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MINISTRY OF SCIENCE AND TECHNOLOGY
DEPARTMENT OF
TECHNICAL AND VOCATIONAL EDUCATION
Sample Questions & Worked Out Examples
For
PE-01012
DRILLING FLUIDS
A.G.T.I(First Year)
Petroleum Engineering
12
Ministry of Science and Technology
Department of Technical and Vocational Education
Petroleum Engineering
Sample Questions for
PE 01012 DRILLING FLUIDS
Chapter 1 Basic Functions and Requirements of Drilling Fluids
1.*
2.**
3.***
4.*
5.**
6.***
7.*
Describe the basic functions of drilling mud. (10 marks)
Define the meanings of velocity, density, and viscosity of drilling mud. (10 marks)
Explain the transmission of hydraulic horsepower to the bit. (5 marks)
Discuss briefly on the cooling and lubricating functions of drilling fluid. (5 marks)
Explain how the drilling mud support the weight of drill pipe and casing. (10 marks)
Write an account on the thixotropy and viscosity of muds. (10 marks)
Explain briefly about plastic viscosity. (10 marks)
Chapter 2 Rheological and Wall Building Properties of Drilling Fluid
8.**
Define the terms: dilution, shaker screen, centrifuge or cyclone separator, desander.
(10 marks)
9.*** Describe the Fann V-G meter briefly. (10 marks)
10.* Write short note on the term 'Yield Point'. (10 marks)
11.** Discuss the term 'Gel Strength'. (10 marks)
12.*** Define the factors affecting filtration. (15 marks)
13.* Explain about the high-pressure/high-temperature filtration. (15 marks)
14.** Describe the effect of time and pressure on filtration. (10 marks)
15.*** Discuss the filtration and wall-building characteristics of muds. (10 marks)
Chapter 3 Materials and Chemicals for Preparation of Drilling Fluid
16.* Explain briefly the manufacture of drilling fluid materials. (10 marks)
17.** Describe barium sulfate briefly. (10 marks)
18.*** Write short note on bentonite. (10 marks)
19.* Define the term 'Calcium carbonate'. (5 marks)
20.** Write an account on the meaning of lignosulfonates. (5 marks)
21.*** What are the lignins? (10 marks)
22.* Define the phosphates. (10 marks)
23.** Explain the principles of chemical treatment on drilling mud. (10 marks)
Chapter 4 Testing of Drilling Fluids
24.*** Define the meaning of density or mud weight. (5 marks)
25.* Write short note on the Magcobar mud balance. (10 marks)
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26** Discuss the filtration of drilling fluid. (10 marks)
27.*** Explain about Marsh funnel. (5 marks)
28.* Write short note on Fann V-G meter (field model). (5 marks)
29.** Describe the meaning of the term 'sand content'. (5 marks)
30.*** Discuss the function of stirring equipment. (10 marks)
31.* Explain how to analyse the drilling fluid. (15 marks)
32.** Write short notes on the terms 'chloride' and 'hydrogen sulfide'. (10 marks)
Chapter 5 Types of Drilling Fluid
33.*** Describe the classification of drilling muds. (10 marks)
34.* Describe the two types of emulsion and explain one of them. (15 marks)
35.** What are the chemical emulsions? (15 marks)
36.*** Discuss briefly the mechanical emulsions. (15 marks)
37.* Define the meaning of protecto-mul. (15 marks)
38.** Explain the functions of oil mud. (10 marks)
39.*** Discuss about the maintenance of drilling mud briefly. (10 marks)
Chapter 6 Solid Control
40.* Define the meaning of microns. (10 marks)
41.** Discuss the method of solids separation. (10 marks)
42.*** Write about the settling pit or sand trap. (10 marks)
43.* What are the shale shakers and vibrating screens. Describe them. (10 marks)
44.** Write short note on decanting centrifuge. (10 marks)
45.* Explain about hydroclones. (10 marks)
46.** Explain wet classification on the separation of solid particles. (15 marks)
Chapter 7 Engineering Data and Calculations Used in Mud Work
47.*** Explain annular velocity. (10 marks)
48.*** Describe hydrostatic head of the mud. (10 marks)
Chapter 8 Handling and Storage of Mud Materials and Chemicals
49.* Discuss the handling of sacked and bulk mud materials. (10 marks)
50.** Explain briefly about bulk mud. (15 marks)
* = Must know, ** = Should know, *** = Could know
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Ministry of Science and Technology
Department of Technical and Vocational Education
Petroleum Engineering
Worked Out Examples for
PE 01012 DRILLING FLUIDS
1. Describe the basic functions of drilling mud?
In the early days of rotary drilling, the primary function of drilling fluids was to bring the cuttings
from the bottom of the hole to the surface. Today it is recognized the drilling fluid has at least ten
important functions:
1. To remove the cuttings from the bottom of the hole and carry them to the
surface.
2. To cool and lubricate the bit and drill string.
3. To wall the hole with an impermeable cake.
4. To control subsurface pressures.
5. To hold cuttings and weight material in suspension when circulation is interrupted.
6. To release sand and cuttings at the surface.
7. To support part of the weight of drill pipe and casing.
8. To reduce to a minimum any adverse effects upon the formation adjacent to the hole.
9. To insure maximum information about the formations penetrated.
10. Transmit hydraulic horsepower to the bit.
2. Define the meanings of velocity, density and viscosity of drilling mud.
Velocity is the rate at which mud circulates, and the annular velocity is an important factor in
transporting the cuttings to the surface. Annular velocities between 100 and 200 ft/min are frequently
used. Velocity is dependent upon pump capacity, pump speed, bore hole size, and drill pipe size.
Calculations for annular velocity are made as follows:
Pump Output (bbl/min)
Annular Velocity = ----------------------------------Annular Volume (bbl/100 ft)
Density is weight per unit volume of mud and has a buoyant effect upon the particles.
Increasing mud density increases its carrying capacity.
Viscosity is significant in affecting the lifting power of mud. Viscosity depends upon the
concentration, quality, and dispersal of the suspended solids. In the field it is measured as a timed rate
of flow using a Marsh funnel. Viscosity is also measured with the Fann or Stormer viscometer. These
instruments are valuable aids in
measuring the effectiveness of drilling mud controls, as shown by viscosity changes in pilot tests.
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3. Describe the Rheological Model’s briefly.
Rheological Model’s
The science related to the flow of fluids or drilling mud is known as rheology. The rheological
properties are important for control of the hydrodynamic properties of both drilling mud in drilling,
and for cement in cementing operations.
When fluids are run on a rotational viscometer, they are classified according to the consistency
curve developed by plotting shears stress versus shear rate. There are four types of ideal flow
patterns: (1) Newtonian, (2) pseudoplastic, (3) dilatant, and (4) Bingham plastic. The properties of a
fluid are frequently determined, not by a single ideal flow pattern, but by a complex of rheological
properties.
The consistency curve of Newtonian fluid is characterized by a straight line passing through the
origin for all values of shear rate. Shear stress is directly proportional to shear rate (Figure 2-1-A).
The viscosity of a Newtonian fluid is constant, regardless of the rate of shear (Figure 2-1-B).
Newtonian fluids-water, glycerin, etc, are simple fluids, and viscosity is a result of molecular
attraction. The two factors affecting the viscosity of Newtonian fluids are temperature and pressure.
Figure 2-1. (A) Flow Curve of Newtonian Fluid, Shear Stress Vs. Rate of Shear
( B) Viscosity of Newtonian Fluid with Varying Rate of Shear
Non-Newtonian is a term applied to a fluid whose viscous resistance is a function of the flow
conditions. A single point viscosity measurement has little significance with non-Newtonian fluids.
The single point viscosity determination does not represent the complete flow behavior, but rather a
single viscosity out of an infinite number of viscosities. In order to determine the flow behavior of
these fluids, the flow resistance must be measured at least two shear rates. Figure 2-2 shows the
consistency curve of the various non-Newtonian fluids: (1) plastic, (2) pseudoplastic, (3) dilatant.
Drilling muds may fall into any of these catagories. Figure 3 shows how the viscosity of these fluids
vary with shear rate.
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Figure 2-2. Consistency Curves for Non-Newtonian Fluids-Plastic, Pseudo-Plastic and
Dilatant
Figure 2-3. Viscosity Changes of Non-Newtonian Fluid at Variable Shear Rates
The mud engineer is concerned with the flow patterns of these non-Newtonian fluids. Referring to
Figure 2-2 , it is noted that as soon as shear begins, the fluid will begin to flow for both the
pseudoplastic and dilatant fluids. However, the pseudoplastic fluid gets thinner at increasing shear
rate whereas the dilatant fluid gets thicker or more viscous. For the plastic fluid, a definite force must
be applied before any flow or movement begins (Figure 2-2). This is demonstrated by the consistency
curve intersecting the stress line at some point other than the origin. Like the pseudoplastic fluid, the
plastic fluid experiences decreased viscosity at increased shear rate (Figure 2-3).
If a consistency curve for a drilling mud is made with a rotational viscometer, a non-linear curve
is formed that does not pass through the origin. The phenomenon causing the intercept to occur at
some point other than the origin is due to the minimum force required to start the flow because of the
gel properties of the mud. As this force is increased, flow increases and there is a transition from plug
to viscous flow, up to the Bingham yield point is exceeded, equal increments of stress will produce
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equal increments of stress will produce equal increments of shear, and the system assumes the flow
pattern of a Newtonian fluid. (Figure 2-4)
Figure 2-4 Flow Diagram for Newtonian and Plastic Fluids
Viscosities in A typical flow curve for a drilling mud taken on the Fann V-G meter is illustrated
in Figure 2-5. The slope of the straight line portion of the consistency curve is proportional to plastic
viscosity. Instrument constants have been built in so that plastic viscosity and yield point are obtained
from dial readings for two rotor speeds, 300 and 600 rpm. Plastic viscosity in centipoises is equal to
the 600 reading minus the 300 reading. The yield point, in lb/100 sq.ft. is equal to the 300 reading
minus the plastic viscosity.
Figure 2-5. Typical Flow Curve of Mud Using the Fann V-G Meter
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The components of flow, plastic viscosity and yield point, are absolute flow properties. They
reflect the colloidal and surface active behavior of solids present in drilling fluids. Both properties
affect apparent viscosity as measured by the Mash funnel and the Fann V-G meter. Measurements of
plastic viscosity and yield point are extremely useful in determining the cause of abnormal drilling
fluids.
4. Define the terms: dilution, shaker screen, centrifuge or cyclone separator, and desander.
1. Dilution – In most cases, water is added to dilute the solids concentration, which in turn
lowers the apparent viscosity and plastic viscosity by decreasing friction between the
particles.
2. Shaker Screen – Running the mud over the shaker screen removes the larger particle size
solids, reducing solids concentration. Running water on the shaker screen washes fine cuttings
into the mud and should be avoided.
3. Centrifuge or Cyclone Separator – These machines mechanically separates solids by their size
and mass. This in turn reduces the total solids concentration.
4. De-sander – This machine mechanically removes the sand from the mud, which reduces the
solids concentration.
5. Write short note the term of yield point.
Yield Point (lb/100 sq.ft)
Yield point, the second component of resistance to flow in a drilling fluid, is a measurement
of the electro-chemical or attractive forces in a mud. These forces are a result of negative and positive
charges located on or near the particle surfaces. Yield point is a measure of these forces under flow
conditions and is dependent upon: (1) the surface properties of the mud solids, (2) volume
concentration of the solids, and (3) the electrical environment of these solids (concentration and types
of ions in the fluid phase of the mud). High viscosity, resulting from high yield point or attractive
forces is caused by:
1.
Introduction of soluble contaminants such as salt, cement, anhydrite, or gyp, which
neutralize the negative charges of the clay particles. Flocculation and increased yield point
result.
2.
Breaking of the clay particles by the grinding action of bit and drill pipe, creates new
residual forces (broken bond valances) on the broken edges of the particle. These forces tend
to pull the particles together in disorganize form or flocs.
3.
Introduction of inert solids into the system increases the yield point. this results in the
particles being moved closer together. Because the distance between each particle is now
decreased, the attraction between particles is increased.
4.
Drilled Hydratable shales or clay introduce new active solids into the system increasing
attractive forces by bringing the particles closer together, and by increasing the total number
of charges.
5.
Insufficient or over treatment with chemicals increases the attractive forces.
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Yield point is that part of resistance to flow which may be controlled by proper chemical
treatment. As the attractive forces are reduced by chemical treatment, the yield point will decrease.
Reduction of yield point will also decrease the apparent viscosity. Yield point may be lowered by the
following methods:
1. Broken bond valences, caused by grinding the clay particles, may be neutralized by
adsorption of certain negative ions at the edge of the clay particles. These residual valences
are almost satisfied completely by such chemicals as tannins, lignins, complex phosphates,
lignosulfonates, etc. The attractive forces that previously existed are satisfied by the
chemicals and the basic negative charge of the clay particle predominates so that the solids
now repel each other.
2. In the case of contamination from calcium or magnesium, the ion causing the attractive
force is removed as an insoluble precipitate thus decreasing the attractive force and yield
point.
3. Water can be used to lower the yield point but unless the concentration of solids is very
high, it is relatively ineffective and can be expensive. Water generally upsets all properties of
the mud. This is particularly true of weighted muds by increasing fluid loss, lowering mud
weight (necessitating weighting up again) lowering plastic viscosity, etc.
Yield point is a measurement of the attractive forces in a mud system or it might be said to be
a measure of effectiveness of chemical treatment under flow conditions. Equally important are the
attractive forces causing gel strength.
6. What are the lignins?
Lignins
The basic lignin used for viscosity control is TannAthin (pH-3.2). To be effective, caustic soda
must be added with the material. In field use, the ratio of caustic soda to TannAthin will range from
1:6 to 1:1. The lignins are best added through the mud hopper. TannAthin performs best at low pH,
but works well at any pH. In addition to being an effective dispersant, TannAthin also improves
mechanical emulsions.
Emulsite is a pre-reacted caustized lignite used primarily for low pH muds. It is alkaline because
it has been reacted with caustic soda. Being a pre-reacted compound it is much more soluble than
lignin, Thus more effective. Emulsite is used primarily in low pH muds and additions can made either
through the chemical barrel or mud hopper. Like TannAthin, Emulsite is also a good mechanical
emulsifier.
XP-20 (pH – 10) is a pre-reacted chrome lignite used primarily in conjunction with Spersene
(Magcobar’s chrome lignosulfonate compound). It complements the performance of Spersene in
Magcobar’s lignosulfonate mud system
( XP – 20 / Sperence). As an integral part of the XP20/Sperence mud system, XP-20 is a drilling fluid stabilizer and emulsifier; it decreases fluid loss and
contributes to the inhibitive properties of the mud. The application of XP-20 is not limited only to
XP-20/Spersene mud, but can also be used in a regular low pH fresh water mud.
The lignite materials are not effective at high calcium concentration and only moderately
effective at high salt concentration.
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7. Write short note on the Magcobar mud balance.
Magcobar Mud Balance
The Magcobar mud balance (Figure 4.1) consists principally of a base on which rests a
graduated arm with cup, lid, knife edge, level vial, rider and counterweight. The constant volume cup
is affixed to one end of the graduated arm, which has a counterweight at the other end. The cup and
arm oscillate in a plane perpendicular to the horizontal knife edge, which rests on the support, and are
balanced by moving the rider along the arm.
Figure 4.1. Magcobar Mud Balance
8. Define the classification of drilling muds.
Additional methods of classification are used to further differentiate mud systems such as
lime-starch, lime-starch-emulsions, salt water-starch, Gyp-Q-Broxin, stabilized, low surface tension,
calcium-surfactant, petronate, E.P. etc. These are attempts to more closely restrict the mud
composition or properties to local terminology or for greater exactness.
1. Natural Muds – No Treatment
2. Fresh Water Muds (sodium chloride less than 1%; calcium ions less than 120 ppm)
a.
Low pH- Phosphate (pH to 8.5)
b.
Caustic- Quebracho (pH 8.6 to 10.5)
c.
High pH (pH 12.0 to 13.0)
d.
Chrome Lignosulfonate (pH 8.5-10.0)
3. Saline (monovalent) Muds (sodium chloride 1.0% or greater)
a.
Brackish Water
b.
Sea water (approximately 3.5% NaCL)
c.
Saturated Salt Water
4. Calcium (Polyvalent)Muds
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5.
6.
7.
8.
9.
a.
Low Lime
b.
High Lime
c.
Gypsum
d.
Calcium chloride, acetate, or other polyvalent cations.
Low Solids Muds (solids less than 7% by volume)
Oil Emulsions, Oil to 15% in Water
Invert Emulsions, Water (20 to 70 %) in Oil
Oil Base
Sodium Silicate (Obsolete)
9. Define the meaning of microns.
Microns
Figure 6.1 is a magnified scale drawing (1 to 68) of screen sizes increasing from 12 mesh to
325 mesh. A 200 mesh screen is used for the API Sand Test and all particles which do not pass
through the screen are classified as sand. Ninety seven percent of good quality barite will pass
through 200 mesh and 95% will pass through 325 mesh (44 micron). Thus, barite will be classified in
the same category as silt. Premium clays, such as Magcogel, will fall in the colloidal range, i.e, 2
microns or less.
Figure 6.1. Magnified Scale Drawing (1 to 68) of Screen Sizes vs. Micron size
There is no mention of the type of material in the API definition of “Silt” or “Sand”. Silt may
include slimes, shales, fine quartz sand, and commercial barite. Sand may include quartz sand, shale,
bits of lost circulation material, and coarse barite. The extended use of diamond bits will contribute a
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very large fraction of drilled solids to both of these categories because its cutting action is one of
grinding and scratching rather than goughing and crushing as is effected by a tooth type rock bit.
The term “Clay”, as applied to drilled mud, is usually defined as any material that gives
plasticity when water is added. Normally, these are through of as being only the commercial
materials that are added to muds; premium clay and bentonite, but drilled cuttings and barite can act
as clay if they are ground down to colloidal size. Figure 6.2 illustrates how such could happen. It is
then, this “Clay” fraction which produces most of the viscosity in drilling muds and it is these which
must be controlled for economy and efficiency of operation.
10. Define the methods of freeing fish.
Methods of Freeing Fish
In spite of all precautions, stuck pipe still occurs. The problem then is to recover the fish by
any one of several methods:
1. Working it loose, washing over, taper tap, overshot, etc.
2. Reduction of hydrostatic pressure by water or oil.
3. Application of a Drill Stem Test tool. (Pipe is backed off and a Drill Stem Test tool with
open-ended drill pipe below is screwed into the fish. When the D.S.T. tool is opened,
differential pressure is relieve, freeing the pipe.
4. Spotting of various fluids around the fish, such as oil-base mud, invert oil mud, saturated
salt water, acid, and a special surfactant material (Pipe Lax) that is added to crude oil,
kerosene, or diesel oil.
All of the foregoing have tried with varying degrees of success. The spotting method involves
placing solutions of the varies types around the fish. The most successful method to date has been
with a soak solution of Pipe Lax and oil. Oil, alone, has been used for years with some success; but
Pipe Lax and oil mixed together has had much greater success. Pipe Lax is an additive specifically
designed to free wall stuck pipe. One gallon of the material is added to each barrel of oil to be
spotted.
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