Clay chemistry understanding is important on order to understand how clay reacts with different types of fluids .

1. Basic mud school
Abdelaziz Elsayed Gabr
Drilling Rig Supervisor at Khalda Petroleum company
Previously mud engineer in EMEC in Saudi Aramco

2. Course Content
 Introduction to geology , HSE
Functions of drilling fluids
 Mud composition
Basic Calculations
 volume Calculations & material balance
Basics of chemistry
Clay chemistry
Polymer chemistry
Mud types
Rheology & mud properties
Mud tests ( WBM )
Mud Tests ( OBM)
 Mud contamination (WBM) & trouble shooting
Mud contamination (OBM) & trouble shooting
Basics of Solid control equipment
 Mud report
Mud engineering| Abdelaziz Gabr 2

3. 8. Clay chemistry

4. Agenda
• Clay definition
• Clay nature
• Basics of clay chemistry
• Types of clay
• Clay interaction
• Clay problems

5. Clay
• Determining the type of clay and its reaction will help
us to understand the way of inhibition for it.
• Clay minerals are classified as layered silicates because
the dominant structure consists of layers formed by
sheets of silica and alumina.

6. Clay nature
• Clays are usually either of the two-layer type like kaolin or
three-layer type such as montmorillonite, chlorite or illite.
• Each plate-like clay particle consists of a stack of parallel unit
layers.
• Each unit layer is a combination of tetrahedral (pyramid)
arranged silica sheets and octahedral (eight-faced) arranged
alumina sheets.

7. Clays can either be electrically neutral or negatively
charged

8. Tetrahedral sheet silica
Tetrahedral sheet silica
Octahedral sheet
aluminium
Hydroxyl
Oxygen
Magnesium or aluminum
Silicon, occasionally aluminum
Shared Oxygen Bonding

9. Clay Platelets reactions
• Charge on the edge will vary with pH
• At low pH the edges are more positive ( Active)
• At high pH the edges are more negative (Non-active)

10. Drilling Fluid Clays
• Illite
• Chlorite
• Kaolinite
• Mixed Layer
• Attapulgate
• Montmorillonite

11. • 1- Illite
• plate-like, non-swelling (or slightly swelling).
• found in formation shales
Properties
 Illite has a substitution of Al+3
for Si+4
still giving a negative
charge.
 The compensating cations are primarily the potassium ion
(K+)
 The spacing between unit layers is 2.8 Å.
 The ionic diameter of the K+ Is 2.66 Å.
 This allows the K+ to fit snugly between unit layers forming
a bond that prevents swelling in the presence of water

12. Illite with Hydrated Cations
Ca+2
Mg+2
Ca+2
Ca+2
Li+
Na+
Na+
Rb+
K+
K+
10

13. • 2- CHLORITES (THREE-LAYER CLAYS)
• In these clays, the charge-compensating cations between
unit layers are replaced by a layer of octahedral magnesium
hydroxide (Brucite).
• This layer has a net positive charge because of some
replacement of Mg +2
by Al+3
in the brucite layer .
• It does not cause significant problems unless present in
large quantities.
• Low cation exchange capacity 10-40

14. • 3- KAOLINITES (TWO-LAYER CLAYS)
• It is a non-swelling clay that has its unit layers bound
tightly together by hydrogen bonding.
• This prevents expansion of the particle because water is
unable to penetrate the layers.

15. Kaolinite
•Low cation exchange capacity
• Low viscosity slurries

16. • 4- Attapulgite (Salt Gel)
Properties
 Not found in formation shale
 it is non-swelling in Fresh water.
 Exhibit very poor filtration properties.
 Used as viscosifier in salt water mud

17. 5- Mixed Layer
• More than one clay mineral
•Examples
• montmorillonite/illite
• illite/kaolinite
• chlolrite/kaolinite

18. • 6- Montmorillonites (semectite)
• Calcium type
• plate-like (slightly swelling).
• found in formation shales ( Calcium montmorillonite
type)
• montmorillonite sodium type
Sodium montmorillonite is added to a mud to increase
viscosity and reduce fluid loss.

19. Composition
• If just one atom of Magnesium (Mg ++ ) is substituted for
one atom of Aluminum(AL+++) in the lattice structure
(arrangement of atoms), it will then possess a surplus
electron or negative charge.
• The net negative charge is compensated by the adsorption of
cations (positive ions) on the unit layer surfaces.
• This can occur by Na+ , Ca++ ,Mg++

22. Swelling mechanism
• Clays exist in nature with a stacked or layered structure, with
each unit layer roughly 10 angstroms (Å) thick.
• Each clay layer is very thin and has a huge surface area.
• In freshwater , the layers adsorb water and swell .
• This increase in number of particles with the resulting increase
in surface area, causes the suspension to thicken.

23. Relationship - Size & Surface Area
The same solid cut
in half on each face
Cut in half again
on each face
20 micron solid surface
area 2400 microns

24. Cation Effects
• Ca2+
associates with two layers
• Limited swelling and dispersion
• less surface area and associated water
Ca+2
Ca+2
Ca+2
Ca+2
12.1 A
17 A
Hydrated

25. Cation effects
• Na+
associates with one layer
• High hydration potential
• Encourages hydration and layer separation
Na+
Na+
Na
+
Na+
Na+
Na
+
Na+
9.8 A
Na+
Na+
Na+
40 A to infinite
Hydrated

27. Cation Exchange Capacity (CEC)
• The compensating cations that are adsorbed on the
unit-layer surface may be exchanged for other
cations and are called the exchangeable cations of
the clay .

28. Clay Interactions
• Aggregation: The clay in its dry state has platelets stacked in face-
to-face association, like a deck of cards.
• Dispersion: When the dry clay is placed into fresh water with no
agitation, the packets adsorb water, hydrate, and swell. Upon
agitation, the swollen packets disintegrate into individual plates or
smaller packets of plates.
• Flocculation : When agitation is stopped, clay platelets will be
mutually attracted in edge-to-edge or edge-to-face association. This
forces a structure similar to a house of cards
• Deflocculated: If an anionic chemical thinner (deflocculant) is
added, such as lignosulfonate or lignite, etc., it neutralizes the
positive edge charges on clay platelets, so they are deflocculated.

30. Aggregated State
-
-
-
-
-
+
+ +
+ Na+
Na+ Na+
Na+
Na+
-
-
-
-
-
+
+ +
+ Na+
Na+ Na+
Na+
Na+
-
-
-
-
-
+
+ +
+ Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+

31. Hydrated Clay W/Water Envelope
-
-
-
-
- + + +
+
Na
+
Na
+
Na
+
Na
+
Na
+
Na
+
Na
+
Na
+
-
-
-
-
- + + +
+
Na
+

32. Dispersed Bentonite
-
-
-
-
- + + +
+
-
-
-
-
-
+
+
+
+
-
-
-
-
- + + +
+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
-
- - -
- +
+
+
+
-
-
-
-
-
+
+
+
+
-
- - -
- +
+
+
+

33. Flocculation
-
-
-
-
-
+
+
+
+
-
- - -
- +
+
+
+
-
-
-
-
-
+
+
+
+
-
- - -
- +
+
+
+
-
- - -
- +
+
+
+
-
-
-
-
-
+
+
+
+
Na+
Na+
Na+
Na+
Na+
Na+
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-

34. Calcium Flocculation
Ca+2
Ca+2
Ca+2
+
+
-
-
+
-
+
-
-
+
-
-
+
- + +
+ - +
-
+ -
+ -
+ -
+ -
+ - + - - + -+
- - + _ +
- - + _ +
+ - +
+
+
+ +
+
+
+
-
+
+
+ -
+ - +
+ -
+
-
-
-
_
+
-
+
-
_
+
-
+
-
_
+
-
+
+
-
-
+
+
-
_
+
Ca
Ca
Ca Ca
Ca
Ca
Ca
Ca
Ca
Ca
Ca
Ca
Ca
Ca
Ca
Ca++
Ca++
Ca++
Ca++
Ca++

36. Polymeric Flocculants
- + -
+ -
+
- +
-
-
-
+ + +
- -
_
_
_
C
a
_
_ _
_

37. Deflocculation Mechanism
• Maximize electrostatic repulsion forces

38. Polymeric Deflocculants
-
Na
+ -
+ -
+
- +
_
_
-
-
+ + +
- -
_
_
_
-
-
Na
-
-
-
+
+
_
_
-
Na
+
+
-
_
_

39. -
-
-
- -
-
-
-
-
-
-
-
-
-
-
+
+
+
+
+
+
+
-
-
- -
-
-
-
-
-
-
-
-
-
- -
+
+
+
+
+
+
+
-
-
-
-
-
+
+ +
+
-
-
-
- -
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
+
+
+
+
-
- -
-
-
-
-
-
-
-
-
-
-
-
-
- -
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
+
+
+
+
+
+
+
Encapsulated Clay W/ PHPA

40. Clay Problems
• Swelling
• Dispersion

41. Clay Dispersion
• Smectite
– Swelling clay, fresh water sensitive, takes on water and
expands
• Mixed layer
– Smectite/illite layering, swells, but not same degree as
smectite, will disperse in fresh water
• Illite
– Disperses in fresh water
Kaolinite
– Subject to dispersion, not same degree as illite
• Chlorite
– Not fresh water sensitive, doesn’t swell, high iron content,
some times acid sensitive

42. End