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Week 1 > Cement Chemistry > Flashcards

Cement Chemistry Flashcards

1
Q

What is Portland Cement ?

A

a hydraulic cement that reacts with water to develop compressive strength

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2
Q

Why we call it hydraulic cement ?

A

Because it requires water to set

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3
Q

How do they make cement?

A
  1. Calcareous (lime) +Argillaceous (clay)
  2. Grinding Raw material
  3. Heat it up to 1500 C in the KILN
  4. Cool it down (clinker)
  5. Grind and add gypsum
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4
Q

Why Gypsum is needed?

A

3 to 5 % Concentration Avoid Flash Set

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5
Q

Principal phases in Cement Clinker

A
  • Silicate Phases
    • C3S (55%-65%)
    • C2S (15%-25%)
  • Aluminate Phases
    • C3A (3%-8%)
    • C4AF(8%-12%)
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6
Q

C3S information

A
  • Major Component in cement
  • Contributes to all stages of strength development
  • The one that responsible for early strength development
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7
Q

C2S information

A
  • Hydrates slowly
  • Affects long term compressive strength
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8
Q

C3A information

A

Hydrates rapidly , that’s why gypsum is added

Affects :

  • Early strength development
  • Rheological behavior of slurry
  • Controlling setting and thickening time
  • Hydrated C3A is readily attacked by sulphate
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9
Q

C4AF, information

A
  • Gives color to cement
  • Little effect on set properties
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10
Q

In the hydratation what is the main binding material Produced as soon as cement in contact with water

A

CSH silicate phase

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11
Q

In the hydratation product that is Vulnerable to chemical attack Produced at the end of induction period

A
  • CH silicate phase
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12
Q

how does Ettringite form?

A

(C3A)/(C4AF) + H2O + Gypsum

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13
Q

Effect of Temperature in the cement slurry

A

High hydrations temperatures accelerates the hydration rate Higher temperature (usually) shorter thickening time

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14
Q

Effect of Mixing Energy and Shearing in the cement slurry

A

Deflocculation : Cement particle is separated from other particle Shear a stream of solid cement particles with a fast-moving liquid

The longer the mixing time or the higher the energy, the greater the amount of hydrates formed during mixing

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15
Q

Effect of Pressure in cement slurry

A
  • In general hydration rate will be increased when pressure is increased
  • Test showed that early and ultimate compressive strength increase as the curing pressure increase
  • Very important in squeeze job (WOC with OR without pressure?)
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16
Q

Uncontrolled C3A hydration (low or no gypsum)

A

Flash set

17
Q
  • Precipitation of “secondary gypsum” due to dehydration of gypsum and higher solubility of products formed Slurry gelation inevitable
  • Reversible by vigorous agitation
A

False set

18
Q

Aging Effects factors

A
  • Long Storage Periods
  • High Humidity
  • Hot Temperatures(False Set risk)
  • Carbonation
19
Q

Aguing effects on cement

A
  • Increased Thickening Time
  • Decreased Compressive Strength
  • Decreased Heat Of Hydration
  • Unpredictable Slurry Viscosity
  • Bulk Handling More Difficult
20
Q

Sulfate Resistance

A

Expansion – Loss of Compressive Strength Cracking – Damage to tubulars Low C3A content are less likely to sulfate attack HSR (High sulfate resistant C3A < 3%) MSR (Medium sulfate resitant 3% < 8%

21
Q

Strength Retrogression temperature

A

Above 230°F

22
Q

Strength Retrogression causes

A
  • Decrease in Compressive
  • Strength Increase in Permeability
23
Q

how many clasifications of cement

A

8 classifications (From A to H)

24
Q

what depends in the clasification

A
  • Sulfate Resistance
  • Surface Area
25
Q

Hydration stages of Portland Cement

A
  • Preinduction,
  • Induction,
  • Acceleration
  • deceleration,
  • diffusion
26
Q

What happend when cement is exposed to sulphates

A

Sulfates in downhole brines react with cement hydration products (Ca(OH)2) to form secondary ettringite

This causes:

  • Expansion – Loss of Compressive Strength
  • Cracking – Damage to tubulars
27
Q

The stages when mixing cement

A
  1. Physical Mixing
  2. Weting
  3. Deflocculation
  4. Stabilization/Homogenization

Week 1 (8 decks)

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