Lect 9-PETE517_S22_212 (Clay Chemistry).pdf

Slide ⎯
Introduction to Drilling and Workover
Fluids
Lecture [9]
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

Slide ⎯
Why clay?
3
The elements that constitute the clays account for more than
80% of the mass of the earth (Al 8%, Si 27.7%, O 46.6%), It can be
readily realized that every stage of drilling a hole brings contact
with clays.
Features of the clay minerals:
• Fine size (less than 2 µm)
• Large surface area
• Chemical reactivity of the surface
• Composed of the same chemical components

Slide ⎯
What is clay?
4
Clay is a finely-grained natural rock or soil material that combines one
or more clay minerals with possible traces of quartz (SiO2), metal
oxides (Al2O3 , MgO etc.) and organic matter.
Clay mineral is the major component of clay. Its crystal structure and
basic characteristics have a direct impact on the performance of
drilling fluid.

Slide ⎯
Clay Mineral
5
Clay mineral is the major component of clay. Its crystal
structure and basic characteristics have a direct impact on
the performance of drilling fluid.
Basic Structure of Clay Minerals
• Although clay minerals differ vastly in types and structures, they
all possess the same basic tectonic units.
• These basic tectonic units form basic tectonic sheets, then
basic tectonic sheets form basic structure layers.

Slide ⎯
Clay Minerals
6
Clay mineral is the major component of clay. Its crystal
structure and basic characteristics have a direct impact on
the performance of drilling fluid.
Clay minerals have two basic tectonic units:
1. Silicon-oxygen tetrahedron and
2. Alumina octahedron.
These two basic tectonic units form two basic tectonic sheets

Slide ⎯
Clay Minerals
7
Silicon-Oxygen Tetrahedron and Silicon-Oxygen Tetrahedron
Sheet
Silicon-oxygen tetrahedron is composed of a silicon atom and four
much bigger oxygen atoms located equidistantly to this silicon atom

Slide ⎯
Clay Minerals
8
Silicon-Oxygen Tetrahedron Sheet
Silicon-oxygen tetrahedron sheet is formed by multiple silicon-oxygen
tetrahedrons sharing bottom oxygen atoms
Each silicon-oxygen tetrahedron sheet has bottom oxygen atom plane and top
oxygen atom plane.
The bottom oxygen plane contains more oxygen atoms than the top oxygen
plane.

Slide ⎯
Clay Minerals
9
Silicon-oxygen tetrahedron sheet is formed by multiple silicon-oxygen
tetrahedrons sharing bottom oxygen atoms

Slide ⎯
Clay Minerals
10
Silicon-oxygen tetrahedron sheet can extend further in the plane,
forming a structure with continuous hexagonal grids
The inscribed circle diameter of this hexagonal grid is around 0.288 nm,
while the thickness of silicon-oxygen tetrahedron sheet is about 0.5 nm.
Hexagonal
Hole

Slide ⎯
Clay Minerals
11
Alumina Octahedron and Alumina Octahedron Sheet
Alumina octahedron is formed through coordination between an
aluminum atom and six oxygen atoms

Slide ⎯
Clay Minerals
12
Alumina Octahedron and Alumina Octahedron Sheet
• Alumina octahedron sheet is constructed by sharing oxygen
atoms.
• There are two parallel planes of oxygen atoms (or hydroxyl
groups) in the aluminaoctahedron sheet.
• All the oxygen atoms (or hydroxyl groups) in the alumina
octahedron sheet distribute in the two planes

Slide ⎯
Clay Minerals
13
Structure of the clay mineral
The basic structure layer (also called crystal layer) of clay mineral is
constructed by silicon-oxygen tetrahedron sheet and alumina
octahedron sheet bonding with each other at different ratios

Slide ⎯
Clay Minerals
14
Structure of the clay mineral
Unit Layers Structure

Slide ⎯
Clay Minerals
15
Types of clay minerals
• Different combination of tetrahedron and octahedron sheets forms
different clay minerals
• Clay minerals are constructed by stacking of the two kinds of basic structure
layers
1:1 → 1-tetrahedron to 1-octahedron
2:1→ 2-tetrahedron to 1-octahedron

Slide ⎯
Clay Minerals
16
• Single tetrahedron attached to the octahedron
• Balanced charges within the structure
• Crystal layers are joined tightly through hydrogen bonds and
intermolecular forces

Slide ⎯
Clay Minerals
17
Example- Kaolinite
Difficult for water layer to enter the
crystal structure
Non-expansive clay (No swelling)
Replacement of silicon or
aluminum is rare
Exchangeable cations on crystal
surfaces is rare
Si
Al
Si
Al
Strong
Hydrogen
bonds

Slide ⎯
Clay Minerals
18
• Two tetrahedron attached to the
single octahedron
• All the top oxygen atoms in
oxygen silicon tetrahedron point
toward the alumina octahedron
• Silicon-oxygen tetrahedron
sheets and alumina octahedron
sheets bond with each other by
sharing oxygen atoms.

Slide ⎯
Clay Minerals
19
• Two sides of crystal layers are
composed purely of oxygen
atoms
• No hydrogen bonds exist
• The crystal layers are loosely
bonded and water can get into
the structure easily.
• Large number of exchangeable
cations in the crystal surface
Example- Montmorillonite
Si
Si
Al
Weak
bond
Si
Si
Al

Slide ⎯
Clay Minerals
20
Common clays
Illite
• Difference between illite and
montmorillonite is that for illite the
lattice substitution mainly takes place in
the silicon-oxygen tetrahedron sheets
• Exchangeable cations for the
electrovalence compensation are mainly
potassium ions
• Difficult to release potassium ions
Type 2:1
Si
Si
Al
Joined
by K+
Si
Si
Al
K+
K+ K+ K+ K+

Slide ⎯
Clay Minerals
21
Common clays
Chlorite
• Interlayer space is filled by
brucite Mg(OH)2 sheets
• Hydrogen bonds exist between
crystal layers of chlorite
• Crystal layers of chlorite are
tightly bonded and water cannot
enter the interlayer easily
• Non-Swellable
Type 2:1
Si
Si
Al
Brucite
Mg(OH)2
Si
Si
Al

Slide ⎯
Clay Minerals
22
Common clays
Palygorskite and Sepiolite
• Palygorskite and sepiolite
are both chain-layered clay
minerals
• Structure combines the
characteristics of both
chain-like clay minerals and
layered clay minerals
Type 2:1

Slide ⎯
Clay Minerals
23
Common clays
Palygorskite and Sepiolite
Crystals are slender and
easily assembled to bundles,
with fiber-like appearance.
Good water solubility and can
entangle with each other to
generate structural viscosity
Salt-resistant clays.
Type 2:1

Slide ⎯
Clay Minerals
24

Slide ⎯
Clay Minerals Properties
25
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).

Slide ⎯
26
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.

Slide ⎯
27
Reactive Property
For acidic conditions
Hydroxyls on the surface of clay minerals can react with H+, which makes the surface
of clay minerals electropositive.

Slide ⎯
28
Reactive Property
For alkaline conditions
Hydroxyls on the surface of clay minerals can react with OH−, rendering the surface of
clay minerals electronegative..

Lect 9-PETE517_S22_212 (Clay Chemistry).pdf

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