Lect 10-PETE517_S22_212 (Clay Properties).pdf

Slide ⎯
Introduction to Drilling and Workover
Fluids
Lecture [10]
Rahul Gajbhiye
Department of Petroleum Engineering
College of Petroleum Engineering and Geosciences
King Fahd University of Petroleum & Minerals
Dhahran 31261, Saudi Arabia
Spring 2022
PETE-517: Fundamentals of Oilfield Chemistry
1
© KFUPM | SPRING 2022 | PETE 517: Fundamentals of Oilfield Chemistry | Chapter 03: Drilling and Workover Fluids

Slide ⎯
Objectives
2
• Introduction to Drilling Optimization
• Role of Oilfield Chemistry
• Clay chemistry
• Properties of clay minerals

Slide ⎯
Clay Minerals
3

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Clay Minerals Properties
4
Electrical Property
The electrical property of the surface of clay minerals refers to the charge symbol and
capacity when the surface of clay minerals and water contact with each other.
Certain amounts of exchangeable cations exist on the surface of clay minerals
The electrical capacity of the clay mineral surfaces can be expressed by cation
exchange capacity (CEC).
Cation: An ion that carries a positive charge
Cation exchange: A process - cations in solution exchanged with cations on
exchange sites of minerals and on mineral
Cation exchange capacity (CEC): The total amount of exchangeable cations
that a particular material can adsorb at a given pH

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5
Cation Exchange Capacity
The sum total of all exchangeable cations that a clay can adsorb
Expressed in terms of positive charge adsorbed per unit mass
cmolc = centimole of unbalanced charge
→If CEC =10 cmolc/kg
Clay can adsorbs 10 cmol of H+
Can exchange with 10 cmol K+, or 5 cmol Ca2+
Note: Number of charges, not number of ions

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6
Exchange Affinity
H+ ≥ Al3+ > Ca2+ > Mg2+ > NH4
+ > K+ > Na+
Held more strongly Held more weakly→
Ion Exchange and CEC
Sample A
- Ca2+
+ NO3-
- Mg2+
+ Cl-
- H+
+ NH4+
- K+
Sample B
- H+
+ NO3-
- HSO4-
+ NO3-
- H+
- H+
+ NO3-
Example
-
-
+
-
+
-
-
- CEC = 6 and AEC = 2

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7
Source of charge on 1:1 clays
Broken edge of a kaolinite crystal showing oxygen atoms
as the source of negative charge
All clay minerals have edge charges.

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8
Source of charge for the smectites
In the octahedral sheet means a net negative charge.
Isomorphous substitution here,
in the octahedral sheet means a
net negative charge

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9
Source of charge for the micas
1. Isomorphous substitution is in
the tetrahedral sheets
2. K+ comes into the interlayer
space to satisfy the charge and
“locks up” the structure

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10
Clay Samples

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11
CEC as a function of pH

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12
CEC of clays

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13
Reactive Property
There are two kinds of hydroxyl groups on the surfaces of clay minerals
1. Hydroxyl groups existed on the crystal layer surface of clay minerals
2. Surface hydroxyl groups generated on the edge of clay minerals during bond
breaking.

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14
Reactive Property
For acidic conditions
Hydroxyls on the surface of clay minerals can react with H+, which makes the surface
of clay minerals electropositive.

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15
Reactive Property
For alkaline conditions
Hydroxyls on the surface of clay minerals can react with OH−, rendering the surface of
clay minerals electronegative..

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16
Reactive Property
Adsorptivity
Categorized as-
1. Physical Adsorption → Through intermolecular forces
Example- The adsorptions of nonionic surfactant
2. Chemical Adsorption →Through chemical bonds
Example- Cationic surfactants
The cations can form ionic bonds with electronegative surface of clay minerals to
achieve adsorption.

Slide ⎯
17
Expansibility
Expansibility refers to the properties of volume increase of clay minerals when
contacting with water.
Expansibilities differ with different kinds of clay minerals.
According to the crystal structure, clay minerals can be divided into
expansive clay minerals and non-expansive clay minerals
1. Montmorillonite→ Expansive clay (Presence of large number of exchangeable
cation)
Mechanism –
Water will enter its crystal layer
Dissociation of exchangeable cations
Establishment of diffused double layer on crystal surface
Surface of montmorillonite is electronegative
Electrostatic repulsion among negatively charged crystal layers leads to the increase of
lattice spacing

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18
Expansibility
2. Kaolinite→ Non-expansive clay
Mechanism –
Small number of lattice substitution
Existence of hydrogen bonds between crystal layers
Establishment of diffused double layer on crystal surface
3. Illite→ Non-expansive clay
Mechanism –
Presence of K+ which will strengthen the connection

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19
Cohesion
Cohesion refers to the property of clay mineral particles (sheets) cross-linking with each
other in water under specific conditions.
Specific conditions→ Concentration of electrolytes (such as NaCl and CaCl2)
With the increased concentration of electrolytes, the diffused double layers on the
surface of clay minerals are compressed.
Resulting in reduced electricity on the edge and the surface.

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20
Cohesion
When the concentration of electrolytes surpasses certain value, it would induce cross-
linking among the clay mineral particles.
After the occurrence of cross-linking, the clay mineral cross-links can connect
with each other and spread all over water.
There are three cross-linking ways for clay mineral particles
a. edge-to-edge cross-linking
b. edge-to-surface cross-linking
c. surface-to-surface cross-linking

Slide ⎯
Drilling Fluid Properties
21
Cohesion
Drilling fluid viscosity can be increase with addition of
montmorillonite

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22
Formation Factor that can influence the viscosity of mud
Formation factors can influence the properties of drilling fluids through
cohesive characters of clay minerals
However, the treating agents can adjust the properties of drilling fluids through
cohesive characters of clay minerals
Example→ If the Ca2+ in the formation invades the drilling fluids, edge-to-
edge cross-linking and edge-to-surface cross-linking will induce increasing the
viscosity
Further Ca2+ invasion, surface-to-surface cross-linking would be induced,
causing the decrease of viscosity

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23
Mechanism of clays as a viscosifier
Prehydration Clay in dry state exist in face-to-face stacks
When the clay is exposed to water-
Negative ionic character at the mineral surface provides attractive forces for
adsorpsion of polar water molecules
Na+ at the mineral surface will associate with a charge deficient area on one
sheet and dispersion in water will create separated sheets
Ca2+ cannot effectively associate with two negative charge centres on one sheet
and must bind 2 sheets together

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24
Mechanism of clays as a viscosifier
The volume of the clay will increase, and the clay minerals will disperse into the
water phase

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25
Remedies for increase in the viscosity of mud
In fresh water clay sheets will separate and as a result the clay swells.
In sea water the hydration of the montmorillonite reduces due to the effect of
salt.
The force causing the sheets to separate are electrostatic repulsive force
between negatively charge particles.
These forces are decreased as the conductivity of the water is increased by the
addition of salts.

Lect 10-PETE517_S22_212 (Clay Properties).pdf

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