Mud Viscosities and Other Rheological
shear stress and shear rate. Another
Properties (Viscosity, Gel Strength and
property that is crucial in a drilling mud is
Yield Point)
its yield point.
Yield point is the
characteristic for minimum stress, below
Nor Syamimi binti Mohd Asymawi Asymawi
which flow does not occur. At low shear
Sofea wahidah binti Salleh
rates
there
is
a
typical
non-linear
relationship between shear stress and shear
Muhammad Masrul bin Ismail
rate, which tends to be attenuated with the Muhammad Hafizszul bin Amirusham
increase
of
shear
rate.
Whereas
for
Newtonian fluid flow is the ratio of shear
Farah Adeeba binti Jamal
stress to shear rate or viscosity is constant. Drilling Laboratory, MARA University of Viscosity of fluid is the resistance to flow.
Technology
In drilling, it is one of the most important mud properties to be controlled to ensure smooth drilling operation. Drilling mud
ABSTRACT
must have high enough viscosity to Generally, rheology is defined as the study
transport the drill cuttings from bottom
of deformation and flow behaviour of all
hole to the surface. This is to ensure that
forms of matter. In drilling engineering,
the cuttings could be removed at the
rheology refers to the shear stress/ shear
minimum velocity of the mud pump.
rate/ time relationship of drilling fluids.
Marsh funnel are popular quality-control
The
rheological
tools used in the drilling field. They offer a
properties are to design and evaluate the
simple, practical alternative to viscosity
hydraulic and assess the functionality of
measurement.
the mud system. Mud rheology has two
measurement, a single points known as
types of fluid that are non-Newtonian fluid
drainage time is used to determine an
flow and Newtonian fluid flow.
average viscosity.
For
main
purposes
non-Newtonian
of
fluid
flow,
the
Based
on
For
this
single
the
point,
normal
little
viscosity is not influenced by temperature
information is obtained regarding the
and pressure but is also strongly related to
known-Newtonian behaviour of the fluid
the velocity at which the mud flows
or the mud. It is used to determine the
through hydraulic system. It also exhibits a
rheological properties of drilling muds and
variety of different correlations between
other non-Newtonian fluids by using the
excessive friction pressure losses and,
viscosity obtained from the Marsh Funnel .
therefore,
fluid
properties
bottom
hole
circulating mud densities, which in turn
INTRODUCTION
Drilling
excessive
can for
rock
lead
to
very
problems. There
are
costly two
drilling ways
of
formations are fairly straight forward with
measuring viscosity that are qualitative
carrying capacity and lubrication being the
(relative
most important factor. The fluid must carry
(absolute measurement). The qualitative
cuttings from the bore hole and also
measurement is conducted through the use
provide lubrication to prevent excessive
of
wear on the tooling (Tyson Smith, 2011).
measurement is conducted through the use
It is mandatory to specify not only type of drilling mud for each hole interval to be drilled but also the specific properties of the muds. These are the density, flow properties or rheology, filtration and solid content as well as chemical properties. Currently,
the
problems
in
drilling
activities may contribute to high cost, thus to avoid this costly drilling problem, these properties must be field controlled and properly maintain at their optimum values. Therefore, any changes should be monitor by conducting field tests such as mud viscosities and other rheological properties experiment (J.J Azar & G.Robello Samuel, 2007). Maintaining viscosity high enough to carry cuttings from the bore is critical in maintaining penetration rates. Too little viscosity will allow cuttings to fall out of the slurry and be deposited behind the drill head. Too high of viscosity will result in
marsh
measurement)
funnel
while
or
quantitative
the
absolute
of rotational viscometer which will then allow the calculation of yield point, plastic viscosity, gel strength, power low index (n), and consistency index (K). The purpose of using marsh funnel is to detect any variation in the viscous properties of the fluid. Generally, absolute measurement or rotating viscometer is recommended because it gives a more accurate data compared to marsh funnel. From rotating viscometer, the value of PV and YP are given and these values are more important to determine the pressure drop in the circulating system. MATERIALS AND EXPERIMENTAL METHODS
The material used in this study is water based mud. There are two ways to determine the viscosity. First by using the Fann Viscometer. Second is by using the marsh funnel viscosity. We used this type of mud to determine the viscosity, gel
strength and yield point. (George V.
The Fann Viscometer is set up. The mud is
Chillingarian, Ersen Alp, Mouhammed Al-
then poured into the cup sample of the
Salem, Saffet Uslu, Sue Gonzales &
Fann Viscometer. The cup is then placed in
Ronald J. Dorovi, 1983).
the hole so that it cannot move. The rotary
In the first experiment, we used the Fann Viscometer which is also known as the direct-indicating viscometer. (Savins & Roper, 1954). There are two speeds of rotation which are 300 and 600 rpm. We change the speed by controlling the range knob. The Fann Viscometer consists of the rotary speed setting, bob, deflection dial, a cup for the mud sample and a motor.
marsh funnel viscosity. By using the marsh we
can
only
determine
the
viscosity. Marsh funnel is used to measure the viscosity by observing the time taken for the oil-based mud to flow from a cone through a short tube. Before starting the experiments, the water-based mud is mixed by the mixer machine to ensure that the mud
is
completely
dissolved
before
conducting the experiment. The mud is poured in the container until it reaches the level
marked
at
the
container.
The
container is then placed at the machine and leave for about one to two minutes so that the mud is completely mixed. Then, the mud is set to rest for also about one to two minutes.
minute. After one minute, the reading of viscometer is observed at the deflection dial and it is recorded. The gel strength and the yield point are calculated. The oil based mud is then set to rest for one minute before proceed with the next speed which is 300 rpm. The steps are repeated. For
In the second experiment, we used the
funnel,
speed setting is then set to 600 rpm for one
the
second
experiment,
as
aforementioned, we used the marsh funnel. The marsh funnel is held vertically with the end of the tube is closed by a finger. The mud is then poured through the mesh to remove the particles which might block the tube and affect our data.
When the
mud is already stable, the finger is removed. As the finger is removed the stopwatch is also started. The mud is allowed to run into a beaker. The time in seconds is recorded as a measure of the viscosity. RESULT AND DISCUSSION: Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows
easily
because
its
molecular
makeup
results in very little friction when it is in motion.
Gases
also
have
Plastic Viscosity, = 600 rpm reading 300 rpm Reading
viscosity,
although it is a little harder to notice it in
Apparent viscosity, =
ordinary circumstances. Viscosity is one the rheological properties of drilling mud together with gel or shear-strength and yield strength that needs to be measured.
Normally Bingham Plastic Model is used to describe mud properties as Plastic Viscosity and Yield Point
Rheology is the study of the deformation and flow of matter. (in this case drilling mud). It is important to know the rheology of mud because most drilling fluids are non- Newtonian fluids (that is ratio of shear stress to shear rate is not constant). The viscosity of the mud has to be measured
because
such
rheological
parameter helps to determine how drilling fluids will flow under a variety of different conditions.
Viscosity is a general term used to define
A low plastic viscosity shows that the mud
the internal friction generated by a fluid
can drill rapidly because of the low
when a force is applied to cause it to flow.
viscosity of mud exiting at the bit. The
Viscosity maybe in the form of plastic or
reverse is the case for a low plastic
apparent
a
viscosity. High plastic viscosity is caused
measure of the internal resistance to fluid
by a viscous base fluid and by excess
flow resulting from interaction of solids in
colloidal solids. To lower plastic velocity,
a drilling mud, while the latter is the
a reduction in solids content can be
viscosity of the drilling mud measured at a
achieved by dilution .
viscosity.
The
former
is
given shear rate at a fixed temperature. They are both measured in centipoises and are calculated as follows:
Another type of viscosity is Marsh or funnel viscosity measured in seconds with a Marsh funnel. This is not a true viscosity, but it is important because it serves as a
qualitative measure of how thick the mud
strength of drilling mud should be
sample is. However this is not applicable
measured and maintained in the favourable
to quantitative analysis of flow properties
range.
(Azzar and Lummus, 1986).
(a)
pressure required to start flow may
The difference between plastic viscosity
fracture a weak formation and
and funnel viscosity is the ratio of the speed of the sample fluid as it passes through the outlet tube (the shear rate) to the amount of force (the weight of the fluid) that is causing the fluid to flow (the shear stress). On the contrary, the plastic viscosity is the resistance of fluid to flow.
If gel strength is too high, the
could lead to blowout. (b)
If gel strength is too low, settled drilling mud will not effectively suspend cuttings and other debris and may allow weighting material to settle.
Having swab and surge pressures produced
Liquid drilling fluids are commonly called
by pipe movement in drilling muds having
drilling mud. All drilling fluids, especially
excessive
drilling mud, can have a wide range of
undesirable
chemical and physical properties. These
temporary over-balance or under-balance
properties are specifically designed for
of hydrostatic pressure (Devereux, 1999).
drilling
conditions
and
the
special
problems that must be handled in drilling a well. The type of drilling fluids used in our experiments is water based mud. This fluid
gel
strength
may
cause
pressure effects resulting in
From the result, the initial 10 sec of gel strength is 22.6 lb/100ft 2 and at final 10 minutes is 32 lb/100 ft 2.
is the mud in which water is the continuous
REASONS FOR YIELD POINT (YP)
phase. This is the most common drilling
MEASUREMENT:
mud used in oil drilling,
Yield point is a measure of the internal
Gel strength is similar to the yield point in the sense that both measurements are influenced by the attractive forces in the mud. The difference between both measurements is that gel strength is time dependent. This is usually done in 10 seconds and 10 minutes range. The following are some of the reasons why gel
resistance of a fluid (in this case drilling mud) to initial flow. In other words, it is the stress required to start fluid movement. This resistance is caused by the electrochemical or attractive forces in the mud under dynamic flow conditions. It is important
to
measure
this
parameter
because it reflects the ability of the mud to carry drilled cuttings out of the annulus or
hole.
The yield point of a mud can be
Based on the result observed, types of
reduced by adding deflocculant to a clay-
drilling muds and its rheological properties
based mud and increased by adding
can be determined. From the calculation,
freshly dispersed clay or a flocculant, such
the value on n is 0.363. This indicates that
as lime.
the mud is a pseudoplastic fluid. Their viscosity cannot be described by a single
It is normally expressed as:
number. Non-Newtonian and pseudoplastic
fluids
exhibit
a
variety
of
different
correlations between shear stress and shear rate. The present study has shown that, this
Yield point is similar to mud gel strength
parameter is related to each other. Next, we
in causing a sudden pressure change at the
also can summarise that Marsh Funnel is a
start of pumping. However, the major
quick
difference between yield strength in terms
qualitative information about viscosity.
of hydraulics is that gel strength will not
However, it does not provide enough data
exist once the fluid is moving and the gel
to evaluate some parameters. Therefore,
has been broken, while the effects of yield
rotating viscometer is best recommended
point will not disappear when the fluid is
apparatus.
moving. Gel strength is a status-dependent
prevented, the data obtain slightly deviates
property of a mud. Its value depends on
from the actual data. The errors may occur
how well the gel is formed.
due to the
and
efficient
Since
way
errors
of
finding
cannot
be
some factors that affect the
yield point of water-based drilling mud such as, temperature, and contaminant.
CONCLUSION
REFERENCES
From the experiment, we can conclude that there are two ways to measure the viscosity that is relative and absolute measurement. For
absolute
measurement,
we
can
determine parameters which are plastic viscosity, gel strength, and yield point.
1. Jones P.H. (1937). Field Control of Drilling Mud 2. George V. Chillingarian, Ersen Alp, Mouhammed Al-Salem, Saffet Uslu, Sue Gonzales & Ronald J. Dorovi
(1983).
Drilling
Fluid
Evaluation
Using
Yield
Point-
Plastic Viscosity Correlation.
(2007). Drilling Fluids. In Drilling
3. Jose Carlos Vieira Machado & Atila
Fernando
Lima
Aragao
(1990). Gel Strength As Related to Carrying
Capacity
of
9. Azhar, J. J., & Samuel, G. R.
Drilling
Fluids. doi : 10.2118/21106-MS
Engineering
(p.
Oklahoma,
USA:
R.
Equipments Evaluating
Drilling Fluids
Composition
N.J.,
Gray. &
(2011).
Procedures
Drilling and
For
Fluids.
In
Properties
of
A.,
Drilling and Completion Fluids
Guillot D. & Maitland G.C. (1988).
(6th ed., pp. 95-101). United States,
The
AL: Gulf Professional Publishing.
Rheology
Gavignet
PenWell
10. Ryen Caenn., C.H.Darley H., &
A Direct-Indicating Viscometer for
5. Alderman
Tulsa,
Corporation.
George
4. Savins J.G. & Roper W.F. (1954).
49).
of
Water-Based
Muds. doi : 10.2118/18035-MS
11. Ryen Caenn., C.H.Darley H., &
6. E. Kaarstad, SPE, B.S. Aadnoy, SPE,
and
SPE,
of Drilling Fluid. In Composition
University of Stavanger: A Study
and Properties of Drilling and
of Temperature Dependent Friction
Completion Fluids (6th ed., pp. 95-
in
101). United States, AL: Gulf
Wellbore
T.
Fjelde,
George R. Gray. (2011). Rheology
Fluids,
119768-
MS, http://dx.doi.org/10.2118/1197 68-MS
Professional Publishing. 12. Balhoff, M. T., Lake, L. W.,
7. Quigley, M.C., Mobil R and D
Bommer, P. M., Lewis, R. E.,
Corp.: Advanced Technology for
Weber, M. J., & Calderin, J. M.
Laboratory
of
(2011). Rheological and yield stress
Drilling Fluid Friction Coefficient,
measurements of non-Newtonian
19537-MS,
fluids
http://dx.doi.org/10.2118/19537-
Journal of Petroleum Science and
MS
Engineering,
Measurements
8. Tyson Smith. (2011, November
using
a
Marsh
Funnel.
7(3-4).
doi:10.1016/j.petrol.2011.04.008
22). Drilling Fluids and Rock
13. Roussel, N., & Roy, R. L. (2005).
Drilling: What You Need to Know.
The Marsh cone: a test or a
http://trenchlessonline.com/index/w
rheological apparatus? Cement and
ebapp-stories-action/id.1995
Concrete
Research,
35(5).
doi:10.1016/j.cemconres.2004.08.0
14. Azzar, J. J. and Lummus, J. L. (1986)
Drilling
Fluids
Optimization: a Practical Field Approach. Oklahoma: PenwWell Corporation. 15. Devereux,
S.
Technology
(1999) in
Drilling
Nontechnical
Language. Oklahoma: PenwWell Corporation. 16. Rabia, H. (1985) Oilwell Drilling Engineering:
Principles
and
Practices. London: Graham and Trotman Ltd. 17. Shale
Shakers
Committee;
American Society of Mechanical Engineers (2005) Drilling Fluids Processing
Handbook .
Oxford:
Elservier Inc. 18. H. A. EinsteinR. B. Krone. (1962). Experiments to determine modes of cohesive sediment transport in salt water. Journal
of
Geophysical
Research, 67 (4), 1451 – 1461. 19. G. V. Chilingarian & P. Vorabutr (1983) Drilling and Drilling Fluids 20. G. R. Gray, H. C. H. Darley, & W. F. Rogers (1980) The Composition and Properties of Oil Well Drilling Fluids
