slurry is an aqueous solution of many ionic species and organic additives whose rheology will be different to that of water. The higher the viscosity of the base fluid, the higher the viscosity of the slurry. This has a little effect compared to the solid volume fraction.Cement dispersants are solutions of negatively charged polymer molecules which are attracted to the positively charged sites on the surfaces of hydrating cement grains. There, the original positive charge is reversed and the system becomes increasingly negatively charged as the concentration of dispersant is increased. The resulting repulsive charges break up the cement particle aggregates into individual particles, and the system is dispersed.This allows turbulence at lower pump rates, and the generation of less friction pressure at any given pump rate. They allow a reduction in the water content of a slurry while maintaining pumpability. This allows high density, reduced water slurries to be mixed without the addition of weighting agents. Cement slurries also have to be properly dispersed to allow fluid loss additives to work efficiently. Key ideas:Cement slurry rheology defined by:Yield point (Ty) force which causes slurry to flow (lbf/100ft2)Plastic viscosity, (PV) : force required to move slurry at a given velocity (cP)The harder it is for cement particles to be moved and be kept moving (increased number particles/total volume, higher inter-particle forces, etc..), the higher the rheologyDispersants act to reduce inter-particle reactions and improve their mobility so to decrease rheology. Ty and PV will thus be reduced *The rheology of a cement slurry is due to the formation of hydrates (C-S-H gel and ettringite) when the anhydrous cement powder is added to water. Both chemical and electrostatic interactions take place during the initial and induction stages of the hydration process. The hydrolysis of C-S-H gel results in a surface negatively charged with silicate hydrate ions. Free calcium cations (Ca++) in the aqueous phase are attracted to these negatively charged groups on the C-S-H gel surfaces and react with them inducing a positive charge. The Ca++ ions can react with negative groups on the same grain surface or on adjacent or different grain surfaces. The latter results in the bridging of the two grains due to their mutual attraction for the Ca2+ ion. This occurs due to the large cement surface area and the competition for Ca2+ ions between adsorption sites. The overall effect is that portions of cement grains will be positively charged and other portions negatively charged. There will be an interaction between the oppositely charged patches. If no bridging occurred, the cement grains would be uniformly positively charged leading to spontaneous dispersionThe degree of particle interaction will determine the rheology of the slurry. The yield value is related to the force required to break the interactive bonds between particles and then produce movement. Plastic viscosity is related to the mechanical friction between particles. To disperse a cement slurry then either the electrostatic interactions must be modified to promote repulsion of particles, or the slurry must be mechanically sheared. Key points Surface ionization of cement particles results in surfaces becoming oppositely chargedInter-particle attraction requires a force to overcome it The greater the attraction the higher the yield and viscosityAttractive forces changed by addition of dispersantsTo disperse a cement slurry, it is necessary to disrupt the particle aggregates either by shearing or by the addition of chemicals called dispersants. Both actions release a portion of the entrapped water in the aggregates effectively decreasing the volume of the dispersed phase and reducing the slurry viscosity.The electrostatic charged network existing on and between cement grain surfaces must be broken to obtain this dispersion.Dispersants contain negatively charged groups which when added to the slurry, adsorb onto the positively charged sites (Ca2+) on the cement grains and thus suppress charged particle inter-actions. The polyanion dispersant molecule brings several negative charges. The cement particles become uniformly negatively charged, repel one another, deflocculate and the slurry is dispersed. (The amount adsorbed varies with the concentration of the dispersant). As more dispersant is added, the surfaces become more and more negative and thus more dispersed; the yield point will consequently decrease. Optimum dispersant concentration is reached when all the positive adsorption sites are saturated. At this optimum level the homogeneity of the cement structure is improved and permeability and shrinkage is reduced.The cement hydration process would be impaired if polycations were added to achieve dispersion by interaction with the negatively charged sites. Key points :Dispersant molecules are negatively chargedAttracted to positive sites on cement grains suppressing particle interactionsMore dispersant--> more negative sites --> more repulsionParticle aggregates deflocculated and slurry dispersed

*Several types of dispersants are used in the cement world. They are known as superplasticizers in the construction industry. 1. Sulphonates are the most common cement dispersants. These are solutions of highly branched polymer backbones. The most common are the polynaphthalene sulphonate (PNS) type dispersants, the dispersing ability of which is highly variable depending on the cement. D80 is typical of this family. Other sulphonates are the polymelamine (PMS) type. These are mainly used in the construction industry and in drilling fluids but are also effective in cement slurries. D145 is a typical example which was developed specially for microsilica cement systems as it has a much less retarding effect than D80/D65. 2. Lignosulphonates are mainly used as drilling mud thinners. They are also effective in cement slurries but will give extended thickening times. They are normally used as cement retarders (D13, D81, etc..). Their performance depends greatly on the cement quality and may cause gelation.3. Non-polymeric chemicals such as hydroxycarboxylic acids have strong dispersing properties and are also very strong retarders. Typical examples are D121 and D45 (citric acid). The trademark TIC is used for additives whose primary function is as a dispersant. Other additives can also be effective dispersants but their primary use is for other purposes. D65 and D80 are the most commonly used TIC dispersants. They are both PNS-type dispersants. D65 is totally soluble in water; D80 is a water solution (38%) of D65 and can be prepared by the addition of 1.0 lb D65 to 1.5 lbs fresh hot water (0.1% BWOC D65 = 0.03 gal/sk D80). They are compatible with most cementing additives and in salt solutions up to 18% BWOW NaCl. Since they are obtained from different sources, small variations in performance may be seen in the field. D121 is a high temperature dispersant (> 200F [93C] BHCT) with secondary properties of retardation and fluid loss control. It is recommended for use in reduced water systems with densities greater than 16.4 lb/gal. It is a very active dispersant and can also be used in salt cement systems. It is also an effective retarder aid when used with D028 and is also a good latex stabilizer.D604M is used for ETD cements where overdispersion would occur if D80 was used (in fresh water). D604M reduces free water development or sedimentation. It is compatible with most additives but when used with D109 retarder, free water may occur. (NB: D604 was replaced by D604M. They are the same chemicals but the chemical responsible for the formation of microgel has been changed to an environmentally safer product).D145 is a PMS dispersant which has a different mechanism of action to the other dispersants and only 20% active matter. It therefore does not affect the slurry thickening times. It degrades at temperatures above 180F which limits its applications. It is a useful dispersant for microsilica slurries.D80A and D604AM are used as dispersants/FLAC* additives in salt rich (above 18% BWOW NaCl) cement slurries, i.e... SALTBOND* cement. They are modified versions of D80 and D604M and give much better results than the previous D059/D045 salt FLAC/dispersant systems. Generally D80A is used for DTD cements and D604AM for ETD cements. A critical concentration is required to ensure good fluid loss. Most cements will work better with D604AM than D80A, even when DTD and then just the fluid loss needs to be checked.D45 was designed specifically for salt systems with over 18% BWOW NaCl where D65 caused gelation problems. It has a very strong retarding affect and calcium chloride should be used at temperatures below 140F. Care should be taken as false set and excessive viscosification may occur, even for large D45 concentrations. D45 is citric acid.

* Mark of Schlumberger*When a cement slurry is placed across a permeable formation under pressure, a filtration process occurs. The aqueous phase of the slurry escapes into the formation leaving cement particles behind in the annulus and forming a filter cake at the permeable formation face. This process is called fluid loss. Fluid loss is normally considered as a two-stage process, firstly the dynamic stage when the slurry is in motion and being placed in the well, and secondly, the static stage after placement (WOC or shutdowns during the job).To maintain adequate slurry performance, fluid-loss rates of 20 - 300 mL/30min are required. To reduce the fluid-loss rates of the 1,500 mL/30min normally obtained with neat slurries to acceptable levels, then fluid-loss control agents are added to cement systems. The higher the water-to-cement ratio of a cement slurry then the more likely will be fluid loss and acceptable criteria may have to be different to conventional slurry weights. Fluid loss increases almost linearly with temperature. At higher temperatures fluid loss is difficult to control and special additives must be used. Also the retarders required at such temperatures can interfere with, and damage fluid- loss control. Uncontrolled fluid loss may cause problems during or after the execution of a cementing job. If the fluid loss is high then:1. The slurry density may increase beyond an acceptable level during placement. This density increase may become very important when the area of the permeable formation is large and the contact time is long. Also, as the slurry density changes, so does its other properties (rheology, setting time, etc.).2. During static periods such as WOC, annular bridging may occur. This is a local process and is more likely to occur in a narrow annulus and/or restrictions. 3. Although the contact time of cement slurries compared to drilling fluids is short, damage to sensitive zones can occur if fluid loss control is not achieved. The filtrate has a high pH (12 - 12.5) and contains many ions (70% SO2-, 15% OH- and 12% Ca2+) which can be responsible for permeability impairment especially in shale and clay mineral formations. When water filters into a formation, some of the additive will do so too. It is thought that retarders and dispersants can be harmful. This may be a problem in fractured formations where the filtrate can enter deep into the formation. If the depth of invasion of the filtrate is short enough that perforations will extend beyond it, then no problems should be expected; this is normally the case.Cement particles do not endanger the formation permeability because even highly porous formations are able to retain enough particles to build a filter cake rapidly.Fluid loss affects all cement slurry properties. *The change in the water to cement ratio affects many properties of a cement slurry and the set cement. Fluid loss control is important to maintain the water to cement ratio as close as possible to that designed in the lab.The influence on thickening time and yield point is described in the next slide by the graph.Some formations can be damaged by the high pH filtrate.Gas migration could occur through the very highly permeable filter cake that is formed by a high fluid loss slurry as well as through the poorer quality set cement.The change in water to cement ratio is mainly due to the reduction in the water content of the slurry as filtrate to the permeable zone(s). Under dynamic conditions, when the filter cake does not grow, solid particles will remain in the moving slurry and thus increase the solid content. The slurry volume is therefore decreased and density increased (sometimes called slurry densification). This in turn affects hydrostatic pressure calculations and perhaps will require that an increased slurry volume be pumped to ensure coverage.Plastic viscosity and yield point increase, raising friction pressure and BHP. This may require a reduction in pump rates with the adverse consequence that turbulent flow will not be achieved and mud removal impaired. In principle the increase in solids content will improve settling tendencies and compressive strength. Bulk shrinkage is decreased by an order of magnitude.Some FLACs have a strong retarding effect on setting times. They adsorb onto cement grains and inhibit the cement hydration process. If fluid loss is not well controlled then the thickening time will be reduced due to a decrease in the water-to-cement ratio.Lead slurries will experience the highest fluid loss (they contain the most water, must deposit the filter cake, and will be exposed for a greater length and time to the formation). At first the solid fraction may not increase as filter cake is being deposited but once equilibrium is reached and the cake stops growing, then setting times may be affected as the solids content increases. This may increase the chances of annular bridging. These reasons are a strong argument for the use of fluid-loss additives in lead slurries.*The exact mechanisms by which fluid-loss control additives work are not fully understood but several processes are known to occur. Once fluid loss starts across a formation, a filter cake of cement solids is deposited on the formation surface. Fluid-loss additives decrease the filtration rate by:Increasing the viscosity of the aqueous phase which reduces the rate of filtration through the filter cake according to Darcies Law. This primarily applies to the water soluble polymer type fluid loss control agents but is not the main factor affecting fluid loss.Reducing the permeability of the filter cake. The fluid loss control additives work by blocking the pores of the cement filter cake thus sharply reducing its permeability. This can be due to either:mechanical blockage of pores by particulate materials (e.g.. bentonite and lattices), orblockage of pores by hydrated polymers which are adsorbed on filter cake particles. Above a minimum FLAC concentration the molecule chain concentration is sufficient to allow overlapping and interaction of chains. Therefore the blocking and plugging of pores is more efficient once the minimum concentration has been exceeded.Dispersion of the cement slurry improves fluid loss. Some fluid-loss control additives require that a dispersant be present in order for them to be effective and others have their efficiency much improved. Slurry deflocculation allows smaller cement particles to be formed while they are still in suspension and then when they are deposited in the filter cake they are packed closer thus reducing the permeability.Foams or emulsions are a special case and exhibit low fluid loss rates, the permeability reduction being due to a reduction in the relative permeability of water and the presence of 3 phases (solid, gas and water for foam).Two principle classes of fluid loss additives exist: finely divided particulate materials and water soluble polymers. Key ideas:Improve fluid loss control of slurries by:Increase viscosity of interstitial waterReduce permeability of cement cakeImprove ordering of moleculesFLAC additives required**The most commonly used classes of fluid loss control agents are from the family of cellulose derivatives.D8 was the first to be used (in the late 1950s). It is a slightly anionic carboxyethyl hydroxyethyl cellulose (CMHEC). It is primarily used as a cement retarder for special applications. It viscosifies interstitial water and its carboxyl groups adsorb onto cement grains blocking pores in the filter cake. The performance of such fluid loss additives in salt slurries is improved by the addition of a hydroxycarboxylic acid such as tartaric acid.D60, D59 and D112 are hydroxyethyl celluloses (HEC). They are basically the same but the D112 has a higher molecular weight thus allowing it to be used effectively for lower cement slurry densities. D59 is designed for use in salt water slurries and D112 can be used in both fresh and salt water systems. D60 is a mixture of D59 and the PNS dispersant D65 which is added to counteract the viscosifying effect of D59.FLAC properties are due to the viscosifying of the interstitial water and adsorption onto cement grains and blocking of pores by the molecule chains.All cellulosic fluid loss control additives share various disadvantages: a) they are effective water viscosifiers. At higher concentrations slurry mixability will be affected and ultimately undesirable viscosification of the slurry may result; b) up to 150oF (65oC), they are effective retarders so care must be taken to avoid over retardation of the slurry; c) their efficiency decreases with increasing temperature and they are not recommended for use above 235F (113C) BHCT; d) can create slurry foaming problems so higher than normal antifoam concentrations may be required. They will also foam when mixed in mix water.Dispersants are generally required to improve fluid loss control. Synthetic polymers are effective fluid loss control agents particularly for low temperature applications, i.e.. less than 130F (54C).D127 Low Temperature FLAC is used where the BHCT ranges from 80 - 130F (25 - 55 C). It has no retarding effect and is compatible with calcium chloride accelerated slurries. The calcium chloride will tend to thin the slurry whereas Superplasticizer -type dispersants are not effective and will thicken slurries. A critical minimum concentration of the additive is required to obtain good fluid loss control. There is a sharp threshold effect associated with this additive; within a very short concentration range (0.3 - 0.4% BWOC), the fluid loss rate falls from 500 to 20 mL/30min. The additive can produce unpredictable results and is really only effective when partially hydrated and stabilized so careful and consistent laboratory testing before use is required.Fluid loss control is achieved through adsorption of the polymer molecule chains on cement grains and the blocking of pores in the filter cake thus reducing its permeability.D603 liquid FLAC is effective in the temperature range 77 - 248F (25 - 120 C) BHCT in fresh and salt waters. It is important to optimize its concentration with respect to dispersant and is very sensitive to cement type and quality.D143 High Temperature FLAC is a high molecular weight polymer fluid loss control agent similar to D603 designed to give good mixability (low viscosity) at low temperatures. It gives good fluid loss control at temperatures above 180F (82C) up to 400F (205C) BHCT and in salt slurries with greater than 18% BWOW NaCl. The polymer structure is modified above 180oF (82C) and high pH due to partial hydrolysis. It is the partially hydrolyzed polymer which is responsible for giving the fluid loss control. Its liquid equivalent is D158 which is used in a concentration range of 0.2 to 1 gps. 0.7 gps is equivalent to 1% D143D73.1 liquid FLAC is a high molecular weight polyethyleneimine (50% active) polymer in water and is classified as a cationic fluid loss control agent. The polymer is effective over a molecular weight range of 10xE3 - 10xE6 and is highly branched. The higher the molecular weight, the more effective the fluid loss control. Intermingling of polymer chains in cement pores leads to a sharp decrease in free space and reduction in permeability.PNS-type dispersants (e.g.. D80 and D65) must be used to give significant fluid loss control. If used alone then D073 may give worse fluid loss control that just the neat cement due to a reduction in the filter cake permeability. With a dispersant an insoluble association is made between the two polymers and divalent cations in the slurry system to create particles which block cement filter cake pores reducing permeability.The main advantage is that such FLACs are effective at high temperatures, providing excellent fluid loss control up to 435F (224C). They also do not appreciably affect the thickening time or compressive strength. However, they tend to promote sedimentation due to the reaction with anionic particles/molecules also present in the cement system. Higher mass agglomerates are formed with a greater settling tendency. Obtaining an optimum slurry design can be difficult. They are most effective in fresh water and can be used in salt slurry systems with less than 15% BWOW NaCl but must be well dispersed in all mix waters.LT=Low temperature range - up to 130 FMT=medium temperature range - 130 to 230 FHT=high temperature range - over 230 FLD=low densities - less than 15 ppgND=normal densities - 15 to 16.5 ppgHD=high densities - over 16 ppgAD=any densities - 12.5 to 18 ppgL=liquid additiveS=solid additive*Cement slurries containing FLAC polymers must be well dispersed to obtain optimum fluid-loss control. Sulphonated aromatic polymers (D80, D65, D604M) or salt are almost always added in conjunction with FLACs.Deflocculation of the cement slurry is enhanced; the cement particles are smaller due to de--agglomeration, etc., and are also freer to move around. Thus packing of the cement grains in the filter cake and perhaps also the polymer aggregates, is improved. This leads to a reduction of the permeability of the filter cake. Care should be taken that over-dispersion does not result in settling and then give artificially improved fluid loss results when tested in the API test apparatus.Key ideas:Good high temperature FLACMust use with dispersant to be effective (forms complexes)*Fluid-Loss ControlFluid-loss control is required to:Maintain cement slurry properties while being placed in the annulus.Prevent cement dehydration which may cause bridging and excessive pump pressures, especially in narrow annuli across permeable formations.Reduce filtrate loss to permeable formations which can accelerate the loss of hydrostatic head.Minimize formation damage by cement filtrate.Fluid loss will be controlled to a great extent by the presence and quality of mud filter cake. In the presence of thin mudcakes of very low permeability, cement fluid loss will not be so great and higher loss rates are acceptable. However, good fluid-loss control is required (1) across permeable zones where fluid loss may be significant, (2) when gas migration is possible, or (3) for liners where annular gaps are restricted.Several kinds of cement additives are used to control fluid loss. They act to reduce the permeability of the cement filter cake and/or to increase the viscosity of the interstitial fluid. The designer must find the applicable FLAC* additive for the cement, water and other additives proposed.Fluid-loss tests are performed according to Section 10 of API RP 10B. This is a static test and is useful in as much that it allows comparisons of various slurries to be made. For such comparisons, be sure that the same differential pressure is used and quoted, in addition to the test temperature.

* Mark of Schlumberger

*To increase the density of the slurry, two methods can be used: 1) by adding heavier weight materials, for example hematite or barite; 2) or by adding more cement to the same quantity of water and by adding dispersant which will make the slurry more pumpable.*Two common weighting agents are:D076, Hematite: Its high SG makes hematite (iron oxide) an excellent weighting agent, It has a wide particle size distribution and slurry densities up to 22.0 lb/gal can be prepared. A minimum amount of additional water is required, 0.0023 gal/lb.D031, Barite: Barium sulphate has a SG of 4.33 but requires additional water to wet particles, i.e... 0.024 gal/lb. It is not as effective as D76 but slurries with densities up to 19.0 lb/gal can be prepared. Also, compressive strengths are decreased by the additional water.For lower density spacers, calcium carbonate (D151) is used as a weighting agent. The calcium carbonate is used to pre-weight the spacer to about 11.5 lb/gal and then barite or hematite can be used for heavier weights. This prevents too much settling when the particle concentration is not high enough.*When cement hydrates, the C3S and C2S clinker phases hydrate to form a quasi-amorphous gel of calcium silicate hydrate called C-S-H gel. Up to about 230 F (110 C), this gel is an excellent binding material responsible for the strength and dimensional stability of the set cement.However, at high temperatures, the C-S-H gel converts to alpha-dicalcium silicate hydrate. This new phase is highly crystalline and denser than the C-S-H gel, and as a result, shrinkage occurs thus damaging the integrity of the set cement and increasing its permeability. This phenomenon is termed strength retrogression. It not only occurs at depths where curing temperatures exceed 230 F. If the well producing temperature and flow rates are sufficient then the wellhead itself may exceed 230 F and therefore lead cement systems containing silica will also be required.Strength retrogression can be prevented by reducing the lime to silica (C/S) ratio in the C-S-H gel by the addition of fine silica flour or sand. This reduces the C/S ratio from 1.5 to 1.0 when 30 - 40 %BWOC silica is added to the cement system. At a C/S ratio of 1.0, a mineral known as tobermorite is formed which has low permeability and high strength, thus preserving the cement properties.Above 300 F (150 C), the tobermorite converts to xonotlite and a smaller amount of gyrolite. These are not so strong and impermeable as tobermorite but will preserve the integrity of the set cement at acceptable levels.Key points C/S Ratio of C-S-H Gel = 1.5C/S Ratio of Cement = 2.5 - 3.0C/S Ratio w/35% Silica = 0.83 - 1.0C/S Ratio of alpha-C2SH = 1.5 - 3.0*Strength Retrogression IIWhen the highly crystalline and dense alpha C2SH hydrate is formed, shrinkage occurs which effects the integrity of the set cement. Even though significant loss of compressive strength occurs, it is still sufficient to support casing.The real problem lies in the severe permeability increases. A neat cement with 0.02+ md permeability (after 3 days) at 290oF (143oC) may have 8.0+ md permeability (after 7 days) at 320oF (160oC). (The measurement of permeability is not done at downhole conditions and therefore its behavior may be quite different than shown. However, such testing for the long periods of time required would be difficult.)Reducing the bulk lime-to-silica ratio (C/S ratio) will prevent strength retrogression. The addition of 35 to 40% BWOC silica will cause the formation of tobermorite at temperatures above 230oF (110oC), and this will convert to other stable phase forms (xonotlite, etc.) at higher temperatures. These phases allow the set cement to maintain its integrity.At higher temperatures, the particle size of the silica will affect prevention of strength retrogression. At particle sizes exceeding 40 mm (D30), the strength and permeability will rapidly deteriorate after about 6 months. It is necessary to use D66 rather than D30 under these conditions. D66 has a particle size of approximately 10 mm. The formation of xonotlite is favored by the smaller particle size.Increasing the mix water ratio causes more strength retrogression. Up to 450oF (232oC), silicate extenders such as fly ash can be used with silica stabilized slurries. Above this temperature they should not be used as permeability increases and strength decreases in the long term (4 to 6 months). The deterioration will depend on the quality of the fly ash but it is best not to use any.*Two solid additives are commonly used to prevent strength retrogression. These are D30 silica sand and D66 silica flour. Their main properties and differences are detailed on the overhead.The D30 is coarser (average mesh size of 70 - 200) compared to > 200 mesh for D66. The particle size difference is mainly responsible in determining which silica is used for different applications.The smaller the particle size, then the greater the additional water requirement as the surface area to be wetted is larger. Less settling will occur with the smaller particles thus D66 is recommended for low density slurries and D30 for heavier, low-water slurries (less water required and settling is less of a problem). Rheological properties will be generally higher with a D66 slurry. Above 400 F (204 C), D66 is preferred as coarser silicas become less efficient at preventing strength retrogression.It is possible to use blends of D66 and D30 to optimize slurry properties.Key points : D30: Silica Sand (Coarse)D66: Silica Flour (Fine)Use 35 %BWOC dry-blended when BHST > 230 F*D153 is a solid additive - designed to control free water and sedimentation problems in unstable cement slurries form 12.5 ppg to 22 ppg.It does not have any significant compatibility problems with any other Dowell additivesIt can be dry-blended or prehydrated which is the preferred method for even mixing. It can be used with fresh or seawater - In seawater, prehydration takes longer and more D153 may be required.D153 has very little effect on other slurry properties except for the rheology, which it tends to increase the yield point. Fluid loss may appear to be decreased when D153 is added but this is due to there being a strong sedimentation tendancy before which would cause a layer of solids to be formed on the screen.Maximum temperature is 302 degrees F (150 degrees C).Concentrations range from 0.1% to 1.5%BWOC but are typical around 0.2 to 0.3% and may increase when more than 5%BWOW NaCl is used. Note that over 1%BWOC D153, severe foaming can occur which will not be controlled even by D144.Other methods of reducing the slurry instability are: increase the water to cement ratio (increase the density); optimize the slurry design by characterizing the type of cement (ETD or DTD), using the right type of dispersant, check for additive interactions, maintain a yield point around 5 lbf/100 ft2 or higher; using other viscosifiers, e.g. bentonite (0.5 to 1% in a 15.8 ppg slurry); ensure adequate mixing energy.**Antifoam agents are used with cement slurries to prevent excessive foaming problems during mixing which lead to pump cavitation and suction problems, and can cause slurries with erroneous densities to be pumped downhole.For an antifoam additive to be effective it must (i) be insoluble in the foaming fluid/slurry, and (ii) be more surface active than the foaming fluid. They produce a shift in the surface tension and/or alter the dispersability of solids so that the conditions required to produce a foam are no longer present. The insoluble antifoam acts by spreading on foam surfaces forming a film with a lower surface tension. The shock generated by the act of spreading is sufficient to cause foam destruction. The antifoam will also enter the foam and cause thinning of the foam's surface film due to gravitational drainage causing eventual rupture to occur.Two classes of antifoamer are used, (i) polyglycol ethers and (ii) silicones. Very small concentrations are required; usually less than 0.1% BWOC.D47 liquid, and D46 powder, antifoamers are of the polyglycol ether family. Powdered antifoamers such as D46 are usually high surface area, highly absorbent inorganic filler materials (e.g.. attapulgite) that have been treated with liquid antifoam materials. Both antifoamers are best when added to the system before water is mixed with the cement. When used with latex cement systems much higher concentrations of antifoam are required. (i.e.. up to five times more than normal in some cases), D47 should be well dispersed in the mix water to be effective, especially at low temperatures. They are not as effective as defoamers.D144 liquid is a silicone based antifoamer and defoamer. Such antifoamers are very effective in all cement systems and can be added to the system at any time to prevent either foaming or destroy foams which have already been formed. It is normally used for special cement systems with inherently bad foaming problems such as SALTBOND and latex cement systems.M045 is another silicone based liquid antifoam which is not as effective as D144 and will not break foams.Key ideas:Antifoam: Prevent foam before it starts (D47, D46, M45)Defoamer: Also destroy foam after it occurs (D144)Small concentrations requiredIncrease concentrations for latex and salt-based cement systems***