12. contaminacion.ppt

CONTAMINACIN Y TRATAMIENTO DEL FLUIDO DE PERFORACIN

IDENTIFICAREL CONTAMINANTE

DETERMINAR UN TRATAMIENTO

PRUEBA PILOTO PARA CONFIRMAR EL TRATAMIENTO

TRATAR EL CONTAMINANTE

Factores Que Afectan la Severidad de la ContaminacinTipo de sistema de lodo

Tipo de contaminante

Concentracin de contaminante

Tipo y concentracin de slidos

Contaminantes Qumicos ComunesCemento

Anhidrita/yeso

Magnesio

Sal

Gases cidos (CO2 y H2S)

CONTAMINACIN DE CEMENTO

Contaminacin de CementoCa(OH)2 Ca2+ + 2(OH)-pH < 11,5pH > 11,5

Solubilidad del Hidrxido de Calcio vs. pH02040608010089101112pH% Solubilidad del Calcio

Contaminacin de CementoFuentesPerforacin del cemento

Barita contaminada

Contaminacin de CementoPropiedades Fsicas del LodoPeso del Lodo (MW)Sin cambioViscosidad Embudo (FV)AumentoVPSin cambio a aumento ligeroPCAumento importanteGel InicialAumento importanteGel a 10 min.AumentoPrdida de FiltradoAumentoSlidosSin cambio a aumento ligero

Contaminacin de CementoPropiedades Qumicas del LodopHAumentoPmAumentoPfAumentoMfAumentoCa2+Aumento si pH < 11,5Disminucin si pH > 11,5

Contaminacin de CementoTratamientoEliminar el cemento duro con equipos de remocin de slidos

Reducir el pH y las alcalinidades

Precipitar el ion calcio

Contaminacin de CementoTratamientoLignito reducir las alcalinidadesCa(OH)2 + 2RCO2H Ca2+ + 2RCO2- + 2H2O(cido Orgnico)Bicarbonato precipitar el calcioCa2+ + NaHCO3 Na+ + H+ + CaCO3

Contaminacin de CementoTratamientoSAPP -reducir las alcalinidadesprecipitar el calcio

Na2H2P2O7 + 2Ca(OH)2 2Na+ + 2H2O + Ca2P2O7

Contaminacin de CementoSistema de Poliacrilamida Parcialmente Hidrolizada (PHPA)

Contaminacin de CementoSistema de PHPA / TratamientoTratar inicialmente con 1/2 1 lbs/bbl de cido ctrico para reducir el pH a 7.

Tratar inicialmente con 1/4 1/2 lbs/bbl de bicarbonato de sodio

Contaminacin de CementoSistema de PHPA / TratamientoTratar el lodo contaminado por cemento en la lnea de flujo con 1/4 1/2 lbs/bbl de cido ctrico para controlar el pH a < 10,0.Aadir bicarbonato de sodio para eliminar el resto de la contaminacin de cemento mediante el tratamiento.No aadir polmeros al lodo hasta que se elimine el cemento mediante tratamiento y el pH se estabilice a < 10,0.

Contaminacin de CementoSistema de PHPA / Tratamientocido Ctrico reducir el pH

Contaminacin de CementoSistema de PHPA / TratamientoBicarbonato precipitar el calcio

Ca2+ + NaHCO3 Na+ + H+ + CaCO3

Contaminacin de CementoTratamientoTolerar:Diluir

Aadir lignosulfonato

Aadir aditivos de control de prdida de filtrado si es necesario

CONTAMINACIN DE ANHIDRITA/YESO

Contaminacin de Anhidrita / YesoAnhidritaCaSO4 Ca2+ + SO42-YesoCaSO4 2H2O Ca2+ + SO42- + 2H2O

Anhidrita / YesoFuenteFormacin

Anhidrita / YesoPropiedades Fsicas del LodoPeso del Lodo (MW)Sin cambioViscosidad Embudo (FV)AumentoVPSin cambio a aumento ligeroPCAumento Gel InicialAumento Gel a 10 min.AumentoPrdida de FiltradoAumentoSlidosSin cambio

Anhidrita / YesoPropiedades Qumicas del LodopHDisminucinPmDisminucin ligeraPfDisminucinMfDisminucinCa2+AumentoCl-Sin cambio

Anhidrita / YesoTratamientoPrecipitar el calcio

Aumentar las alcalinidades

Anhidrita / YesoTratamientoCarbonato de Sodio tratar el ion calcio

Ca2+ + SO42- + Na2CO3 2Na+ + SO42- + CaCO3

Aadir soda custica para aumentar las alcalinidades

Anhidrita / YesoToleranciaAumentar el pH a 9,5 10,5

Dilucin

Aadir lignosulfonato para desfloculacin

El CO2 de la formacin y de la atmsfera terminar precipitando el calcio

Solubilidad del Hidrxido de Calcio vs. pH02040608010089101112pH% Solubilidad de Calcio

Anhidrita / YesoToleranciaSi se anticipan grandes secciones de anhidrita, convertir a un sistema de lodo yeso

Anhidrita / YesoConversin del SistemaDiluirExceso de yeso (8 12 lbs/bbl)Soda custica (pH 9,5 10,5)Lignosulfonato para desfloculacinAgentes de control de prdida de Filtrado que toleran Ca2+ (si es necesario)

CONTAMINACIN DE MAGNESIO

Contaminacin de MagnesioFuenteAgua Salada

Formacin (sal carnalita)* * descrita en la Seccin sobre Sales

MagnesioTratamientoPrecipitar?

o Secuestrar?

MagnesioTratamientoPara Precipitar:

Aadir Carbonato de Sodio

Mg2+ + Na2CO3 2Na+ + MgCO3

MgCO3 es soluble

MagnesioTratamientoMg2+ + 2OH- Mg(OH)2 pH > 10,5pH < 10,5Para Secuestrar:

Aadir una fuente de hidroxilo

MagnesioTratamientoCALCa2+(OH-)Slo secuestra el magnesioSODA CUSTICANa+ OH-Secuestra el magnesio y el calcioPOTASA CUSTICA K+OH-Secuestra el magnesio y el calcio

MagnesioEfecto sobre el Rendimiento del LodoLas arcillas no se hidratan tanto en agua dura

Prdida de Filtrado ms difcil de reducir

Los productos no son tan solubles

CONTAMINACIN DE SAL

Contaminacin de SalFuentesSal de Roca

Agua de preparacin

Agua de la formacin

Tipos de Sal de RocaHalitaNaClSilvitaKClCarnalitaK MgCl3 6H2O

Sal(Disociacin)NaCl + H2O Na+ + Cl- + H2O

KCl + H2O K+ + Cl- + H2O

K MgCl3 6H2O + H2O K+ + Mg2+ + 3Cl- + 7H2O

Sal en Agua de la FormacinNa+K+Ca2+Mg2+Cl-

Contaminacin de SalPropiedades Fsicas del LodoPeso del Lodo (MW)Depende de la densidadViscosidad Embudo (FV)AumentoVPAumento (si gran concentracin de sal)PCAumento Gel InicialAumento Gel a 10 min.AumentoPrdida de FiltradoAumentoSlidosLa retorta indica un aumento

Contaminacin de SalPropiedades Qumicas del LodopHDisminucinPmDisminucinPfDisminucinMfDisminucinCa2+Aumento ligero a importante segn el tipo de salCl-Aumento

Contaminacin de SalOpciones para el TratamientoTolerar

Convertir a un lodo saturado de sal

Desplazar con lodo base aceite o sinttico

Contaminacin de SalToleranciaDiluir

Aadir Soda Custica para controlar el pH

Aadir lignosulfonato para controlar el PC

Aadir agente de control de prdida de filtrado (si es necesario)

Contaminacin de SalConversin/DesplazamientoConvertir el sistema de lodo a un sistema saturado de sal o desplazar con un sistema base aceite o sinttico

Conversin a un Sistema Saturado de Cloruro de SodioDiluir los slidos de baja gravedad especfica (LGS) (realizar una prueba piloto antes de la conversin si hay suficiente tiempo y las condiciones lo permiten)Aadir NaCl hasta el punto de saturacin (110 120 lbs/bbl)Aadir soda custica para mantener el pH al nivel deseadoAadir lignosulfonatoAadir agentes de control de prdida de filtrado

CONTAMINACIN DE CARBONATO / BICARBONATO

Carbonato / BicarbonatoFuentesAire (atmsfera) inyectado por las bombas, tolvas mezcladoras, zarandas y agitadoresIntrusin de gas CO2Sobretratamiento con carbonato de sodio o bicarbonatoDegradacin de ciertos aditivos del lodoMayora de la barita

Carbonato / BicarbonatoPropiedades Fsicas del LodoPeso del Lodo (MW)Sin cambioViscosidad Embudo (FV)Aumento ligeroVPSin cambioPCAumento ligeroGel InicialAumento ligeroGel a 10 min.AumentoPrdida de FiltradoAumento ligeroSlidosSin cambio

Carbonato / BicarbonatoIndicadoresReaccin mnima o ninguna reaccin a los desfloculantes qumicos

Una reduccin de las propiedades reolgicas puede producirse cuando se aade soda custica si el pH del lodo < 10,0 antes de aadir la soda custica

Carbonato / BicarbonatoEquilibrioPorcentaje

Punto Cedente vs. CO32- y HCO3-102030405060020406080100120140160180200PC (lb/100 pies)Milimoles / LitroCO32-HCO3-

Carbonato / BicarbonatoPropiedades Qumicas del LodopHDisminucinPmAumenta GeneralmentePfAumenta GeneralmenteMfAumentoCa2+DisminucinCl-Sin cambio

Efecto producido cuando se usa soda custica sola para aumentar el pH (sin alcalinidad debido a carbonatos o bicarbonatos):pHNaOH, lbs/bbl PfOH, ppm 90,000140,00050,17100,00140,0051,7110,0140,0517,0120,140,5170,0131,45,01.700,01414,050,017.000,0

OBSERVACIN: Cada vez que la concentracin de NaOH aumenta en un factor de 10, el pH aumenta en una unidad.

Prueba de Pm y Pf02040608010002468101214PorcentajepHPorcentaje de varias especies de carbonato a diferentes valores de pHCO3=H2CO3HCO3-Iones de Hidrgeno

Prueba de Mf02040608010002468101214PorcentajepHPorcentaje de varias especies de carbonato a diferentes valores de pHCO3=H2CO3HCO3-Iones de Hidrgeno

Mtodos para Determinar los CarbonatosMtodo de Pf / Mf

Mtodo de pH / Pf

Tren de Gas de Garrett

Mtodo de Pf / MfEl mtodo de Pf/Mf no es un mtodo cuantitativo para determinar la concentracin de ion carbonato/bicarbonato en el lodo.

Modificando las razones Pf/Mf se puede establecer tendencias, las cuales pueden ser usadas para determinar la probabilidad de carbonato/bicarbonato

Mtodo de Pf / MfSi Mf < 5,0 cc de 0,02N H2SO4, en general no hay ningn problema de carbonato

Si Mf > 5,0 cc y la razn Mf/Pf aumenta, ser necesario usar un mtodo de determinacin ms cuantitativo (pH/Pf o un Tren de Gas de Garrett)

Mtodo de pH/PfPara un anlisis cuantitativo de los carbonatos, es crtico usar un medidor de pH preciso.Medir y registrar a partir de la hoja de control de lodo: pH, Pf y fraccin de agua (Wf)Determinar a partir de los clculos: cantidad de CO32- y/o HCO3- (mg/l) presente en el lodo

Carbonato / BicarbonatoTratamiento02040608010002468101214PorcentajepHPorcentaje de varias especies de carbonato a diferentes valores de pHCO3=H2CO3HCO3-

Carbonato / BicarbonatoTratamientopH < 10Aadir calpH 10 > < 11 Aadir cal y yesopH > 11 Aadir yeso

Tren de Gas de Garrett

Carbonato / BicarbonatoSlidos vs. CarbonatosMuchas veces se considera que un problema de slidos es un problema de carbonatos. Ambos aumentan la viscosidad y los esfuerzos de gel del lodo, especialmente en la lnea de flujo.

El siguiente anlisis debera determinar si el problema resulta de la contaminacin de slidos o de carbonato / bicarbonato:

Slidos vs. CarbonatosAnlisisAnalizar los slidos del lodo.

Buscar tendencias que se han desarrollado durante los ltimos das.

Prestar atencin particular al aumento de los slidos de baja gravedad especfica, MBT y VP.

Slidos vs. CarbonatosAnlisisDespus de la evaluacin completa de los slidos, examinar la qumica del lodo: Si el pH disminuye y la Pf aumenta o sigue igual, esto constituye la primera seal de un problema de carbonatos.

Si el pH disminuye y la Pf tambin disminuye, el problema est probablemente relacionado con los slidos.

CONTAMINACIN DE SULFURO DE HIDRGENO (H2S)

Contaminacin de H2SFuentesFormacin

Bacterias Anaerobias (generalmente insignificantes)

Agua de preparacin (generalmente insignificante)

Contaminacin de H2SIndicadoresAumento de la viscosidad, punto cedente y esfuerzos de gel en la lnea de flujoDisminucin del pH y de las alcalinidadesOlor sulfuroso ftido en la lnea de flujoOscurecimiento del lodoLa columna de perforacin se vuelve negra

Sulfuro de HidrgenoPropiedades Fsicas del LodoPeso del Lodo (MW)Sin cambioViscosidad Embudo (FV)AumentoVPSin cambio PCAumento Gel InicialAumento ligeroGel a 10 min.AumentoPrdida de FiltradoAumento ligeroSlidosSin cambio

Sulfuro de HidrgenoPropiedades Qumicas del LodopHDisminucinPmDisminucinPfDisminucinMfDisminucinCa2+Disminucin LigeraCl-Sin cambio

Sulfuro de HidrgenoReaccin QumicaH2S H+ + HS- 2H+ + S2-

Distribucin Aproximada de H2S, HS- y S2- Segn el pHpHPorcentaje de Sulfuro Total369120,010,1110100HS-H2SS2-

Sulfuro de HidrgenoTratamientoAumentar el pH a > 9,0

Amortiguar el pH > 9,0

Separar los Sulfuros mediante precipitacin

S2- + ZnO ZnS + O2-

Sulfuro de HidrgenoTratamientoSULF-X (ZnO)

1 lb/bbl elimina aproximadamente 1100 mg/l S2-

SULFATREAT1 lb/bbl elimina aproximadamente 2000 mg/l S2-

CONTAMINACIN DE SLIDOS

Contaminacin de SlidosExceso de slidos de baja gravedad especfica

Exceso de slidos finos

Contaminacin de SlidosEl efecto de los slidos sobre un lodo depende de:

ConcentracinReactividadTamao y formaCuando la temperatura de fondo aumenta, el efecto de los slidos tambin aumenta

Exceso de Slidos de Baja Gravedad EspecficaPropiedades Fsicas del LodoPeso del Lodo (MW)Aumento ligero probableViscosidad Embudo (FV)AumentoVPAumentoPCAumentoGel InicialAumentoGel a 10 min.AumentoPrdida de FiltradoDisminucin ligeraSlidosAumentoMBTAumento

Exceso de Slidos de Baja Gravedad Especfica Propiedades Qumicas del LodopHDisminucin ligeraPmDisminucin ligeraPfDisminucin ligeraMfDisminucin ligeraRazn Pf/MfSin cambioCa2+Sin cambio a aumento ligeroCl-Sin cambio a aumento ligero

Exceso de Slidos FinosPropiedades Fsicas del LodoPeso del Lodo (MW) Sin cambioViscosidad Embudo (FV)Aumento ligeroVPAumento PCAumento ligeroGel InicialAumento ligeroGel a 10 min.AumentoPrdida de FiltradoSin cambioSlidosSin cambioMBTAumento ligero si los slidos son reactivos, sin cambio si se trata de barita

Exceso de Slidos FinosPropiedades Qumicas del LodopHDisminucin ligeraPmDisminucin ligeraPfDisminucin ligeraMfDisminucin ligeraRazn Pf/MfSin cambioCa2+Sin cambio Cl-Sin cambio

Exceso de Slidos de Baja Gravedad EspecficaTratamientoRealizar un anlisis de costos para determinar si se debe aadir una centrfuga para mejorar la eficiencia del control de slidos

Aadir una centrfuga en base al anlisis de costos y operarla como unidad de recuperacin de barita

Exceso de Slidos de Baja Gravedad EspecficaTratamientoRealizar un anlisis de costos para determinar si es necesario diluir o desplazar

Desplazar con lodo nuevo o diluir en base a los resultados del anlisis de costos

Contaminacin de SlidosEfectoEl exceso de slidos aumenta la severidad de TODOS los contaminantes

Drilling cement has very little effect on a lime mud but is very detrimental to a polymer system.Carbonate/bicarbonate contamination has little affect on polymer systems, but is detrimental to systems which have a higher clay content, particularly at high temperatures.A high concentration of deflocculants minimizes the effect of contaminants.The degree to which any contaminant effects the mud is a directly related to the concentration of reactive solids

The solubility of Ca(OH)2 is inversely proportional to the pH

At a pH of 11.5 , the solubility of calcium (lime) is very low

The maximum pH of lime dissolved in water is 12.4.

Lime added after the pH reaches 12.4 will not dissolve

Un-dissolved lime is considered excess lime

% soluble calcium versus pHContamination from cement contaminated barite will occur when adding barite

The mud will be thick at the hopper discharge

This can be quickly identified by detecting an increase in pH

If a lime mud is in use, it can be detected by an increase in excess lime The physical properties help determine whether the increase in viscosity is due to solids, or chemical contamination

The increase in YP and Gel strengths indicates flocculation, which is the result of chemical contamination

This is verified by little or no increase in mud weight, PV or solids content

Changes in chemical properties are used to identify the chemical contaminant

Since cement is the only chemical contaminant that has a high pH, the pH, Pm, Pf, Mf & excess lime should all increase

Increases in the pH, Pm and excess lime are the key indicators

How much the pH increases, determines whether the soluble calcium should increase or decreaseBack-up for the last slideThe purpose of treating a contaminated mud is to restore the properties to their original values

The pH and alkalinity's must be reduced so the cement (calcium) will become soluble

Then the calcium can be precipitated as insoluble calcium carbonate by adding a carbonate

Sodium bicarbonate is preferred over sodium carbonate because the reaction results in a lower pH The best way to reduce the pH of a lignosulfonate/lignite mud is to add lignite and/or lignosulfonate.

Both these materials are organic acids which have a low pH

Therefore, these materials accomplish two objectives in restoring the original properties. They reduce the pH and deflocculate the mud.

Once the pH is reduced, the addition of sodium bicarbonate will precipitate the calcium as insoluble calcium carbonateSAPP (sodium acid piro-phosphate) has a low pH (4.8) and is an excellent deflocculant < 1400F

This limits the application of SAPP Cement attacks a PHPA polymer in two ways:

First, the O ion replaces the NH2 ions and forms ammonia (NH3)Then the calcium (Ca2+) affixes between the oxygen (O-) ion to precipitate the polymer outCement is so detrimental to a polymer system that it should be pretreated for cement contamination

The hydrogen (H-) ions from the citric acid react with the hydroxyl (OH-) ions from the cement, forming water (H2O) and reducing the pH, allowing the calcium (Ca2+) to solubilize

The sodium bicarbonate precipitates the calcium out as calcium carbonateWhen cement contamination is tolerated, the calcium is not precipitated out

Instead, the other properties are restored to their original valuesDisassociation of Anhydrite and Gyp in waterThe physical properties help determine whether the increase in viscosity is due to solids, or chemical contamination




Since the pH of Anhydrite/Gyp is 6+, the pH, Pm, Pf & Mf will all decrease

Since Anhydrite/Gyp is a source of calcium, and since the pH is reduced, the soluble calcium (Ca2+) increases

Treating the calcium out with Soda Ash accomplishes two objectives:

It precipitates the calcium out

Since Soda Ash has a pH of 11+, it also assists in increasing the pHIncreasing the pH decreases the solubility of the calcium

See next slideCalcium cannot be precipitated fast enough while drilling massive anhydrite sections

The best choice is to convert to a Gyp Mud SystemA viscosity hump will occur while breaking the mud over to a Gyp System

The viscosity hump can be minimized by dilution and adding lignosulfonate

Which is best?

Next slideMgCO3 is soluble, but this reaction is not reversibleThis reaction is reversible, depending on the pH

For magnesium to remain as magnesium hydroxide, the pH must be controlled at 10.5 or above It should be obvious that lime Ca2+(OH-) cannot sequester more calciumIn hard water, clays do not hydrate as much. Therefore, the filter cake is not as compressible. This makes fluid loss more difficult to control.

Chemicals are not as soluble in hard water. Therefore, they are not as cost effective.

Rock salt is the formation

Make-up water is seawater or brine

Formation water is a salt water flow or produced waterDisassociation of salt in waterThe physical properties help determine whether the increase in viscosity is due to solids, or chemical contamination




Since the pH of salt is 7.0, the pH, Pm, Pf & Mf will all decrease

Since salt is a form of chloride (Cl-), there will be a substantial increase in chlorides

If the salt is Na+Cl-, there will be a slight in hardness (Ca2+) due to the reduction in pH

If the salt is carnalite (mg2+) or calcium chloride (Ca2+Cl2-), there will be a large increase in hardness

Salt cannot be economically treated out. Therefore, the above options exist

Dilute with water

Add Caustic Soda to control pH

Lignosulfonate is the most effective deflocculant. The solubility of lignite decreases as the chlorides increase - not very effective at > 20, 000 mg/l ClTo prevent wellbore enlargement due to the salt formation dissolving into the water phase of the mud if a large salt section is to be drilled

This is a very difficult break-over.

Adding the salt results in severe flocculation

Therefore, it is best to mix a salt-saturated mud from scratch and displace the salt-contaminated mud

If the a break-over is required, as much as 30-40 % dilution may be required

It is best to saturate the water before dilution rather than adding the salt and water to the mud separately

Try to control the low gravity solids content less than 5% if salt is expected

Over-treatment is usually the result of pre-treatment for cement contamination

Degradation of lignosulfonate is the most common

Barite has varying concentrations of carbonates

The above is true when there is a gradual increase in carbonate/bicarbonate contamination

Flowline viscosity will also increase gradually

If a CO2 kick occurs, the increase in viscosity and gel strengths will be dramatic

When the pH is increased above 10, bicarbonates are converted to carbonates

In small concentrations, carbonates reduce the YP while bicarbonates increase the YP

See the next two slides for a graphic illustration of this

When the pH is increased above 10, bicarbonates are converted to carbonates

In small concentrations, carbonates reduce the YP while bicarbonates increase the YP

Substantial increases in the YP will occur if carbonates are converted to bicarbonates

Substantial decreases in the YP will occur if bicarbonates are converted to bicarbonates

This conversion of bicarbonates to carbonates or vice versa is a function of the pH

If the concentration of carbonate/bicarbonate contamination is high enough, the mud will solidify (see chart above)

Therefore, it is important to precipitate the carbonates out as calcium carbonate

The carbonates will deplete the calcium and form calcium carbonate

Since CO2 is an acid gas, the pH should decrease

Why does the Pm, Pf, & Mf increase when the pH did decreased?

The following slides show why

In the Pm & Pf titration, the sulfuric acid (H2SO4-), converts the OH- ion to water (HOH). The previous slide shows that this takes very little acid, since very little caustic is present.

In the Pm & Pf titration, sulfuric acid (H2SO4-), also converts carbonates (CO32-) to bicarbonates (HCO3-)

This requires a hydrogen ion (H) for each carbonate ion (CO32-) present in the filtrate. Therefore, the more carbonates present, the higher the Pm & Pf.

In the Mf titration, sulfuric acid (H2SO4), is added until the pH is reduced to 4.3, where all carbonates (CO3) and bicarbonates (HCO3) are converted to carbonic acid (H2CO3).

This requires two hydrogen ions (H2) for each carbonate ion (CO3) present in the filtrate. Therefore, the more carbonates present, the higher the Mf.

The Pf / Mf method and the pH / Pf method relate to the last three slides

The Garrett Gas Train is used to measure carbonates through a Dragger tube and is converted to mg / l total carbonates

High concentrations of lignite in muds will show an elevated Mf.

Lignite contains strong organic acids that buffer the pH between 4.3 - 8.3.

The concentration of hydroxyl, carbonate, and bicarbonate ions can be calculated if the pH, Pf and water fraction are known Adjust the pH to where majority of carbonates exist and calcium is soluble (pH 10-11)

Add a source of calcium

Calcium solubility as a function of pH

Calcium solubility is very low above 11 pH

At a pH less than 10.0 lime, will raise the pH and provide a source of calcium to precipitate out the carbonates

At a pH greater than 11.0, gyp will decrease the pH and provide a source of calcium to precipitate out the carbonates

The right concentration of high pH lime and low pH gyp will maintain a constant pH between 10.0 & 11.0 and provide a source of calcium to precipitate out the carbonates

Hydrogen sulfide from Anaerobic bacteria and make-up water is usually insignificant

If the pH is decreased to less than 9.0, the solubility of lignosulfonate and lignite is also decreasedUnless a H2S kick is encountered, the first indication of H2S contamination is an increase in flowline viscosity and 10 minute gel strength

Hydrogen sulfide is an acid gas which reduces pH, Pm, Pf, & Mf

When a hydroxyl ion (OH) is added, it reacts with one of the hydrogen ions (H+) in the hydrogen sulfide (H2S) to form a water molecule (HOH), leaving an alkaline sulfide (HS-) which is not harmful to humans or drill pipe.

Another hydroxyl ion reacts with the remaining hydrogen ion (H+) to form another water molecule (HOH), a bi-sulfide ion (S2-)

As you can see in the equation, these reactions are reversible, depending on the pH

Therefore, the bi-sulfide should be treated out with zinc oxide (ZnO)

100% H2S < 5.0 pH

1% H2S @ 9.0 pH

0.1% H2S @ 10 pHAdd caustic to increase the pHAdd lime to buffer the pHAdd SULF-X to precipitate out the S= S2- + ZnO ZnS + O2-The greater the concentration, the greater the contamination

Reactive solids increase the YP as well as the PV

Angular shaped solids create more frictional forces than rounded solids

When solids are ground into smaller size, the surface area increasesThe increase in YP and gel strengths depends on how reactive the solids areHydroxyl ions (OH-) attach to reactive solids and are removed as the solids are removed. Therefore, the pH and alkalinities are reduced If there are no reactive sites on the solids, there are no sites for methylene blue to attachIf there are no reactive sites on the solids, the hydroxyl ions (OH-) cannot attach to the solidsThis analysis should compare the cost of dilution vs displacement vs renting and operating a centrifugeThis analysis should compare the cost of dilution vs displacement vs renting and operating a centrifuge

Chemical contaminants flocculate reactive solids

The greater the concentration of reactive solids, the greater the flocculation and increase in YP and gel strengths

The greater the concentration of inert solids, the more the reactive solids will be crowded closer together, resulting in more severe flocculation

12. contaminacion.ppt

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