The fifth presentation of a series of presentations on Operations Geology. Very basic, just to introduce beginners to operations geology. I hope the end users will find this and the following presentations very helpful.

1. OPERATIONS GEOLOGY
PRESENTATIONS
Presentation 5:
Drilling Mud
4 November 2016Ali Trichelli

2. Introduction
 Drilling fluid or drilling mud as many people call it, is a vital element of the drilling process. In this presentation the
following topics will be covered:
 Drilling Mud Circulating System
 Drilling Mud Types
 Drilling Mud Functions
 Drilling Mud Properties & Additives
 Drilling Mud Tests

3. Drilling Mud Circulating System
As seen in an earlier presentation, The major
components of the circulating system are:
 Mixing equipment: a hopper, a mud gun and
agitators to mix chemicals, fluids and solids to
prepare the drilling mud
 Mud pits: a series of interconnected steel tanks to
store mud & equipped with agitators to maintain
the density of the drilling mud
 Mud pumps: designed to circulate drilling fluid
down the drill string and back up the annulus
 Mud cleaners: Shale shakers, sand traps, degasser,
desander, desilter, mud cleaner centrifuge and
cutting dryer used to separate drilling mud from
rock cuttings, solids & fluids

4. Drilling Mud Types
 Water Based Mud: is the most common drilling fluid; water is the liquid phase of a water based mud. Clays and other special
additives are added to the water to make a mud with properties needed to perform the drilling operation properly. The water may
be fresh water, sea water or salt water (concentrated brine).
 Oil Based Mud: oil is the liquid phase of an oil based mud. This mud has many advantages: it stabilises the formation, reduces the
downhole drilling problems. However, it might be a problem for the drilling crew to work with as it creates slippery conditions and
environmental precautions must be used. Oil spills are to be avoided and oil must be cleaned off the cuttings before they are
disposed of.
 Drilling with Air (or natural gas): Air compressors are used instead of mud pumps; advantages: prevents formation damage,
overcomes severe lost circulation problems and allows the bit to drill fast; limitations: can not drill formations containing large
amounts of water as wet cuttings mixes up with air or gas and plugs the hole.
 Foam Drilling: If some water is present in the formation being drilled, a foaming agent can be injected into the air stream. The foam
helps separate the cuttings and remove water from the hole.
 Aerated Drilling: used in some cases; helps prevent clogging of the wellbore. With aerated drilling, both mud and air are pumped
into the drill string at the same time.

5. Drilling Mud Functions
 Clean the hole & Lift cuttings to the Surface: Mud jets out of the bit and moves cuttings away from the bottom of the hole. Then the
mud carries the cuttings up the annulus and to the surface for disposal.
 Cool & Lubricate the Drill String: Deep formations are very hot and friction from the rotating drilling string creates heat downhole. High
temperatures increase drill string and bit wear. Drilling fluid help reduce the temperature and lubricate the drill string and also helps
prevent wear.
 Protect the Wellbore Walls: The drilling fluid stabilizes the hole and keeps it from caving in by creating what is known as mud cake (the
liquid part of the mud penetrates the permeable formations and the solid particles which will be left behind, hence creating this mud
cake).
 Control the Formation Pressure: The column of mud in the well creates pressure downhole called hydrostatic pressure to
counterbalance the formation pressure. As long as the well is full of mud with the right mud weight, the well will not kick or blow out. A
kick is the entry of formation fluid into the well bore which forces the drilling mud out of the hole. This kick occurs when the formation
pressure becomes greater than the hydrostatic pressure. If the kick is not controlled then it can cause a blow out, which is an
uncontrolled flow of drilling mud and formation fluids out of the hole.
 Obtain Downhole Information: by examining cuttings at surface and evaluation of hydrocarbon shows, important information on the
formations being drilled and the downhole conditions can be gathered.

6. Drilling Mud Properties & Additives
 Bentonite: is a clay added to the water or oil based mud in order to thicken the mud, give it viscosity to help clean the cuttings from the
hole and provide other desirable properties.
 Barite: is a heavy mineral; it is added to the mud to make it heavy or dense. Weighted mud controls formation pressure; this is called
primary well control.
 pH: the control of manymud properties depends on its pH, which is the measure of the mud acidity or alkalinity. The ph scale runs from
zero to 14. Most drilling muds require a higher ph ( 9 or above).
 Caustic Soda: This additive is used to increase the ph of the mud and makes it alkaline. Caustics are the most dangerous chemicals to
handle on the rig. A proper personal protective equipment is to be worn when handling this chemical.
 Gelled Mud: When drilling stops (to make a connection for example), the driller normally stops pumping mud. When pumping stops,
the mud stops moving and becomes a gel (a semi-solid). Gelled mud suspends the cuttings and prevents them from falling downhole
and piling up around the bit. The ability of a mud to keep the cuttings suspended is measured by its gel strength. When the mud
circulation resumes, the gel strength reduces and the drilling mud can flow easily.

7. Drilling Mud Tests
On the rig, it is very important that the drilling mud properties covered on the previous section are constantly
monitored and maintained. An important member of the drilling team at the wellsite is the mud engineer.
The mud engineer runs tests on the drilling fluid, monitors and maintains the mud properties and recommends
changes to improve drilling if needed.
The following are tools used to monitor mud properties:
 Mud Balance: Measures the density, or the weight per unit volume, of the mud. Density of the drilling mud
determines the hydrostatic pressure of the mud column; hence it is very important to know the mud density at all
times. Mud density, also called mud weight, is measured in pounds per gallon ppg or specific gravity sg or kg per
liter.

8. Drilling Mud Tests (Continued)
 Marsh Funnel: measures the viscosity of the mud (or its
resistance to flow). The mud’s viscosity is an important
parameter to know as it determines how well it can
carry cuttings up to surface and out of the hole.
Viscosity is the time in seconds of one quart (956 cc) of
drilling mud flowing through a special funnel called
Marsh Funnel.
 Rotational Viscometer (or Fann V-G meter): This is an
other device that measures mud viscosity. It is made of a
rotational cylinder and bob (rotor) instrument; Two
speeds of rotation, 300 and 600 rpm, are available in all
instruments. The unit of measurement is centipoises. In
addition to viscosity, this viscometer measures the yield
point or the mud resistance to flow. Combined with a
timer, it measures the gel strength ( the mud’s ability to
temporarily solidify or gel when it is not flowing).
Marsh Funnel
Rotational Viscometer

9. Drilling Mud Tests (Continued)
 Filter Press: is a pressurized cell, fitted with a filter medium,
to determine the filtration characteristics of a drilling fluid
while it is either static or stirred (to simulate circulation). By
measuring the amount of filtrate, the mud engineer can get
an indication of the amount of filtrate that will be lost to
downhole formations and the amount of solids or wall cake
buildup on the wall of the hole.
 Chloride Test: The mud engineer can run other drilling mud
tests on the mud; one common test is the chloride test,
which is testing for salt or chlorides in the mud filtrate. By
adding potassium chromate and other chemicals, the mud
engineer can determine if the well has penetrated a salt
dome/ formation or whether a salt water has penetrated the
well bore, which may be a sign of a kick.
Filter Press
Chloride Test

10. Next Presentation
 Casing Design
 Why Run Casing?
 Casing Classification
 Mechanical Properties of Casing
• Tension
• Burst Pressure
• Collapse Pressure
 Casing Design Criteria
 Casing Points Selection
 Other Factors Affecting Casing Points
 Design Factors
 API Design Factors