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Lecture #4 PET ENG 313
Drilling fluids 1
Drilling fluids 1
1. The fluid circulation system
2. Types of mud
3. Functions of drilling fluids
4. Rheological properties of drilling mud
5. Weight of drilling mud
6. Drilling mud additives
7. Selection of drilling mud additives
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Covered in Lecture 4
Concepts
• Circulation system
• Functions of drilling fluid
• Rheological properties and models ofdrilling fluids
• Viscosity and Apparent Viscosity
Calculations
• Viscosity
• Apparent viscosity for differentreadings
• PV and YP for Bingham Plastic model
• n ,K for Power law
The fluid circulation system
CuttingsShale shaker
Stand
pipe
Reserve pit
Mud in annulus
Mud
pump
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Mud system
Mud tanks Mud tanks or pits is us ed by the crew to prepare the mud for circulation
Mud pumps One or more pumps t hat circulate the mud up t he standpipe and down the
drill stri ng. Duplex pumps are most common. Triplex pumps is in use but less
common.
Standpipe &
Rotary hose
The standpipe takes the mud halfway up the Derrick. The rotary hose is a
flexible hose that moves with t he swivel as it goes up and dow n in the mast.The rotary hose is connected to t he standpipe and to th e Kelly.
Standpipe pressure is the point where the fluid pr essure is measured when
the fluid is entering the well.
Drill string & bit The mud pump moves the mud down the drill st ring to the bit. At the bit the
mud goes thr ough the nozzles. The mud cleans the cuttin gs around the bit.
Annulus Mud is transports th e cuttings up in th e annulus, first in the open holeannulus and then in the cased section of t he annulus.
Flow line Mud goes through the flow line /return line to the shale shaker.
Shale shaker The shale shaker has screen that removes cutting and th e mud falls into t he
mud tanks where the mud tanks can pump it up again for next circ ulation cycle.
Mud tanks
Centrifuge Shale shaker The mud pass
mesh sieves with a
certain size
200 mesh =
200 holes per in2
De-Sander
De-Gasser
Removes gas from
the mud
A hydrocyclone that
remove larger particles
in the mud with a
centrifugal force
(remove particles
larger than 40 microns)
De-Silter
Removes particles in
the size range of 2-5
microns
A hydrocyclone like the
de-sander but with
smaller cones (remove
particles larger than 20
microns)
Suction mud tank
Where the pump take
the mud to be
circulated in the hole
Mud pump
mponents of the Mudks
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Three main types of base fluids for drilling
Water based Fresh water, seaw ater, salt water
etc.
Oil based
NADF (Non Aqueous
Drilling Fluids)
Diesel, high on aromatics
Mineral oil
Synthetics, low on aromatics
Air or gas
based
Air, n it rogen, mis t, foam.
Functions of drilling fluids
Remove cuttings
Cool, lubricate, and lower friction for bit and
drill string
Prevent formation fluids from entering well
Keep wellbore walls from collapsing
Create filter cake in permeable formation to
prevent wellbore walls from caving in
Maintain stability of open hole – chemicallye.g. shale swelling
Transmit information from tools
Create weight/torque on bit
Power down hole directional tools to drilldirectional wells
Functions Desired properties
Keep cutting in suspension when
tripping
Clean bit
Low friction between drill string and
hole
Be as non damaging as possible to
producing formations
Be as environmentally friendly as
possible
Be pumpable at high densities
Be stable at high temperatures andpressures
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Laminar Flow
• Rheological Models
• Newtonian
• Bingham Plastic
• Power-Law
• Herschel-Bulkley
• Rotational Viscometer
• Laminar Flow in Wellbore
Laminar Flow of Newtonian Fluids
vF
large t
Fv
v
Fluid initially at restUpper plate set in
motion
Velocity build up
in unsteady flow
Final velocity
distribution in
steady flow
L
time<0 time = 0
small t
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Newtonian Fluid Model
Fluid Shear stress = viscosity * shear rate
A
F
L
V
vF
Large t
Final velocity
distribution in
steady flow
5 5 2
210 10 /F dyne N g cm s
A cm
Newtonian Fluid Model
In a Newtonian fluid the shear stress is directly proportional to the
shear rate (in laminar flow):
i.e.,
The constant of proportionality, is the viscosity of the fluid and
is independent of shear rate.
sec
12
cm
dyne .
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Bingham Plastic Model
Bingham Plastic Model
-if
-if 0
if
yyp
yy
yyp
and y (yield point) are often expressed in
lb/100 sq.ft
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Apparent Viscosi ty
Is not constant for a pseudoplastic fluid
The apparent viscosity decreases with increasing shear
rate
(for a power-law fluid)
(and also for a
Bingham Plastic fluid)
Rheological Models
1. Newtonian Fluid:
2. Bingham Plastic Fluid:
rateshear
viscosityabsolute
stressshear
*)( p y
viscosity plastic pointyield
p
y
What if y
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3. Power Law Fluid:
• When n = 1, fluid is Newtonian and K = m
• We shall use power-law model(s) to calculate pressure losses
(mostly).
n
)(K
K = consistency index
n = flow behavior index
Rheological Models
Typical Drilling Fluid Vs. Newtonian, Bingham and Power Law
Fluids
(Plotted on linear paper)
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Figure 3.6Rotating
Viscometer
Rheometer
We
determine
rheological
properties
of drilling
fluids in
this device
Infinite
parallel
plates
Rheometer (Rotational Viscometer)
Shear Stress = Dial Reading
Shear Rate = Sleeve RPM
)(f BOB
sleeve
fluid
RateShear the(GAMMA),of value
theondependsStressShear the),TAU(
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Example
A rotational viscometer containing a Bingham plastic fluid gives a dial
reading of 12 at a rotor speed of 300 RPM and a dial reading of 20 at arotor speed of 600 RPM
Compute plastic viscosity and yield point
12-20
300600 p
cp8 p
= 20
= 12
Example
8-12
p300y
2y ftlbf/1004
= 20
= 12
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Rotational Viscometer, Power-Law Model
Example: A rotational viscometer containing a non-Newtonianfluid gives a dial reading of 12 at 300 RPM and 20 at 600 RPM.
Assuming power-law flu id, calculate the flow behavior index and the
consistency index.
Example
cpeq.67.61511
12*510
511
510
7370.0
12
20 log322.3log322.3
7372.0
300
300
600
nK
n
n
= 20
= 12
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Gel Strength
0 300 600
= shear stress when fluid movement begins
τ
γ
τ y
RPM
Actual
readings of τ y
The yield strength, extrapolated from
the 300 and 600 RPM readings is not a
good representation of the gel strength
of the fluid
Gel strength may be measured by
turning the rotor at a low speed and
noting the dial reading at which the gel
structure is broken (usually at 3 RPM)
Gel Strength
2ft100/lbf
The gel strength is the maximum dial reading when theviscometer is started at 3 rpm.
g = max,3
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Just a reminder for this week
• HW 1 due tomorrow - Friday.• HW 2 will be posted today and due next Thursday.
• Lab 1 Due in two weeks! Note! follow the lab report
format.
• Remember and register your clickers this week.
• Next week no lab (Labor day), The following weeks the lab
will be in McNutt 115 drilling fluids lab.