Well Design
Well Design - PE 413
Surface Equipments and Placement Techniques
Prepared by: Dr. Tan Nguyen
Well Design
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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Well Design
Surface Cementing Equiments
Jet Mixer
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Well Design
Surface Cementing Equiments
Batch Mixer
This is an old batch mixer.
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Well Design
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
Prepared by: Dr. Tan Nguyen
Well Design
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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Well Design
Surface Cementing Equiments
Cement Head
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Well Design
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
Prepared by: Dr. Tan Nguyen
Well Design
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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Well Design
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.
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Float collar
Well Design
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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Well Design
Downhole Cementing Equipments
Wiper Plugs
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Well Design
Downhole Cementing Equipments
Casing Centralizers
Casing centralizers are used to:
1. Improve displacement efficiency
2. Prevent differential pressure sticking
3. Keep casing out of key seats
Prepared by: Dr. Tan Nguyen
Well Design
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.
Prepared by: Dr. Tan Nguyen
Well Design
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 column of cement slurry, the cement job may be
carried out in two stages.
Prepared by: Dr. Tan Nguyen
Well Design
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.
Prepared by: Dr. Tan Nguyen
Well Design
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.
Prepared by: Dr. Tan Nguyen
Well Design
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 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.
Prepared by: Dr. Tan Nguyen
Well Design
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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Well Design
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.
Prepared by: Dr. Tan Nguyen
Well Design
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.
Prepared by: Dr. Tan Nguyen
Well Design
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 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
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. .
Prepared by: Dr. Tan Nguyen
Well Design
Primary Cementing Techniques
Production Casing
The following are some characteristics of production casing and its
application:
·
Common casing sizes are 4 1/2 in., 5 1/2 in., and 7 in.
·
Drilling mud is usually in good condition.
·
The cement job is usually not circulated, but cemented back to
intermediate casing depth.
·
A good cement job is vital to a successful completion.
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Well Design
Primary Cementing Techniques
Production Casing
To achieve a pressure-tight seal and protect the reservoir, special
consideration must be given to the production-casing cement properties.
As with intermediate casing and long surface pipe, both filler and
completion cement are usually employed.
The filler cement:
• Needs good fluid-loss control.
• Must have enough compressive strength to protect upper,
potentially productive zones which might be completed in the future.
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Well Design
Primary Cementing Techniques
Production Casing
The completion slurry needs to have good fluid control and sufficient
compressive strength to hold the weight of the pipe and to bond the
formation to the pipe.
The setting times of both slurries should be minimized to help prevent
cement contamination from formation fluids and formation contamination
by cement filtrate.
Prepared by: Dr. Tan Nguyen
Well Design
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
Prepared by: Dr. Tan Nguyen
Well Design
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
Prepared by: Dr. Tan Nguyen
Well Design
Cementing Techniques
Single Stage Cementing Operation
Prepared by: Dr. Tan Nguyen
Well Design
Cementing Techniques
Single Stage Cementing Operation
1. The first cement plug (wiper plug) is droped 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..
Prepared by: Dr. Tan Nguyen
Well Design
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
Prepared by: Dr. Tan Nguyen
Well Design
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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Well Design
Cementing Techniques
Multi-Stage Cementing Operation
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Well Design
Cementing Techniques
Multi-Stage Cementing Operation
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Well Design
Cementing Techniques
Multi-Stage Cementing Operation
Prepared by: Dr. Tan Nguyen
Well Design
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.
Prepared by: Dr. Tan Nguyen
Well Design
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.
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Well Design
Cementing Techniques
Multi-Stage Cementing Operation
Second stage
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.
Prepared by: Dr. Tan Nguyen
Well Design
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.
Prepared by: Dr. Tan Nguyen
Well Design
Cementing Techniques
Liner Cementing
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.
Prepared by: Dr. Tan Nguyen
Well Design
Cementing Techniques
Liner Cementing
The liner is run on drillpipe and the hanger
is set at the correct point inside the
previous
cementing
casing
string.
operation
Before
begins
the
the
liner
setting tool is backed off to ensure that it
can be recovered at the end of the cement
job.
Prepared by: Dr. Tan Nguyen
Well Design
Cementing Techniques
Liner Cementing
The cementing procedure is as follows:
1. Pump spacer ahead of cement slurry
2. Pump cement slurry
3. Release pump down plug
4. Displace cement down the running string
and out of the liner into the annulus
5. Continue pumping until the pump down
plug lands on the wiper plug.
Prepared by: Dr. Tan Nguyen
Well Design
Cementing Techniques
Liner Cementing
6. Apply pressure to the pump down plug and shear out the pins on the
wiper plug. This releases the wiper plug
7. Both plugs move down the liner until they latch onto landing collar
8. Pump the plugs with 1000 psi pressure
9. Bleed off pressure and check for back flow
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Well Design
Liner Cementing
Prepared by: Dr. Tan Nguyen
Well Design
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
Prepared by: Dr. Tan Nguyen
Well Design
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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Well Design
Cementing Techniques
Squeeze Cementing
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Well Design
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:
Prepared by: Dr. Tan Nguyen
Well Design
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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Well Design
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
radioactivity
identifying
where
the
decreases
to
the
background natural radioactivity of the
formation.
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Well Design
Evaluation of Cement Jobs
Cement Bond Logs
(c) 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).
Prepared by: Dr. Tan Nguyen
Well Design
Evaluation of Cement Jobs
Cement Bond Logs
Prepared by: Dr. Tan Nguyen
Well Design
Evaluation of Cement Jobs
Cement Bond Logs
Prepared by: Dr. Tan Nguyen