Cementing Design

Oilwell cementing is the process

of mixing a slurry made up of
cement/additives and water.

It is pumped through the

WHAT IS casing into the annulus
OILWELL between the casing and the
CEMENTING drilled hole.
Cement plugs may also set in
the wellbore to isolate zones
e.g. loss zones, high pressure
zones, water bearing zones
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 One of the most important factors in
well completion is obtaining an
effective primary cement job. A
defective cement job will adversely
affect all remaining operations.
• There are two general classifications of
WHAT IS oil well cementing:
OILWELL • Primary Cementing
• supports the casing
CEMENTING • restricts the movement of formation fluids
behind the casing
• seals off zones of lost circulation
(fractured formation)
• protects the casing from shock loads during
the drilling of deeper sections
• protects casing from corrosion

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 Primary Cementing

Steel
Casing

Borehole

Cement

Steel Liner

4
 Secondary or remedial cementing
• Isolation squeeze
• Cement slurry is circulated into the
annulus
through perforations.
• Supplementing a faulty primary job
WHAT IS • Extending the casing protection
OILWELL above the cement top
• Plug back cementing
CEMENTING • The hole is plugged by
cement.
• Abandonment of the hole
• Sidetracking the hole
• Seal off lost circulation
• Shutting off of water or
gas encroachment

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 • Squeeze cementing

• Squeeze cementing involves forcing

the cement slurry (under pressure)
into open holes or channels behind
WHAT IS the casing or into perforation
OILWELL tunnels.
CEMENTING • The operation can be
performed during drilling,
completion or workover
operations

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 NEW SLURRY

7
 • Oil well cement, properly placed, will
have permeabilities of less than 0.1 md
and a compressive strength in
excess of 300 psi.
• The key to a successful cement job
OIL is proper placement of the
WELL cement completely around the
CEMENT casing.
• Cement compositions can be
classified as:
• Neat: Pure cement with no additives that
affect the strength of the cement.
• Blended: Cement that contains additives/
chemicals that affect the strength, setting
time and/or flow properties of the final slurry.
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 • Oil field cements are “Portland”
cements which are a finely ground (<
100 microns) mixture of calcium
compounds
• Tricalcium silicate (C3S): The major compound
and is the principle strength producing
material. It is responsible for early strength
development (1-28 days).
Portland • Dicalcium silicate (C2S): This compound is a
Cement slow hydrating material that accounts for the
gradual gain in strength over an
extended period.
• Tricalcium aluminate (C3A): Promotes
rapid hydration and controls the initial set
and thickening time. High levels (>3%)
adversely affect resistance to sulfide
attack.
• Tetracalcium aluminoferrite (C4AF): Low
heat of
5/24/2023 hydration compound.
 • All classes of API cement are
manufactured in much the same way
from the same ingredients, however,
proportions and particle size are
adjusted to give the desired
properties.
• API cements are classified as Class A
API
through Class H.
CEMENT • API Class A and B cements
CLASS • Intended for use in wells from the surface to the depth
of 6000 ft and 16 - 70 deg C
• The recommended water to cement ratio according to
• API
APIClass
is C
• 0.46 by weight
Is a high (5.2
strength gal/sack)
cement and used for oil wells from
surface to a depth of 6000 ft (16 - 77 deg C temperature)

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 • API Class D, E and F
• As a basic and regarded as retarded cement
• Intended for use from surface up to 16,000
ft depth
• Premium cement because of high cost
• Resistant to surface water
API • The primary class used in the oil field is Class
CEMENT G (Oil Well cement). [52% C3S, 32% C2S, 3%
C3A,
CLASS 12% C4AF, 3.2% CaSO4]
• On occasion Class C (High Early Strength) will
be utilized when rapid strength development is
required. [58% C3S, 16% C2S, 8% C3A, 8% C4AF,
4.1% CaSO4]

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Oil Well &
Construction Cements
• The principal differences between
construction and oil well
cements are that:
• No aggregate is added to the
oil well cements.
• Large volumes of water are
used in oil well cements in
order to permit the cement
slurry to be pumped.
 • The primary factors affecting slurry
quality and properties are:
• The composition of the cement
• Class and additives/chemicals
• The quality of the mix water
• Must be free of organic
CEMENT material
QUALITY • Must not have adverse
chemicals
• Should be fresh water
• The quantity of mix water
determines
• Slurry density and compressive strength
(reducing amount of mix water increases these
values)
• Slurry viscosity (less mix water increases
viscosity)
5/24/2023 • Pumpability time (less mix water decreases time)
 • There is a minimum amount of mix water required
to promote proper hydration of the cement
slurry, however, the “free-water” content of the
slurry should be kept below 1% (0 is preferred).
Too much free water will lower compressive
CEMENT strength and cause “flash set” through
QUALITY dehydration by excessive fluid loss.
• The recommended water to cement ratio according
to API for class G cement is 44% (5 gal/sack).
This value can be modified according to the
additives used or for density control.

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 Low viscosity over a sufficient period.

Sufficient strength within a reasonably short time in

order that the waiting-on-cement time (WOC) can
be kept to a minimum. The strength must be
sufficient to avoid mechanical failure under prevailing
downhole static and dynamic loads.

Cement Effective seal between the casing and the

formation.
Requirements
Impermeable that fluids cannot flow through it when it
has set.

Chemically inert to any formations or fluids with which

it may come into contact.

Stable enough for the length of time it will be in

use, which may be many years.
 • Compressive strength: Strength developed by the
CEMENT cement slurry once it starts to hydrate.
Compressive strength of neat cement continues to
SLURRY develop over a period of weeks (will increase until
PROPERTIES hydration is 100% complete). Generally will be in
the range of 1,000 to 4,000 psi depending on
temperature.

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6
 • Thickening time: The time it takes for internal gel strength
to attain the point (100 Poises) at which the slurry is no
longer pumpable (pumpability time).
• The higher the temperature the shorter the thickening
time.
• The higher the pressure the shorter the thickening time.
Thickening • Water loss accelerates the thickening process
time • Periods of non circulation will shorten the thickening
time rate: eddies and currents resulting from
• Pumping
turbulent
flow increases the thickening time.
• Amount of cement components that hydrate rapidly
(C3A, C3S).
• Fineness to which the clinker is ground.
 • In oil well drilling the cement bulk
surrounding the casing is subjected to
the following stresses:
• Static stress: shear stresses due to the
dead weight of the pipes;
Strength-time compressive stresses due to the action
of fluids and formations.
requirements
• Dynamic stresses resulting from the drilling
operation, specially the vibrations of the
drill string.
• To withstand these stresses a
compressive strength of the order
of 500 psi , after 24 hours period, is
needed.
 • Ordinary cements when they are
completely hardened, fracture excessively
when perforated.
• Low strength cements are usually less
Perforating brittle and have less tendency to
shatter upon perforating.
qualities
• Shattering of cement is not desired when
perforating near an OWC or OGC.
• Additives such as bentonite, pozzolan
and latex increase the ductility of set
cement.
 • Set cement could be penetrated by
corrosive liquids (especially those
containing CO2 or SO2).
• Cement corrosion decreases the final
Corrosion compressive strength render the
resistance cement more permeable.
• Reduction of the hardening time
improves the cements' resistance to
corrosion by corrosive fluids.
 • For clean surfaces (rock or metal) the
bond increases with time and moderate
temperatures.
• Mud cake and dirty casing surfaces
Bond reduce markedly the bond between
requirements casing (or rocks ) and cement.
• Additives such as salt and fine sand
increases the bond between casing
and the set cement.
 • Controls filtration rate especially during
squeeze jobs to prevent premature
setting:
Low Water • Diacel LWL
Loss Slurries • Halad 9 (Halliburton)
• Halad 11 (Halliburton)
• Flac (Dow Chemicals)
• Liquid latex
 • Granular, Fibrous or Flake forms of:
• Nut Shells and 2. Cellophane
Lost
Circulation • These materials must not contain any
substances soluble in water that
Materials would affect thickening times.
 • Set time: The time it takes the slurry to develop
sufficient strength to support the column of
cement (± 50 psi).
• Free water: Water that is not tied up in the
hydration process (should be less than 1%,
preferably zero).
CEMENT • Viscosity: The viscosity should be kept as low as
SLURRY possible to promote better filter cake removal
and good bonding.
PROPERTIES • Density: Ranges from 11 to 18.5 ppg. The higher
the density the higher the ultimate compressive
strength (assuming sufficient water for proper
hydration).
• Sulfate resistance: The higher the C3A the lower
the sulfate resistance as this compound reacts
with the sulfates to form calcium sulfoaluminate
crystals (large) which results in cracking.
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 • Permeability: In order to provide good
isolation the cement must have a very
low permeability when set.
• Cement bond: In order to provide good
isolation the cement must have good
bond to both the formation and casing.
CEMENT • Heat of Hydration: The heat generated
SLURRY during the hydration process. This can
PROPERTIES be quite high and if combined with
high BHT can cause flash sets.
• Flash set: The slurry sets in a much
shorter time than predicted. This
can be due to dehydration of the
slurry (high fluid loss) or to high
BHT/BHP.

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 Oil well cement slurries usually
contain additives to modify basic
Additives can:
properties.
• Vary slurry density
• Increase or decrease strength
CEMENT • Accelerate or retard setting time
ADDITIVE • Control fluid loss
S • Reduce slurry viscosity
• Bridge off loss circulation
• Improve economics
Many additives will affect more than
one property of the cement slurry.

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 • Accelerators: Additives to reduce the thickening
time and set the cement faster by accelerating the
hydration of chemical compound of cement.
• CaCl2 used in concentrations of ½ to 3%, above 3% it
can cause a flash set.
• Seawater acts as accelerator
• Retarders: Additives that lengthen the
thickening time of the slurry.
CEMENT • Most common are lignosulfonates.
ADDITIVE  Cellulose and sugar derivatives
S  Most retarders also act as fluid loss control agents
and dispersants.
 NaCl in concentrations below 2.5%, high values act as
a retarder.
 Calcium lignosulphate, pozzolan and CMHEC are
considered the most common retarders.

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 • Extra water: Causes the particles to
separate and settle out.
• Bentonite: For each 1% by weight add
extra water 3 to 5% by weight.
Lightweight • Diatomaceous Earth: Similar effects to gel,
less strength reduction.
Additives
• Perlite: Ground volcanic lava.
• Gilzonite: 25 to 50% with cement.
• Pozzolan: 50-50 with cement gives greater
strength and better sulphate resistance.
 • Weighting agents: Additives that increase
the density of the cement slurry.
• The weight of cement slurries can be
increased by adding barite, illmenite or
hematite
CEMENT • Bridging agents: Material added to the cement
ADDITIVE to prevent slurry losses to the formation.
• Many standard LC materials can be used to
S help the slurry bridge off at the wellbore wall.
Normally only fine grades of LCM will be used
to prevent adverse affects on other slurry
properties. [mica, nut hulls, etc].

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9
 Heavyweight Additives

Barites Hematite Ottowa Sand

(S.G. 4.3 ): (S.G. (S.G. 2.1):
35.03 5.05): 17.51 ppg
ppg 42.12
ppg
 • Fluid loss: Additives that lower the
amount of filtrate lost to the
formation.
• Normally lignosulfonate compounds.
• Maybe HEC or Diacel.
CEMENT Excessive fluid loss, as the slurry is placed,
can damage water sensitive production
ADDITIVE zones.
• Turbulence inducers (dispersants): Additives
S that aid in attaining turbulent flow behavior.
• Most common is lignosulfonate compounds
• Allows a reduction in placement rate while
maintaining a turbulent flow regime. Turbulent
flow is desired as it gives better cleaning of
filter cake.

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 • There are many products that can be
used to make the slurry more
economical. These are materials that
can be blended with the cement
and are less costly than the cement.
• Bentonite, fly ash and pozolan can be
CEMENT used
ADDITIVE to “extend” cement slurries.
S • In low concentrations fly ash and
pozolan will not affect the ultimate
strength of the final product.
• Bentonite will lower the
compressive strength.

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 • It must be remembered that most
additives will affect more than one
slurry property so care must be taken
CEMENT when combining additives with the slurry.
ADDITIVE • For this reason lab tests must be run on
S the actual make up water and the
specific blend of additives and
cement to be used.

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Additives
MANUFACTURE OF
CEMENTS
• Cement is made of
Limestone and clay or shale
mixed in the right
proportions.
• Each run may be slightly
different due to impurities
• Cement is heated in a rotary
kiln to 2600 to 2800 F
MANUFACTURE OF
CEMENTS
• What comes out of the kiln
is called clinker.
• The resultant clinker is
mixed with
1.5 to 3% by weight Gypsum
(CaSO4 - 2H2O) which controls
rate of settling and hardening. •
The resultant is Portland
Cement.
 • High Temperature Cements: High
temperature can effect the strength of
cement. Therefore the following
Special additives may be used:
Cements • Add 30% silica flour - prevents
strength retrogression and
improves bonding. "Pozmix 140"
(Halliburton) - pozzolans-
Iime+chemicals.
 • A portland cement to which a surface
active agent is added, it is designed
for mixing with diesel oil.
Diesel • It will not set and harden until it
oil comes in
cements contact with water.
• It is used for shutting off water
production from the completion interval
of a well.
 • Perlite cements are prepared by
adding perlite to ordinary portland.
• Perlite is a light volcanic ore, when
heated to fusion it gives rise to a
Perlite very low density product (13 lb/ft3).
cements • Bentonite is usually added to perlite
cement slurries to disperse perlite
more uniformly through the mixture.
• Perlite cements are expensive.
 • It is composed of latex, cement and
water.
• It is used for plug back jobs for
Latex cement water exclusion.
• It is especially resistant to oil and
mud contamination.
• It gives a high strength bond with
casing and rocks.
 • Pozzolan (siliceous rocks of volcanic
origin) is added to portland
cements or used with lime (lime
pozzolan cement).
Pozzolanic • Pozzolan cements have
cements higher pumpability times
than most conventional
cements.
• Pozzolanic cements are light,
ductile and they are proved to
be satisfactory deep well
cements.
 Cement by Casing Types & Coverage
Casing Top of Cement Coverage
Conductor / 1. Surface or sea floor 1. Exploration wells shall only be cemented to seabed level to facilitate
Surface cutting and retrieval of casings.
On Development wells to reduce
corrosion:
1. Annular space between the
casing and formation shall be
filled back to
surface.
2. If no cement returns observed,
a grout job shall be performed.
Intermediate 1. 500ft above all 1. If zonal isolation is required, the cement shall fill the annular
hydrocarbon and space between casing and hole to at least 500ft above the zones
abnormal pressure to be isolated.
zones 2. If zonal isolation is not required, the cement shall fill the annular
2. 500ft above the space
previous casing between the casing and hole to at least 500ft above the previous casing
shoe. shoe.
Production 1. 500ft above the 1. The cement height shall cover at least 1/3 of the total measured
uppermost producible length of the production casing to provide casing stability.
hydrocarbon zone or
2. 500ft above the
previous casing shoe
depth.
Liner 1. Top of liner lap 1. Liner strings shall generally be cemented from the shoe to the top of
5/24/2023 the liner lap. 42
43
44
Cement
Equipmen
t
Cement Head is a device fitted to the top joint of a casing
string to hold a cement plugs before they are pumped down
the casing during the cementing operation. In most
operations, a bottom plug is launched before the spacer or
cement slurry. The top plug is released from the cement
head after the spacer fluid. Most cement heads can hold
both the top and bottom plugs.

Cement Head
Cement Equipment

• Common cementing equipment

includes
• •Float shoe
• •Float collar
• •Centralizers
• •Cementing head
• •Scratchers
• •Well-bore Wipers
• •Top and Bottom plugs
47
48
Well Cleaners

• These are used to assist in

clearing the mud cake
when running the
pipe by reciprocation or
rotation.
• There are two types:
 Scratchers
 Well-bore Wipers
 • This is more critical in deviated wells than
in straight holes.
• We must not use too many as we will be
unable to
get the casing into the ground.
• Frictional forces will be greater than the
pipe weight.
Effective
Centralization
 Wiper
• Plugs
Wiper plugs are equipped with rubber-
cupped fins which wipe mud from the
walls of the casing ahead of the cement
and clean the walls of casing behind the
slurry.
• The bottom plug is launched ahead of the
cement slurry to minimize contamination
by fluids inside the casing prior to
cementing.
• A diaphragm in the plug body ruptures
to allow the cement slurry to pass
through after the plug reaches the
landing collar.
• The top plug has a solid body that
provides positive indication of contact
with the landing collar and bottom plug
through an increase in pump pressure. 5
1
 • To prevent contamination & washes, plugs are
often pumped ahead of slurry.
• The washing water and chemicals assist in cleaning
the wellbore as well as acting as a spacer.
• The first wiper plug cleans the inside of the casing and
lands in the float collar, the diaphragm bursts and
allows the cement to be pumped out of the casing.
Cement Job & • The bottom plug separates the cement from the
displacing mud and signals displacement complete,
Contamination when it 'bumps' on the first plug.
• The casing, from the float to the shoe will be full of
cement, if there is any contaminated cement collected
by the bottom plug, it will be inside this portion.
• The cement around the shoe joint must be of the
best quality.
• There are ball valves on springs in both float and
shoe,
which do not allow the cement to back flow.
53
 • After cement hardens, releasing pressure
on the casing permits it to contract so
that the bond with the cement may be
Considerations loosened.
after • Release of pressure on the casing before
cementing the cement sets eliminates this problem.
• Pressure is made to bleed off if the back
pressure valve in the casing string is
holding satisfactorily.
 •Long term hydraulic isolation in
Deepwater cementing operations:
• Strict slurry density control at
surface and downhole
conditions
Deepwater • Adequate rheology for
Cementing optimal mud displacement
Objectives • Fast gel and compressive
strength development
• Minimal shrinkage and
low permeability
• Engineered set cement mechanical
properties
 Surface casing jobs – Zonal isolation
from shallow gas or water ingression,
quick compressive strengths in lower
temperatures, riser margins, large
annular volumes.

Unique Production casing jobs – Fluid migration

due to poor mud displacement, strength
Deepwater retrogression, pressure limitations of
cementing casing equipment, highly deviated
Issues casing equipment and APB.
Common DW cementing concerns –
Large annular volumes, lost circulation,
potential flow zones, hole stability, APB,
salt entry / exit, volume ratio of shoe
track and rat hole.
 • Efficient mud removal helps to achieve zonal
isolation, strong bonding of cement with casing
and formation walls, and structural support for the
well.
• Poor mud displacements lead to critical problems
like contamination of fresh water bearing zones
Fluid and leakage to the surface.
• Elongated and unstable mud cement interfaces
migration due are usually associated with channelling through the
to poor mud interface, excessive mixing, and cement
contamination, which can lead to poor or even
displacement failed cementing jobs.
• A major objectives of cementing is to provide
zonal isolation and restrict the fluid flow between
the formations which can happen only if the
drilling fluid is effectively removed from the
annulus. Otherwise, it can cause different problems
such as interzonal communication, unwanted
production, annular gas migration, and casing
corrosion.
 • Strength retrogression of set Portland cement
at elevated temperatures, (say > 230°F) is
believed to be due to the formation of a
variety of crystalline phases at the expense
of amorphous calcium silicate hydrate
Cement phase.
strength • Ground quartz silica is typically added to
prevent the strength retrogression. The
retrogression amount of silica needed to prevent strength
retrogression depends on temperature.
• Calcium hydroxide that is generated from
cement hydration reacts with silica in
pozzolanic reactions to generate amorphous
calcium silicate hydrate.
 • Casing and cementing operations in salt
zones can pose particular challenges.
• Salt has effect of salt dissolution on cement-
slurry properties
Cementing in • There are dangers presented by salt creep to
the integrity of the well and the need to plan
Salt for contingencies for potential zones of
overpressure or lost circulation.
• Common in major subsalt basins of the
world, including the North Sea, Brazil
and the Gulf of Mexico.
APB Issues

• APB occurs when the high temperature

hydrocarbons travel up and heat up
the well.
• In some cases, the pressure can
become high enough to collapse
casing strings.
• A number of design features to
manage annular pressures or mitigate
the risks of casing collapse exist.
• These include rupture disks,
compressible fluids in the annular
space, and insulated production
tubing.
 • When it is necessary to cement pipe
with diameters of 16 inch, 18 inch, 20
inch, or larger, tubing or drill pipe is
commonly used as an inner string in
the placement of the cement.
• The tubing, or drill string, is stabbed into
Inner String a specially designed float collar or
guide shoe.
Cementing • This procedure reduces the cementing
time and the volume required to
pump the cementing plug.
• It also avoids having to displace a
large volume of cement that would be
in the large casing if channeling
should occur.
 Large-Hole
Cementing

Normal
Displacement
Method

• Down the inside of the Csg.

• Use two wiper plugs
• Takes a long time . . .
• Large surface area
exposed to the cmt.
62
 Large-Hole
Cementing

Inner String
Cementing

• Down the inside of the

DP
• Use top wiper plug
• Stab-in adapter
63 • Much shorter displ. time
 Deep Well
Liner
Cementing
• Deep wells usually start with 20 to 30-inch conductor
casing and are ultimately completed with 5, 5-1/2 or
7- inch liners.
• In some of the deep wells, it is common to set two liners
(a drilling liner & a production liner) before reaching the
ultimate drilling objective.
• The wear and tear on the intermediate liner during
drilling often requires the setting of a tie-back string
before the well is completed.
• The tie-back string stabilizes and reinforces the
intermediate liner and intermediate casing, which
may have been weakened during the drilling process.
 • This technique is used for cementing two
or more separate sections behind a
casing string. Used for the following
reasons:
 When a long cement column could not
Stage be used without breakdown of the
Cementing formation behind the string.
 When it is necessary to reduce the
pumping pressure at the surface,
especially in cementing deep wells.
 When slurries of different compositions
are used for cementing distinct sections.
 Multi-Stage
Cementing

 Pump first stage

 Displace cmt.
 Open stage tool
 Pump second
stage

 Displace cmt
 Last plug closes
66 tool
 •There are a number of things we can do to increase
the odds of getting a good cement job
• Centralization of the casing
• Pipe movement - rotation and/or reciprocation
Cement • Drilling fluid condition

Job
• Hole conditions
• Displacement velocity
• Spacer fluids
• Mud - cement density differences
• Contact time
 • In the past, cement jobs have been
assumed to be good, unless there
was immediate evidence to the
contrary.
• Now, however, cement evaluation logs are
Evaluation of becoming more and more prevalent.
Cement Job • CBL (cement bond log) is normally run
on wireline after drilling the next hole
section.
• It might be necessary to perforate and
squeeze if these logs show that the
primary job is not all that it might be.
 • Turbulent flow gives the best cleaning or
scouring effect.
• The faster the rate of flow, the nearer to
this turbulence we are likely to be.
• If the pipe is not concentric in the
wellbore, turbulent flow
Flow is difficult to attain all around the pipe
and the cement will tend to
Patterns channel.
• Laminar flow should be avoided since
it promotes channeling
• Some cement studies touted plug flow
while some indicated that turbulent
flow was better.
Cementing
Program
 Surface casing jobs – Zonal isolation
from shallow gas or water ingression,
quick compressive strengths in lower
temperatures, riser margins, large
annular volumes.

Unique Production casing jobs – Fluid migration

due to poor mud displacement, strength
Deepwater retrogression, pressure limitations of
cementing casing equipment, highly deviated
Issues casing equipment and APB.
Common DW cementing concerns –
Large annular volumes, lost circulation,
potential flow zones, hole stability, APB,
salt entry / exit, volume ratio of shoe
track and rat hole.
Deepwater Cementing
Challenges
• Shallow water / gas flow: High flow rates can be
cause to washout craters, large enough to seriously
jeopardize well integrity. If not properly handled, this
can lead to high water flows through the cemented
annulus of the shallow surface casing.
• Low seabed temperature: For 20” and 30” surface
casing sea bed temperatures can range between 4 –
12 deg C, depending upon the water depth. The slurry
properties like thickening time, transition time, time to
achieve early compressive strength and rheology of
cement slurry have a retarding effect and tends to
elongate the above parameters.
• Low Fracture gradient : The fracture gradient in deep
water wells are very low. Consequently, low weight
cement slurries are used for surface casing jobs (30”
and 20”).
 Slurry design should include following considerations:
• Use of Low density cement slurry / optimized lightweight
cementing system.
• Cement slurry should have High gel strength and less
transition time (critical hydration period).
• Cement slurry should have additives to control gas
Surface migration.
casing • Cement slurry should have sufficient early CS
cementing in /controlled fluid
loss and nil free water.
DW Microspheres or hollow spheres (glass or ceramic spheres),
when added to the cement system, allow reduction of the
cement density without additional mix water, thereby improving
the compressive strength development properties at low
temperature. The typical range of slurry density with the
application of microspheres is 8.5 to 14 ppg. The performance
properties can be adjusted with accelerators and anti-gas
migration additives.
 • Another way to reduce the slurry density is to add compressed
nitrogen gas to the cement while mixing.
• The gas in the cement will maintain a matrix pressure in the slurry
which
shall exceed the pore pressure of the potential flow zone.
• Foam cements provide requisite structural support to first casing against
anticipated well loads.
• Prevents migration up the annulus after cementing. Shallow flows (less
than about 5000 ft. BML) are the most difficult to control and foam
cements have proved to be most successful.
Foam • Higher shear bond strengths provide an effective seal between the
cement / pipe / wellbore surfaces
Cementing • Greater ductility / Better early compressive strength development /
Higher ultimate strength
• Flexibility to alter slurry design throughout the cementing
operation
• Good fluid-loss control properties at the low densities and temperatures
encountered in deep-water environments / Better mud removal
characteristics.
 EXAMPLE CALCULATIONS

Annular Volume = (DH^2 – DCSG^2)/1029.4

bbl/ft
• Given :
• Hole = 13” (after
• Size
Casing Sizewashout)
= 9.625”
• Hole Length = 3,000
ft.
• Excess 10%
•=Calculate volume of cement needed for the above
well.

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 EXAMPLE CALCULATIONS

• Ann. Volume = (DH^2 – DCSG^2)/1029.4

• bbl/ft = (13^2 –
• 9.625^2)/1029.4
• = (169 – 92.64)/1029.4
= 0.0742 bbl/ft
• Total Volume = Ann. Volume * Length +
• excess = .0742*3000 +
• 0.0742*3000*0.1
• = 222.6 + 22.3 bbls
= 244.9 bbls.

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Example 2

• Well is drilled with 8.5 inch bit to 9,015 MD/8,505 TVD with oil
based mud (9.5 ppg). Estimated hole sized based on an open hole
log is 8.6 inch. Previous casing size is 9-5/8” and its shoe is at 6,500
MD/5000’TVD. Plan to run 7” casing and planned shoe depth at
9,000’MD/8,500’TVD. There is one float collar at 8960’MD/8470’
TVD. Top of cement is 2000 ft above 9-5/8” casing. Spacer volume
is from top of cement to surface.
• Casing information:
• 7” casing ID = 6.185”; 9-5/8” casing ID = 8.85”. Use hole
size
measured from the open hole log to determine cement volume.

• Determine the following: Cement volume; Spacer volume;

Displace volume.
Solution – Example 2

• Determination of Cement volume:

• Total cement volume = cement in the annulus between open hole and 7” casing + cement in annulus between 9-5/8” casing and 7” casing
+ cement in shoe track.
• Cement in the annulus between open hole and 7” casing
• Annular capacity between open hole and 7” casing = (8.62-72) ÷ 1029.4 = 0.02425 bbl/ft
• Length from 7” casing shoe to 9-5/8” casing shoe = 9000 – 6500 = 2500 ft
• Cement in the annulus between open hole and 7” casing = 0.02425×2500 = 60.6 bbl
• Cement in annulus between 9-5/8” casing and 7” casing
• Annular capacity between 9-5/8” casing and 7” casing = (8.852-72) ÷ 1029.4 = 0.02849 bbl/ft
• Length of cement inside 7” casing = 2000 ft
• Cement in annulus between 9-5/8” casing and 7” casing = 0.02849 x 2000 = 57 bbl
• Cement in shoe track
• Capacity of 7” casing = 6.1852 ÷ 1029.4 = 0.03716 bbl/ft
• Shoe track length = 40 ft
• Cement in shoe track = 40 x 0.03716 = 1.5 bbl
• Total Cement Volume
• Total cement = 60.6 + 57 + 1.5 = 119.1 bbl
 Solution – Example
• 2
Determine space volume
• As per the cement program, spacer will be at surface.
• Spacer volume = Annular capacity between 9-5/8” casing and 7” casing x length of spacer
• Annular capacity between 9-5/8” casing and 7” casing = (8.852-72) ÷ 1029.4 = 0.02849 bbl/ft
• Length of spacer = volume annulus to TOC
• TOC 2000 ft inside casing shoe = 6,500 – 2,000 = 4,500 ft
• Spacer volume = 0.02849 x 4,500 = 128.2 bbl
• Determine displace volume
• The displacement volume is from surface to the float collar where the top plug will sit on.
• Displacement volume = Capacity of 7” casing x Length to the float collar
• Capacity of 7” casing = 6.1852 ÷ 1029.4 = 0.03716 bbl/ft
• Length to the float collar = 8,960 ft
• Displacement volume = 0.03716 x 8960 = 333 bbl
• Conclusion for this cement calculation
• Cement volume = 119.1 bbl
• Spacer volume = 128.2 bbl
• Displace volume = 333 bbl
What is a Sack of Cement & Cement Yield

• In oilfield, a sack refers the amount of cement that occupies a bulk

volume of 1.0 ft3. For most portland cement, including API classes
of cement, a sack weighs 94 pounds.
• The sack is the basis for slurry design calculations and is often
abbreviated as sk.
• The volume of slurry obtained when one sack of cement is mixed with
the desired amount of water and other additives, usually given in units
of m 3 /kg or ft 3 /sk (sack).
 EXAMPLE CALCULATIONS

• Based on the above volume, calculate the cement

requirements
• Given:
• Cement yield = 1.15 ft3/sx.
• 1.0 bbl = 5.615 ft3 = 42 gal
• Cement volume = 244.9 bbls (from previous example) = 1375
ft3.
• No of Cement sacks = Slurry volume / slurry yield
• No of sacks = Volume / Yield = 1375 / 1.15 = 1,196
sacks.

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 EXAMPLE CALCULATIONS

• Based on the above saks, calculate the additive requirements

• for:
Water = 5 gal/sx
• Retarder = 0.5
• Fluid gal/sx
• Loss = 0.9 = Cement sacks * Additive
Additive Volume
gal/sx
concentration
• No of sacks = 1196 from previous example
• Water = 1,196 * 5 = 5980 gals = 142.4 bbls.
• Retarder = 1,196 * 0.5 = 598 gal.
• Fluid Loss = 1,196 *0.9 = 1,076.4 gal.

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 THANK
YOU OPEN
FOR
QUESTIONS
Disclaimer: The presentation is a gist of authors Industry
experience, class room lectures, textbook material and
Deepwater Course manuals and research papers. This is
a presentation made for Seniors in Petroleum Engineering
for learning purposes and no claim whatsoever is made
by author to own or independently create the material.