DRILLING FLUID SYSTEMS AND
ENGINEERING
(PEE355)
BY
DR. K.O. BELLO AND ENGR. B. OTAMERE
COURSE CONTENT
Introduction to drilling fluidsa. Types of drilling fluid
b. Functions of drilling fluid
Circulatory system
Geological and Environmental consideration
Selection design and Engineering of drilling fluids
Rheological properties and Laws.
The drilling fluids personnela. Duties,
b. responsibilities,
Mud pits- activities
DRILLING FLUID SYSTEMS AND ENGINEERING
Definition of drilling fluids
Drilling fluids are chemicals that are pumped
down hole to flush out the cuttings that the drill
bit produces as it bores into the various
sediments it encounters.
What is the difference between drilling fluid
and drilling mud?
DRILLING FLUID SYSTEMS AND ENGINEERING
DRILLING FLUIDS CLASSIFICATION
Drilling fluids are separated into three major
classifications:
o Pneumatic
o Oil-based or Synthetic based
o Water-based
DRILLING FLUID SYSTEMS AND ENGINEERING
o Pneumatic fluids: this type of drilling fluid system
can either be air, mist, foam or gasified mud or
aerated fluid.
 Relatively low formation pressure or depleted
zone.
 High risk of lost circulation or formation damage.
 Poor candidate for permeable zone.
 High rate of penetration in hard rock formations.
 Poor candidate for areas where large formation
fluids volumes or high-pressure hydrocarbon or
fluid-laden formation are encountered.
o Oil based fluids: it has a high percentage of oil to water
which is called oil/water ratio. The system generally
functions well with oil/water ratio from 65/35 to 95/5.
o Functions of Oil-Based Mud
 To drill troublesome shales and maintain hole stability.
 To drill highly deviated well or hole.
 To drill a formation of high temperature and high
pressure (HT/HP).
 To minimize formation damage and ensure native-state
coring
They are resistant to contaminants such salts,
and CO2 and H2S acid gases.
o Cost consideration for oil-based mud.
Cost per barrel of oil-based mud is very high
compared to a convectional water-based mud
system:
i. It can be reconditioned and reused.
 Constituents
 Base oil such as kerosene
 Brine – e.g. calcium chloride
 Emulsifier – To emulsify the water droplets, e.g. lime
Ca(OH)2 .
 Viscosifier – Amine treated bentonite.
 Fluid loss agent.
 Weighting Agents - Barite
o Environmental impact consideration for using
oil-based muds system.
The use of oil-based muds is prohibited or
severely restricted in many areas.
However, drilling with oil-based muds in some
areas, mud and cuttings require to be highly
contained and hauled to an approved disposal
site.
• The cost of containments, hauling and
disposal can increase the cost of using oilbased muds.
o Water-based muds system
Water-based muds are extensively used drilling
fluids. They are divided into three major subclassifications:
I. Non-Inhibitive
II. Inhibitive
III. polymer
Non-inhibitive fluids: they are those fluids that do
not suppress or overcome clays swelling during
drilling operations. They are generally comprised
of native clays or commercial bentonites with
some caustic soda or lime.

They contain deflocculants or dispersants such
as lignites, lignosulfonates or phosphates.

they are generally used as spud muds.
 Inhibitive fluids: they are those fluids that appreciably
retard swelling.
• Inhibitive is achieved through the presence of some
cations: typically, sodium ions (Na+), calcium ions,
(Ca++), and potassium ion, (K+) . Generally, Ca++ or K+
or a combination of both, provides the greatest
inhibition to clay dispersion. The source of the cations
is generally a salt examples are calcium chloride,
potassium chloride etc.
• These systems are generally used to drill hydratable
clays and sands containing hydratable clays.
Polymer fluids: they rely on macromolecules,
either with or without clay interactions to
provides mud properties.
• They are very diversified in their application.
These fluids can be inhibitive or non-inhibitive
depending whether an inhibitive cation is used.
• Polymers are used to viscosify fluids, control
filtration properties, deflocculate solids or
encapsulate solids.
Constituents
 Water
 Bentonite – Acts as the primary viscosifier
 Weighting Material – barite most common
weighting material
 Fluid Loss Agent – stabilised starch
 pH Control – Caustic Soda
 Dispersants – for dispersed mud Lignites
 Encapsulators – for inhibitive mud
Functions of drilling fluids