Well Design

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• Well Design
• PE 413
• Surface Equipments and Placement Techniques

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Surface Cementing Equiments
Jet Mixer
Dry cement must be mixed with the proper amount
of water to ensure that slurry and set-cement
properties are as designed. The jet mixer
induces a partial vacuum at the venturi throat,
drawing in the dry cement. High stream turbulence
then provides thorough mixing
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Surface Cementing Equiments
Jet Mixer
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Surface Cementing Equiments
Batch Mixer
Batch mixing and/or blending is achieved through
use of propellers, paddle mixers, pneumatic
mixing, and rotation of the cement tank
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Surface Cementing Equiments
Pump Skid Truck
The typical slurry-pumping unit is truck-mounted,
and contains diesel engines and displacement
tanks that are accurately graduated so that water
or mud volumes can be controlled to place the
slurry downhole properly.
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Surface Cementing Equiments
Cement Head

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Downhole Cementing Equipments
Basic Equipments
A predetermined volume of slurry is pumped into
the casing between two wiper plugs. The bottom
plug ruptures when it seats The top plug is
displaced with mud or completion fluid. Flow
stops and pressure builds when the top plug
lands. Check valves in the float shoe to prevent
backflow of the heavier column of slurry
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Downhole Cementing Equipments
Guide/Float Shoes and Collars
In most cases, except in certain shallow wells, a
round-nosed shoe is run on the bottom joint to
guide the casing past borehole irregularities
encountered while the string is run.
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Downhole Cementing Equipments
Guide/Float Shoes and Collars
Float equipment reduces derrick stress by
increased casing buoyancy. Float equipment
consists of casing shoes and collars which
contain check valves to prevent wellbore fluids
from entering. As the casing is lowered, the hook
load is reduced by the weight of fluid displaced.
The casing is filled from the surface to prevent
casing collapse.
Float collar
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Downhole Cementing Equipments
Wiper Plugs
Wiper plugs are used to separate cement from
preceding or following fluids. The bottom plug
removes mud from the wall of the casing, and
prevents this mud from accumulating beneath the
top plug.
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Downhole Cementing Equipments
Wiper Plugs

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Downhole Cementing Equipments
Casing Centralizers

• Casing centralizers are used to
• Improve displacement efficiency
• Prevent differential pressure sticking
• Keep casing out of key seats

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Downhole Cementing Equipments
Wipers and Scratchers

• Wipers and scratchers are used primarily to
  remove borehole mud cake. They also aid in
  breaking up gelled mud. Both rotating and
  reciprocating styles are available.

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Primary Cementing Techniques
Conductor
The conductor is usually the first and shortest
casing string. Its purpose is to protect shallow
sands from being contaminated by drilling fluids,
and help prevent wash-outs which can easily occur
near the surface because of loose, unconsolidated
formations. The depth is normally less than 300
ft. It can be used for the attachment of a
blowout preventer.
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Primary Cementing Techniques
Introduction
The objective of a primary cement job is to place
the cement slurry in the annulus behind the
casing. In most cases this can be done in a
single operation, by pumping cement down the
casing, through the casing shoe and up into the
annulus. However, in longer casing strings and in
particular where the formations are weak and may
not be able to support the hydrostatic pressure
generated by a very long colom of cement slurry,
the cement job may be carried out in two stages.
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Primary Cementing Techniques
Introduction
The first stage is completed in the manner
described above, with the exception that the
cement slurry does not fill the entire annulus,
but reaches only a pre-determined height above
the shoe. The second stage is carried out by
including a special tool in the casing string
which can be opened, allowing cement to be pumped
from the casing and into the annulus. This tool
is called a multi stage cementing tool and is
placed in the casing string at the point at which
the bottom of the second stage is required.
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Primary Cementing Techniques
Conductor

• Recommended cements for use with conductor casing
  are
• Accelerated neat
• Ready-mix concrete
• Thixotropic cement
• LCM additives
• When cementing down casing, plugs may not be
  used cement is simply placed
• The cement must have a compressive strength high
  enough to support the wellhead load therefore,
  high-compressive-strength cements are best.

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Primary Cementing Techniques
Surface Casing
Surface casing is usually the second string of
pipe set in the well. Shallow surface casing is
cemented in the same manner as conductor
casing. For deeper strings of surface casing, a
lightweight lead cement is used, followed by
heavier-weight completion cement to strengthen
the bottom of the surface casing around the shoe.
This creates a strong seal with the pipe and
formation for solid support of the casing.
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Primary Cementing Techniques
Surface Casing

• Recommended cement types include
• Accelerated cements
• LCM additives
• High-strength cements, which are often used
  on deep-well surface casing to support future
  strings
• The following is a brief summary of
  surface-casing cementing practices
• Both bottom and top plugs should be used to
  prevent mud contamination.
• Centralizers should be used.

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Primary Cementing Techniques
Intermediate Casing
The intermediate casing is the first string of
pipe set after the surface casing. Intermediate
casing strings extend from the surface to a
formation able to hold the mud weights expected
at greater depth. Unlike the conductor and
surface casings, additives such as friction
reducers, fluid-loss additives, and retarders are
required for intermediate slurries. Where the
annulus is small, friction reducers lower pump
pressures and reduce the chance of losing fluids
in a lost-circulation zone.
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Primary Cementing Techniques
Intermediate Casing

• The following is a brief summary of
  intermediate-casing cementing practices
• Both bottom and top plugs should be used to
  minimize contamination of the cement.
• Scratchers, centralizers, and flushes can be
  important in the successful completion of an
  intermediate-casing cementing job.
• This casing string can be cemented in a
  single-stage primary cement job, but a multistage
  job is often performed because such a tall
  annular column of cement slurry would exert a
  hydrostatic pressure greater than the formation
  pressure.

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Primary Cementing Techniques
Production Casing
The production casing is the last full string of
pipe set in the well, and extends to the
surface. The production casing is normally run
and cemented through a zone to be produced, and
then perforated to allow communication with the
formation. Sometimes it is set just above the
zone, and an openhohle completion is performed.
The production casing is normally the last casing
set in the well. It may be subjected to maximum
well pressures and temperatures, and must be
designed to withstand such conditions.
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Primary Cementing Techniques
Production Casing

• Recommended types of cement are
• Filler cements with high-strength tail-in
• Low-water-ratio cements (for all potential
  pay zones)
• Densified cements (for high competency and
  pressure control)
• Fluid-loss control additives

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Primary Cementing Techniques
Production Casing

• Recommended types of cement are
• Filler cements with high-strength tail-in
• Low-water-ratio cements (for all potential
  pay zones)
• Densified cements (for high competency and
  pressure control)
• Fluid-loss control additives

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Cementing Techniques
Single Stage Cementing Operation
The single stage primary cementing operation is
the most common type of cementing operation that
is conducted when drilling a well. In the case of
the single stage operation, the casing with all
of the required cementing accessories such as the
float collar, centralisers etc. is run in the
hole until the shoe is just a few feet off the
bottom of the hole and the casing head is
connected to the top of the casing. It is
essential that the cement plugs are correctly
placed in the cement head. The casing is then
circulated clean before the cementing operation
begins
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Cementing Techniques
Single Stage Cementing Operation
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Cementing Techniques
Single Stage Cementing Operation

1. The first cement plug (wiper plug) is pumped down
   ahead of the cement to wipe the inside of the
   casing clean.
2. The spacer is then pumped into the casing. The
   spacer is followed by the cement slurry.
3. This is followed by the second plug (shutoff
   plug). When the wiper plug reaches the float
   collar its rubber diaphragm is ruptured, allowing
   the cement slurry to flow through the plug,
   around the shoe, and up into the annulus. At this
   stage the spacer is providing a barrier to mixing
   of the cement and mud.
4. When the solid, shut-off plug reaches the float
   collar it lands on the wiper plug and stops the
   displacement process..

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Cementing Techniques
Multi-Stage Cementing Operation
When a long intermediate string of casing is to
be cemented it is sometimes necessary to split
the cement sheath in the annulus into two, with
one sheath extending from the casing shoe to some
point above potentially troublesome formations at
the bottom of the hole, and the second sheath
covering shallower troublesome formations. The
placement of these cement sheaths is known as a
multi-stage cementing operation
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Cementing Techniques
Multi-Stage Cementing Operation

• The reasons for using a multi-stage operation are
  to reduce
• Long pumping times
• High pump pressures
• Excessive hydrostatic pressure on weak
  formations due to the relatively high density of
  cement slurries.
• Cost due to the long distance between pay
  zones (reduce the high quality volume of cement
  required for the production zones)

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Cementing Techniques
Multi-Stage Cementing Operation
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Cementing Techniques
Multi-Stage Cementing Operation
First stage The procedure for the first stage of
the operation is similar to the single stage
operation, except that a wiper plug is not used
and only a liquid spacer is pumped ahead of the
cement slurry. The conventional shut-off plug is
replaced by a plug with flexible blades. This
type of shut-off plug is used because it has to
pass through the stage cementing collar which
will be discussed below.
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Cementing Techniques
Multi-Stage Cementing Operation
Second stage The second stage of the operation
involves the use of a special tool known as a
stage collar, which is made up into the casing
string at a pre-determined position. The ports in
the stage collar are initially sealed off by the
inner sleeve. This sleeve is held in place by
retaining pins. After the first stage is complete
a special freefall plug is released form surface
which lands in the inner sleeve of the stage
collar. When a pressure of 1000 - 1500 psi is
applied to the casing above the freefall plug,
the retaining pins on the inner sleeve are
sheared and the sleeve moves down, uncovering the
ports in the outer mandrel. Circulation is
established through the stage collar before the
second stage slurry is pumped.
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Cementing Techniques
Multi-Stage Cementing Operation
Stage collar installed in the casing for
multi-stage cementing operation
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Cementing Techniques
Liner Cementing
Liners are run on drillpipe and therefore the
conventional cementing techniques cannot be used
for cementing a liner. Special equipment must be
used for cementing these liners. As with a full
string of casing the liner has a float collar and
shoe installed. In addition there is a landing
collar, positioned about two joints above the
float collar. A wiper plug is held on the end of
the tailpipe of the running string by shear
pins. The liner is run on drillpipe and the
hanger is set at the correct point inside the
previous casing string. Before the cementing
operation begins the liner setting tool is backed
off to ensure that it can be recovered at the end
of the cement job.
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Cementing Techniques
Liner Cementing
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Cementing Techniques
Liner Cementing

• The cementing procedure is as follows
• Pump spacer ahead of cement slurry
• Pump slurry
• Release pump down plug
• Displace cement down the running string and out
  of the liner into the annulus
• Continue pumping until the pump down plug lands
  on the wiper plug.

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Cementing Techniques
Liner Cementing

1. Apply pressure to the pump down plug and shear
   out the pins on the wiper plug. This releases the
   wiper plug
2. Both plugs move down the liner until they latch
   onto landing collar
3. Pump the plugs with 1000 psi pressure
4. Bleed off pressure and check for back flow

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Liner Cementing
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Cementing Techniques
Squeeze Cementing

• Squeeze cementing is the process by which
  hydraulic pressure is used to force cement slurry
  through holes in the casing and into the annulus
  and/or the formation. Squeeze cement jobs are
  often used to carry out remedial operations
  during a workover on the well. The main
  applications of squeeze cementing are
• To seal off gas or water producing zones, and
  thus maximise oil production from the completion
  interval
• To repair casing failures by squeezing cement
  through leaking joints or corrosion hole

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Cementing Techniques
Squeeze Cementing

• To seal off lost circulation zones
• To carry out remedial work on a poor primary
  cement job (to fill up the annulus)
• To prevent vertical reservoir fluid migration
  into producing zones
• To prevent fluids escaping from abandoned
  zones.

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Cementing Techniques
Squeeze Cementing
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Evaluation of Cement Jobs

• A primary cement job can be considered a failure
  if the cement does not isolate undesirable zones.
  This will occur if
• The cement does not fill the annulus to the
  required height between the casing and the
  borehole.
• The cement does not provide a good seal
  between the casing and borehole and fluids leak
  through the cement sheath to surface.
• The cement does not provide a good seal at
  the casing shoe and a poor leak off test is
  achieved

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Evaluation of Cement Jobs

• A primary cement job can be considered a failure
  if the cement does not isolate undesirable zones.
  This will occur if
• The cement does not fill the annulus to the
  required height between the casing and the
  borehole.
• The cement does not provide a good seal
  between the casing and borehole and fluids leak
  through the cement sheath to surface.
• The cement does not provide a good seal at
  the casing shoe and a poor leak off test is
  achieved
• When any such failures occur some remedial work
  must be carried out. A number of methods can be
  used to assess the effectiveness of the cement
  job. These include

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Evaluation of Cement Jobs
Temperature Survey
(a) Temperature surveys This involves running a
thermometer inside the casing just after the
cement job. The thermometer responds to the heat
generated by the cement hydration, and so can be
used to detect the top of the cement column in
the annulus.
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Evaluation of Cement Jobs
Radioactive Surveys
(b) Radioactive surveys Radioactive tracers can
be added to the cement slurry before it is pumped
(Carnolite is commonly used). A logging tool is
then run when the cement job is complete. This
tool detects the top of the cement in the
annulus, by identifying where the radioactivity
decreases to the background natural radioactivity
of the formation.
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Evaluation of Cement Jobs
Cement Bond Logs
(a) Cement bond logs (CBL) The cement bond
logging tools have become the standard method of
evaluating cement jobs since they not only detect
the top of cement, but also indicate how good the
cement bond is. The CBL tool is basically a
sonic tool which is run on wireline. The distance
between transmitter and receiver is about 3
ft. Since the speed of sound is greater in casing
than in the formation or mud the first signals
which are received at the receiver are those
which travelled through the casing. If the
amplitude (E1) is large (strong signal) this
indicates that the pipe is free (poor bond).
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Evaluation of Cement Jobs
Cement Bond Logs