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#5 Cementing > Chapter 1 : Oil Well Cement & Cement Additives - Classification & Properties > Flashcards

Chapter 1 : Oil Well Cement & Cement Additives - Classification & Properties Flashcards

1
Q

What is the purpose of cement?

A
  1. Zonal isolation
    -effective & durable zonal isolation to prevent unwanted production
    -zonal isolation prevents fluids migration
  2. Well integrity
    -protects the surface groundwater
    -provides support to axial load of casing
    -add compressive strength to csg string while applying pressure from well activity
    -corrosion protection of csg in long term
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2
Q

What happen to casing if fail too isolate HC sources early during well construction phase or later during production has begun?

A

-Abnormally pressured casing
-Gas & produced water can contaminate subsurface freshwater zones

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3
Q

Primary cementing maintains integrity of the cement sheath and the quality of zonal isolation during the well’s productive lifetime & even after P&A phase as it relates to…

A
  1. Well safety
  2. Long term integrity
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4
Q

During the Roman times, it was discovered that by mixing ___, the brick would be much stronger.

A

-calcium oxide
-silica
-water

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5
Q

In ___ , ___ and English brick mason, filed a patent for a process to manufacture “____”

A

1824, Joseph Aspdin, Portland Cement

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6
Q

The Technical Definition of Cement

A

A powder of Alumina, Silica, Iron Oxide and Magnesia burned together in a kiln,
finely pulverized and used as an ingredient of mortar and concrete

*Si & Al is important for cement

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7
Q

How is Portland Cement is Produced?

A

Limestone + clays & iron oxide (mixed & burned in a rotary kiln @ 2600-3000degF)
The components melt, exits the kiln, cools and form clinker.
The clinker is ground together with gypsum (to control the setting) and formed Portland Cement.

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8
Q

What is the 6 characteristics of Portland Cement?

A
  • hydraulic cement
  • set & develop compressive strength as a result of hydration, involving chemical reactions between water & compounds in cement
  • setting & hardening can occur if left in air or placed underwater
  • development of strength is predictable, uniform & rapid
    -set cement has low permeability & nearly insoluble in water (essential to achieve zonal isolation)
  • 4 basic components : C3S, C2S, C3SA, C4AF
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9
Q

Differences between cement & concrete?

A

Cement = clay + water + calcium oxide
Concrete = got gravels, sand particles

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10
Q

What are the 2 types of Raw Materials required to produce cement clinker?

A
  1. Calcareous material
    -contains lime, precipitated CaCO2
  2. Argillaceous material
    -from by products - containing Alumina, Silica & Iron Oxide
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11
Q

What are the mineralogical composition of Classic Portland Cement Clinker?
Mention : cement notation, common name, relative % by weight, strength contribution

A

C3S - Alite - 55-65% - High strength
C2S - Belite - 15-25% - High Strength
C3A - Aluminate - 8-14% - Low strength
C4AF - Ferrite phase - 7% - Low strength

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12
Q

What is the standard requirement for Portland Cmt/G Cmt strength?

A

500psi

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13
Q

What is the function of ASTM & API?

A

ASTM - material standard & material selection

API - for testing procedure
- API 10BR2

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14
Q

What are the 8 classes of API-ISO Portland cements? What are they arranged according to?

A

ABCDEFGH
They are arranged according to the depth at which they are placed, and the T & P to which they are exposed

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15
Q

What are the 3 degrees of Sulfate resistance (as determined by C3A content)

A
  • ordinary (O)
  • moderate sulfate resistance (MSR)
  • high sulfate resistance (HSR)

The higher the Sulfate Resistance, the lower the content of C3A, the lower the formation of sulpho-aluminates

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16
Q

What are the classification of Class A - Class H

A

Class A:
• Intended for use when special properties are not required.
• Available in O grade

Class B :
• Intended for use when conditions require moderate or high sulfate resistance.
• Available in both MSR and HSR grades

Class C :
• Intended for use when conditions require high early strength .
• Available in O, MSR, and HSR grades

Classes D, E, and F :
• This product is intended for use under conditions of moderately high T & P.
- Available in MSR and HSR grades
- also known as “retarded cements,”
The retardation is accomplished by significantly reducing the amount of faster-hydrating phases (C3S and C3A) and increasing the particle size of the cement grains.

Classes G & H
-most commonly used
-available in MSR & HSR
-obtained by grinding the Portland cement clinker (consisting of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an interground addition)
• No additions other than calcium sulfate or water, or both, shall be interground or blended with clinker during manufacture of Class G cement.
• The cement manufacturer is prohibited from adding special chemicals, such as glycols or acetates, to the clinker. Such chemicals improve the efficiency of grinding but have been shown to interfere with various cement additives.

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17
Q

What are the 7 major categories of Cement Additives?

A

A, R, FL, D, E, WA, SA

  1. Accelerator
  2. Retarder
  3. Fluid loss
  4. Dispersants
  5. Extenders
  6. Weighting Agent
  7. Special additives
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18
Q

What is the functions of Accelerators? Uses what?

A

FUNCTIONS:
-shorten/reduce the TT or ST of a cement slurry
-can aid in early strength development by accelerating the hydration of chemical compound of cement

USES:
-inorganic salt to accelerate the set of cement
-salts act as a catalyst rather than being incorporated with chemical reactions of the cement

19
Q

Example of Accelerators? And its characteristics

A

Calcium Chloride (CaCl2)
Sodium Chloride (NaCl)
Sodium Silicate
Seawater

  1. Calcium Chloride (CaCl2)
    -common accelerator
    -used at 1-3% concentration - above 3% can caused gelation
    -Should not be use with Silicate Extenders - system will form Calcium Silicate gel structure
    -Effects of CaCl2 - heat of hydration
    - reduced Sulphate Resistance
    - increases Slurry rheology
    - contribute to cement shrinkage
    - initial reduction of permeability & increase in later stage
  2. Sodium Chloride (NaCl)
    -not as strong as CaCl
    - < 5% act as accelerator
    - 5-10% neutral to TT
    - > 10% act as retarder
    -max acceleration occurs at 3% concentration by weight of water (bwow)
  3. Sodium Silicate
    - both liq & solid act as accelerators
    - primary action: extender, secondary action: accelerator
  4. Seawater
    - reacts much like 3% NaCl solution
    - contains more salts than NaCl, hence it is useful to use in combination with CaCl for shorter TT & rapid strength development
20
Q

What is the function of Retarders? Uses what?

A

FUNCTIONS:

  • Extend or lengthen the TT of a cement slurry (therefore, these are critical for the placement of cements in most wells)

USES:

  • sugars or lignin-type materials
  • NaCl in concentrations >25%
21
Q

Examples of Retarders? And its characteristics

A

Lignosulfnates
Synthetic Retarders
Hydroxycarboxylic acids
Cellulose derivatives
Organophosphonates

  1. Lignosulfonates
    -commonly used retarders are: Sodium & Calcium Salts of lignosulfonic acids
    -Common retarders: Calcium Lignosulfonate used at lower T
    -effective with all Portland cements
    -added in concentrations of 0.1-1.5% BWOC
    -effective at 250degF(122degC) depending on its carbohydrate, chemical structure & nature of cmt
    -combination of Adsorption & Nucleation theories
  2. Synthetic Retarders
    -useful in long liners job
    -can be used in T as high as 600degF (315%)
    -have linear response to temperature giving better strength development
22
Q

What is the function of Fluid Loss Control Agents?

A

FL additives lower the rate of FL during and after the placement to prevent the dehydration of slurry

Hence, Cement FL Agents:
1. Prevents sloughing/swelling of water sensitive fms
2. Prevent bridging caused by excessive cement filter cake built up
3. Limits permeability damage/ skin damage to sensitive production zones
4. Controls the pressure decay in slurry while setting to arrest gas migration

23
Q

What is the Theory behind working of FL Agents?

A

When FL occurs across a formation, filtercake of cement solids are formed on the surface of the formation.

The FL agent will:
-decrease the filtration rate by reducing the permeability of the filtercake, increasing the viscosity of the aqueous phase, or both.

24
Q

Example of FL Agents?

A

Particulate Material
Water soluble polymers - Natural & Synthetic

  1. Particulate Material
    -carbonate powder/carbon black
  2. Water Soluble polymers
    -Water-soluble polymers can form weakly bonded colloidal aggregates in solution that are sufficiently stable to become wedged in the filter-cake constrictions.
    -They operate by simultaneously increasing the viscosity of the aqueous phase and decreasing the filter-cake permeability.
    -Cement slurries containing water-soluble polymers must be well dispersed
    -2 classes used:
    Natural - cellulose derivatives
    Synthetic - non ionic SP/ anionic cationic SP
  3. Synthetic Polymers
    -used to plug the pores of the filter cake and inhibit fluid movement.
25
Q

What are the Fluid loss Considerations?

A
  • Salt - affect most FL additives
  • When used at Low temperature - will delay the setting of cement slurry because of the retarding action of many FL additives
    -Need dispersant to be effective - help to increase effectiveness & temperature range
  • Introduce gas or foam to slurry - results in a 3 phase system that will have a lower fluid loss rate
26
Q

What is the function of Dispersants?

A

Used to modify the rheology of the cement by reducing the viscosity of a cement slurry.

Usage of dispersant:
1. reduces the pumping rate necessary to get turbulent flow for specific well condition
2. reduces the pressure exerted (ECD) on weak formations
3. reduces surface pressure & HHP requirement
4. improves ability to mix higher densities by reducing water-to-cement-ratio
5. improves ability to mix LWC slurries which has high solid contents as lightweight spheres.

27
Q

What is the primary dispersant used in cements?

A

A formaldehyde condensate of lignosulfonic acid
Example: PNS - Polynaphthalene sulfonate

28
Q

Explain Balancing Dispersant vs Slurry Stability.

A

When adding dispersant, slurry may show sedimentation and free water separation.

Stabilizers are used in Heavy Weight slurries to suspend the weighting material

We want STABLE FLOCCULATED SLURRY

29
Q

What is an Extenders?

A

Extenders are materials and systems that allow the cement slurry to be mixed at a lower density without excessive free water development.

-to reduce density
-use light weight material

30
Q

What are the 2 broad functions of Extenders?

A
  1. Reduce slurry density
    - reduces the Hydrostatic pressure during cementing, prevent loss of circulation
  2. Increase Slurry Yield
    -extenders help to reduce the amount of cement required to produce a given volume of set product. This results in a greater economy.
31
Q

What are the 3 categories of Extenders which depends on the mechanism of density reduction/yield increase?

A
  1. Water extenders
  2. Low density aggregates
  3. Gaseous extenders
32
Q

What are the examples of Extenders?

A
  1. Lightweight particles
  2. Chemical extenders
  3. Pozzola
  4. Fume silica
  5. Hollow microspheres & ceramic spheres
  6. Nitogen
33
Q

Explain Extender (a) Lightweight particles

A

-Lightweight-particle extenders reduce the slurry density because they are lighter than the cement particles.

Such extenders include expanded perlite, powdered coal, gilsonite, and either glass or ceramic microspheres.

  • Most extenders in this category are INERT with respect to the cement.

1) Attapulgite
-yield of attapulgite is independent of salinity
-highly dependent on shear
-does not impart fluid loss control to the slurry

2) Expanded perlite
-crushed volcanic glass that expands when heated to the point of incipient fusion.
-rarely used today

3) Gilsonite
-SG 1.05
-a natural asphaltite mineral
-as a black angular solid, usually supplied as a ground material
-The water requirement for gilsonite is low giving low-density cement systems with relatively high compressive strength within BHST 300°F [149°C].

4) Powdered coal
- SG 1.3
- It is coarsely ground (50% of particles between 6 and 12 mesh) and is often used to prevent lost circulation.

34
Q

Explain the Extenders - (b) Hollow Ceramic spheres (HCS) & Hollow Glass Microspheres (HGM)

A
  • densities significantly less than the density of water
  • HGM - manufactured
    HCS - obtained by separating very lightweight
    portions of fly ash through floatation
    -Both materials have a pressure limit above which the sphere will collapse.
35
Q

What is the main disadvantage of reducing water in cement to increase slurry density?

A

Difficulty of simultaneously achieve adequate:
-FL control
- acceptable slurry rheology
- no solids settling

36
Q

What is the function of Weighting agent?

A

To increase the density of the slurry not chemically

37
Q

Examples of Weighting Agent?

A

Barite
Hematite & ilmenite
Manganese tetraoxide (Micromax)

38
Q

Explain the Weighting material - (a) Barite

A
  • Barite requires large amounts of water to wet the surface, and therefore has limited use in cement slurries
  • Barite can be used in combination with other weighting agents to help limit free water development and settling
  • Slurries with densities up to 19.0 lbm/gal can be prepared with barite
39
Q

Explain the Weighting Material - (b) Hematite & Ilmenite

A
  • heavy iron ores that have large particles

Hematite:
-at high concentration, need dispersant to prevent excessive slurry viscosity

Ilmenite:
-has little effect on cement hydration

40
Q

What is the function of Loss Circulation Prevention Agents?

A

Used to combat cement lost into very permeable, cavernous or fractured formations

2 ways to prevent the loss of cement by:
- preventing fracture inducement by reducing Hydrostatic Pressure
-by forming a low permeability bridge across the permeable opening .
Common LCM can be classified as fibrous, granular and flakes.

41
Q

What are the 2 special Additives?

A

Silica
Antifoam & defomers

42
Q

Explain special additives - Silica.

A

To prevent strength retrogression.
Silica is added to cement which reacts to form stable crystalline forms at higher termperature

43
Q

What is Strength Retrogression?

A

-At temperatures exceeding 230°F (110°C), the crystalline structure of cement changes.
-The resulting structure will be higher in permeability and have lower strength.

44
Q

Explain special additives - Antifoam & Defoamers

A

-Function: to reduce the air entrainment of cement slurries

Antifoam
-works by changing the surface tension of the water and preventing foams from forming
-As such, it is added to the mix water, or dry blended into the cement prior to mixing
-2 classes of antifoam agents are commonly used: polyglycol ethers and silicones. They will prevent the formation of a foam, but once a foam is generated in a system, will do little to disperse existing foam

Defoamers
- eliminating existing foams. As noted, these are not readily available and not normally used.

#5 Cementing (4 decks)

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