Cementation jobs

1. CEMENTATION JOBS

ASSIGNMENT
SABA SAIF
01-161102-065
BS-GEOPHYSICS-7

2. Table of Contents
INTRODUCTION ................................................................................................... 2
OBJECTIVE: .......................................................................................................... 2
CEMENTING: ........................................................................................................ 3
HOW DOES CEMENTING WORK? .................................................................... 4
PREPARING THE CEMENT: .............................................................................................................. 5
CEMENTING THE WELL: .................................................................................................................. 6
PRIMARY CEMENTING: ..................................................................................... 7
PRIMARY CEMENTING TECHNIQUES: .............................................................................................. 8
API & ISO CLASSIFICATION SYSTEM: ........................................................... 8
SINGLE STAGE CEMENTING: ........................................................................... 8
ZONAL ISOLATION: ............................................................................................ 9
STAGE CEMENTING: .......................................................................................... 9
CEMENT ADDITIVES: ....................................................................................... 11
ACCELERATORS ............................................................................................................................ 11
RETARDERS: ................................................................................................................................. 12
FLUID LOSS ADDITIVES:................................................................................................................. 12
DISPERSANTS: .............................................................................................................................. 12
EXTENDERS: ................................................................................................................................. 13
HEAVY WEIGHT ADDITIVES: .......................................................................................................... 13
CONCLUSIONS: .................................................................................................. 13
REFERENCES:..................................................................................................... 14
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3. CEMENTATION JOBS
INTRODUCTION:
Cementing is performed by circulating
a cement slurry through the inside of the
casing and out into the annulus through
the casing shoe at the bottom of
the casing string. In order to precisely
place the cement slurry at a required
interval on the outside of the casing, a
plug is pumped with a displacement fluid
behind the cement slurry column, which
"bumps" in the casing shoe and prevents
further flow of fluid through the shoe.
This bump can be seen at surface as a
pressure spike at the cement pump. To
prevent the cement from flowing back
into the inside of the casing, a float
collar above the casing shoe acts as
a check valve and prevents fluid from
flowing up through the shoe from the
annulus.
Cement fills and seals the annulus
between the casing string and the drilled
hole. It has three general purposes:
 Zone isolation and segregation,
 Corrosion control, and
 Formation stability and pipe
strength improvement.
Cement forms an extremely
nearly impermeable seal from
slurry. The properties of the
slurry and its behavior depend
components and the additives
cement slurry.
strong,
a thin
cement
on the
in the
Figure: 1 Cementing Plugs
OBJECTIVE:
Cementing is one of the most critical steps in well completion. Well cementing
technology is the application of many scientific and engineering disciplines. The
objective of my assignment is to understand the concept of cementation and to learn
about the various cementing techniques being used by the E & P companies.
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4. CEMENTING:
After the casing string is run, the next
task is cementing the casing in place. An
oil-well cementing service company is
usually called in for this job although, as
when casing is run, the rig crew is
available to lend assistance.
Cementing service companies stock
various types of cement and have special
transport equipment to handle this
material in bulk. Bulk-cement storage and
handling equipment is moved out to the
rig, making it possible to mix large
quantities of cement at the site. The
cementing crew mixes the dry cement
Figure: 2 Well Cementing
with water, using a device called a jetmixing hopper. The dry cement is gradually added to the hopper, and a jet of water
thoroughly mixes with the cement to make a slurry (very thin water cement).
Special pumps pick up the cement slurry and send it up
to a valve called a cementing head (also called a plug
container) mounted on the topmost joint of casing that
is hanging in the mast or derrick a little above the rig
floor. Just before the cement slurry arrives, a rubber
plug (called the bottom plug) is released from the
cementing head and precedes the slurry down the
inside of the casing. The bottom plug stops or "seats"
in the float collar, but continued pressure from the
cement pumps open a passageway through the bottom
plug. Thus, the cement slurry passes through the
bottom plug and continues on down the casing. The
slurry then flows out through the opening in the guide
shoe and starts up the annular space between the
outside of the casing and wall of the hole. Pumping
continues and the cement slurry fills the annular space.
A top plug, which is similar to the bottom plug except
that it is solid, is released as the last of the cement
slurry enters the casing. The top plug follows the
remaining slurry down the casing as a displacement
fluid (usually salt water or drilling mud) is pumped in
behind the top plug. Meanwhile, most of the cement
slurry flows out of the casing and into the annular
space. By the time the top plug seats on or "bumps" the
bottom plug in the float collar, which signals the
cementing pump operator to shut down the
pumps, the cement is only in the casing below the
Figure: 3 Cementing Plugs
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5. float collar and in the annular space. Most of the
casing is full of displacement fluid.
After the cement is run, a waiting time is allotted to allow the slurry to harden. This
period of time is referred to as waiting on cement or simply WOC.
After the cement hardens, tests may be run to ensure a good cement job, for cement is
very important. Cement supports the casing, so the cement should completely
surround the casing; this is where centralizers on the casing help. If the casing is
centered in the hole, a cement sheath should completely envelop the casing. Also,
cement seals off formations to prevent fluids from one formation migrating up or
down the hole and polluting the fluids in another formation. For example, cement can
protect a freshwater formation (that perhaps a nearby town is using as its drinking
water supply) from saltwater contamination. Further, cement protects the casing from
the corrosive effects that formation fluids (as salt water) may have on it.
HOW DOES CEMENTING WORK?
Part of the process of preparing a well for further drilling, production or
abandonment, cementing a well is the procedure of developing and pumping cement
into place in a wellbore.
Figure: 4 Onshore Cementing Operations and Equipment
Used for a number of different reasons, cementing protects and seals the wellbore.
Most commonly, cementing is used to permanently shut off water penetration into the
well. Part of the completion process of a prospective production well, cementing can
be used to seal the annulus after a casing string has been run in a wellbore.
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6. Additionally, cementing is used to seal a lost circulation zone, or an area where there
is a reduction or absence of flow within the well. In directional drilling, cementing is
used to plug an existing well, in order to run a directional well from that point. Also,
cementing is used to plug a well to abandon it.
Cementing is performed when the cement slurry is deployed into the well via pumps,
displacing the drilling fluids still located within the well, and replacing them with
cement. The cement slurry flows to the bottom of the wellbore through the casing,
which will eventually be the pipe through which the hydrocarbons flow to the surface.
From there it fills in the space between the casing and the actual wellbore, and
hardens. This creates a seal so that outside materials cannot enter the well flow, as
well as permanently positions the casing in place.
PREPARING THE CEMENT:
In preparing a well for cementing, it is important to establish the amount of cement
required for the job. Measuring the diameter of the borehole along its depth, using a
caliper log, does this. Utilizing both mechanical and sonic means, multifinger caliper
logs measure the diameter of the well at numerous locations simultaneously in order
to accommodate for irregularities in the wellbore diameter and determine the volume
of the open hole.
Additionally, the required physical properties of the cement are essential before
commencing cementing operations. The proper set cement is also determined,
including the density and viscosity of the material, before actually pumping the
cement into the hole.
Special mixers, including hydraulic jet
mixers, re-circulating mixers or batch mixers,
are used to combine dry cement with water to
create the wet cement, also known as slurry.
The cement used in the well cementing
process is Portland cement, and it is
calibrated with additives to form one of eight
different API classes of cement. Each is
employed for various situations.
Additives can include accelerators, which
shorten the setting time required for the
cement, as well as retarders, which do the
opposite and make the cement setting time
longer. In order to decrease or increase the
density of the cement, lightweight and
heavyweight additives are added. Additives
can be added to transform the compressive
Figure: 5 Cementing Techniques strength of the cement, as well as flow
properties and dehydration rates. Extenders can be used to expand the cement in an
effort to reduce the cost of cementing, and antifoam additives can be added to prevent
foaming within the well. In order to plug lost circulation zones, bridging materials are
added, as well.
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7. CEMENTING THE WELL:
After casing, or steel pipe, is run into the well, an L-shaped cementing head is fixed to
the top of the wellhead to receive the slurry from the pumps. Two wiper plugs, or
cementing plugs, that sweep the inside of the casing and prevent mixing: the bottom
plug and the top plug.
Keeping the drilling fluids from mixing with the cement slurry, the bottom plug is
introduced into the well, and cement slurry is pumped into the well behind it. The
bottom plug is then caught just above the bottom of the wellbore by the float collar,
which functions as a one-way valve allowing the cement slurry to enter the well.
Then the pressure on the cement being pumped into the well is increased until a
diaphragm is broken within the bottom plug, permitting the slurry to flow through it
and up the outside of the casing string.
Figure: 6 Bottom and Top Plugs
After the proper volume of cement is pumped into the well, a top plug is pumped into
the casing pushing the remaining slurry through the bottom plug. Once the top plug
reaches the bottom plug, the pumps are turned off, and the cement is allowed to set.
The amount of time it takes cement to harden is called thickening time or pumpability
time. For setting wells at deep depths, under high temperature or pressure, as well as
in corrosive environments, special cements can be employed.
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8. PRIMARY CEMENTING:
Primary cementing is the first cementing operation performed after the casing has
been run in the hole. This is accomplished by pumping cement slurry down inside
casing and displaced it out into the annular space between the casing and the
borehole. The cement is then allowed to set before drilling is resumed or the well is
completed.
The main functions of primary cementation are:
 To bond and support the casing.
 To isolate the drinking water zone
 To keep the well safe for drilling oil & gas zones
 Protecting the casing from corrosion.
 To restrict fluid movements between formations.
 Protecting the casing from shock loads during drilling deeper.
 Sealing-off problematic zones.
 Last and the most important is Complete and durable zonal isolation for oil
and gas production.
Figure: 7 Primary Cementation
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9. PRIMARY CEMENTING TECHNIQUES:
Numbers of techniques are used for primary cementing. Following are the three most
commonly used techniques:
 Single stage cementation
 Multi stage cementation
 Liner cementation
API & ISO CLASSIFICATION SYSTEM:
The requirements for well cements (WC) are more rigorous than construction cements
(CC) .WC must perform over a wide range of temp and pressures and are exposed to
subterranean conditions that CC do not encounter.
Oil well cements are compositions variable concentrations of C3S2, C2S, C3A and
C4AF.
There are 8 classes of API-ISO Portland cement designated A-H
CLASS-A-ordinary Portland Cement.
CLASS-B-medium (MSR) to high (HSR) sulphate resistance Portland Cement.
CLASS-C- Portland Cement wit high early strength in O, MSR & HSR property.
CLASS-D/E/F-known as retarded cements by reducing fast hydrated phases (C3S and
C3A) with increase in particle size-rarely used.
CLASS-G/H- for use as basic Oil well Cement developed in response improved
technology in slurry acc /returd by chem means.
SINGLE STAGE CEMENTING:
Single stage cementing is most commonly used for primary cementing, where there is
no complication or lost circulation and where cement rise in the annulus can be
attained in one stage. The single stage primary cementing is normally accomplished
by pumping one batch of cement down the casing between two rubber plugs.
The bottom plug is placed in the casing, followed by cement slurry. When the batch
of cement has been pumped into the casing, a top plug is released the top plug is
pumped down until it lands on the top of float collar. Thus completing the cement job.
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10. ZONAL ISOLATION:
 Complete and durable zonal isolation is the foremost goal of the cement job
 During the life of a producing oil or gas well, quality of the cement job has a
direct impact on the economic longevity of the well.
 From starting of production to abandon the well, slurry design and placement
technique will effect the well productivity, both physically & economically
 If allowed to set undisturbed Portland cement system with 16-ppg density
usually exhibit very matrix permeability.
 During the production phase cement is subject to various severe conditions
that effect the longevity of the matrix permeability-termed called cracking
/Debonding is caused by thermal & pressure fluctuations- subsequently
cement integrity is lost resulting secondary cement job for isolation repair.
Figure: 8 Zonal Isolation
STAGE CEMENTING:
Stage cementing consist of placement of cement slurry first around the lower portion
of a casing string using conventional primary cementing technique and then
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11. cementing the successive upper stages through ports in the stage collar. Most stage
cementing is in two stages, although additional stages are possible. Cementation is
required to be done in two or more stages because of the following reasons:
 Down hole formation unable to support hydrostatic pressure exerted by a long
column of cement.
 Cement not required between widely separated intervals.
 When the volumes of cement cannot be handled with the limited cementing
equipment.
 To cement deep wells with high bottom hole temp, where cement slurries of
different thickening time for different stages can be used.
 For cementing of high-pressure gas zones and water producing horizons.
Figure: 9 Stage Cementing
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12. Figure: 10 Showing two-stage cementing of a casing string
The sequence of operation for two-stage cementation is shown in the figure above.
After first stage cementing has been performed in a conventional manner, an opening
bomb is dropped to land in the lower seat of the stage collar. By pressuring up (1200
to 1500 psi). The retaining pins are sheared, the sleeve moves down and the ports are
opened.
The well is then circulated to clear the ports and condition the mud. For cementing the
second stage, spacers and slurries are mixed as in any single stage job. The closing
plug is dropped after the slurry pumping and is displaced till it seat on the upper
sleeve in stage collar. After the plug has seated, a minimum of 1200-1500 psi above
the second stage displacing pressure is required to close the collar ports. And thus
completing the two stage cementing job.
CEMENT ADDITIVES:
ACCELERATORS
 Accelerating a slurry means shortening the Thickening Time or reducing the
time required to gain Compressive Strength or both.
 In general an in-organic material will act as an accelerator.
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13. Examples:
Calcium Chloride, Sodium Chloride, Sea water, potassium Chloride, Sodium
Silicate, Gypsum etc.
RETARDERS:
 A material that allows sufficient time for slurry placement by delaying the set
of the cement is called a retarder.
 In general, any organic material will retard the setting time of cement slurry.
Examples:
Calcium Lignosulfonates, Calcium sodium Lignosulfonates, Organic acids etc.
FLUID LOSS ADDITIVES:
 Reduces the rate at which filtrate is lost to a permeable formation.
 Works by viscosifying the mix water or by plugging the pore throat in the
filtrate cake with long polymer chains.
Examples:
 Organic polymers (Cellulose)
 Organic polymers (Dispersants)
 CMHEC.
DISPERSANTS:
 Also called friction reducers, these materials make cement slurries easier to
mix and pump.
 Act on surface charges of the cement grains.
 Secondary retardation
 Enhances fluid loss control.
Examples:
 Polynapthalene sulfonate (PNS),
 Non-lignosulfonate.
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14. EXTENDERS:
 Additives that reduce slurry density and increase slurry yield are called
extenders.
 Cement may be lightened to protect the weak formations or slurry yield may
be increased to reduce the cost.
Examples:
Water, Bentonite, Pozzolan, Gilsonite etc.
HEAVY WEIGHT ADDITIVES:
These are required to counter high formation pressures.
Common high-density materials are:
a) Hematite
b) Ilmenite
c) Barytes
CONCLUSIONS:
Cement forms an extremely strong, nearly impermeable seal from thin slurry. The
property of the cement slurry and its behavior depends on the components and the
additives in the cement slurry. Casing has been cemented in wells for more than 100
years. Cementing best practices have been known for more than 60 years. Best
practices have to be used by everyone to protect the environment and community and
to obtain maximum value from your.
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15. REFERENCES:
 Smith, D. K.: Cementing, SPE Monograph, 1987
 Davies, D. R., Hartog, J. J., Cobbett, J. S.: "Foamed Cement- A Cement
with Many Applications," SPE 9598, Middle East Oil Tech, Conf.
Manama, Bahrain, March 9-12, 1981.
 http://www.usoilandgas.net/cementing.htm
 http://gekengineering.com/Downloads/Free_Downloads/Cementing_
Chapter_3.pdf
 http://en.wikipedia.org/wiki/Cementation_(geology)
 http://www.rigzone.com/training/insight.asp?insight_id=317&c_id=1
 http://petrofed.winwinhosting.net/upload/30May-01June11/10.pdf
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