51 Cementjob

Cementing
CHECK values in EXERCISEs

Doruk Alp, PhD
© 2019 Doruk Alp, PhD 1

Casing Placement

Fracture
w/
Safety
margin
Kick

Cement job overview

How to fill annular space between
casing and formation, with cement?
• Remove the DS, lower the CS
• There are devices/apparatus within CS to:
• Separate fluids
• Prevent backflow of fluids
• Scrape casing surface
• Flush down spacer fluid followed by cement
• Flush down cement followed by spacer fluid, followed
by mud*
• Cement is :
• Either directly pumped into casing
• Or delivered beneath a certain depth using a DS
• with special BHA
• with typical BHA
• Using DS & BHAs is not preferred lest plugging of DS and BHA

Spacer fluid
Interim fluid to separate mud
and cement
IF NADF used as mud, the

spacer fluid should make the
casing and formation water-
wet.

The cement used in well
operations

2 types of Cement
• Non-Hydraulic Cement: the lime cycle cement

• Non-hydrating: does not absorb water
• Instead, takes in CO2 to harden.
• Not used for well operations.
• The original type of cement used since ancient times.
• Hydraulic Cement: the Portland cement
• Absorbs water (hydrates) to set & harden
• Used for several well operations; e.g. casing placement.
• Almost all contemporary cement are hydraulic cement;
i.e. also used in construction.

The Portland Cement:
“Hydraulic” cement sets by hydration
• CaCO3 + heat > calcination > CaO (lime) + CO2
• CaO (lime) + Silica (clay) + Alumina + slag* > @2000-2600 oF in a rotary kiln > clinker
• *stony waste matter separated from metals during the smelting or refining of ore.
• The resulting material, clinker, is cooled and inters-ground with small percentages of
gypsum to form Portland cement.
• Sand (SiO2), bauxite (Al), and iron oxide (Fe2O3) may be added to adjust composition of
the clinker for different types of Portland cement.
• The principal components of finished Portland cement are lime, silica, alumina, and iron.
https://www.researchgate.net/profile/Mert_Gurturk/publication/270395452/figure/fig3/AS:294198051520519@1447153689770/Fig-3-Schematic-diagram-of-counter-current-fl-ow-
rotary-kiln-con-fi-guration-21.png

The Portland Cement:
https://www.researchgate.net/profile/Mert_Gurturk/publication/270395452/figure/fig3/AS:294198051520519@1447153689770/Fig-3-Schematic-diagram-of-counter-current-fl-ow-
rotary-kiln-con-fi-guration-21.png

Kiln: Furnace where raw materials, i.e.
lime, slica and alumina react
http://www.ashokaengineering.com/wp-content/uploads/2015/05/kiln-shells-manufacturerers.jpg

Compound Formula Shorthand
Calcium oxide (lime) CaO C
Silicon dioxide (silica) SiO2 S
Aluminum oxide (alumina) Al2O3 A
Iron oxide Fe2O3 F

Ingredients react in the kiln to produce clinker
Water H2O H
Sulfate SO3 S
Compound Formula Shorthand %wt

Tricalcium aluminate 3CaO·Al2O3 C3 A 10
Tetracalcium aluminoferrite 4CaO·Al2O3·Fe2O3 C4AF 8
Belite or dicalcium silicate 2CaO·SiO2 C2 S 20
Alite or tricalcium silicate 3CaO·SiO2 C3 S 55
Sodium oxide Na2O N
0-2
Potassium oxide K2O K
Gypsum CaSO4.2H2O CSH2 5
http://www.engr.psu.edu/ce/courses/ce584/concrete/library/construction/curing/Composition%20of%20cement.htm
The end product: Clinker
Ground clinker is packed as sacks of cement
http://www.cementkilns.co.uk/images/clinker_thumb.jpg

The setting of “cement”
Hardening/Thickening/Freezing/Drying of Cement.
“Drying” of cement: Portland cement actually absorbs water;
i.e. hydrated, to become solid/hard concrete.

Portland cement sets not by actually
“drying” but by hydrating:
• When water is added to cement, setting and
hardening reactions begin immediately.
• The chemical compounds in the cement undergo
hydration and re-crystallization, resulting in a “set”
product.
• When cement is “setting up” the material is
transforming from liquid into a jelly like semi-solid
state.
• Similar to gelation of mud, except this process is
permanent.
• This phase is called the thickening of cement.
Portland cement “dries”; i.e. sets/hardens, not by actually
drying (H2O evaporating) but by hydrating (absorbing H2O).
IADC Drillers Knowledge Book, 2015

Hydrostatic loss due to setting of
cement
• As cement thickens, it becomes difficult to pump
• This marks the beginning of cement becoming concrete.
• Same effect is observed as drilling fluid gels.
• Vertical stress (or pressure) applied at the top of a
column of such material is not transmitted throughout
the material undiminished; i.e.
• either not transmitted at all
• Or transmitted only partially (i.e. less)
• The drop in hydrostatic p. at hole bottom could cause
formation fluids enter into the wellbore.
• Should we apply additional pressure at the top of the
annulus to make-up for the pressure loss as cement
hardens?
Hydrostatic loss due to setting of
cement

Poor cement job: Wormholes
• Liquid phase pressure of cement slurry may

decrease below the pore p. as cement sets.
• If the formation fluid is gaseous, it easily flows into
the wellbore and rises within the cement sheath as
cement sets.
• This creates continuous paths called “wormholes”
within the concrete and allow formation fluids to
flow within the cement sheath in the annulus.
• poor cement job!
• Cement bond log to QC completed job

Gel Strength vs Yield point
Cement slurry is best described by Bingham-plastic model
“Gelled” fluid:
Fluid remained at rest
for adequately long duration.
© 2019 Doruk Alp, PhD Steve Devereux 1998 22

CSGS: the critical static gel strength of
the cement
• Pressure transmission through a column of cement begins to decay with
setting/hardening.
• As the cement hardens it provides increased resistance against lighter
fluids trying to penetrate through upwards: “gel strength”
• Similar to gel strength observed in mud
• How static gel strength for the cement changes with p. is determined
empirically in the lab.
• CSGS: the critical static gel strength is the gel strength required to keep
formation fluid (gas) from rising up in the cement when hydrostatic p. of
the cement column equals pore p. across a potential flow formation.
• Required CSGS, and thus the type of cement for the job, is determined
based on anticipated pore p., formation fluid type & density:
• As the cement hardens, hydrostatic p. drops.
• When hydrostatic p = pore p., formation gas enters the wellbore.
• What is the required SGS to keep gas penetrating through the cement at this
point? (CSGS)

CSGS: the critical static gel strength of
the cement
•
•
• Where,
• OBP: overbalance pressure

Assume casing shoe at 1000 ft.
Ppore @ 1000 ft = 0.433 * 1000 = 433 psi
Pbh due to cement = 0.052 * 18 * 1000 = 936 psi
OBP = 936 – 433 = 503 psi
OBP SGS at 433 psi = 225 psi < 500 psi (CSGS),
there is risk of wormholes

Slurry properties for
cement job design
Slurry is the liquid mixture of cement+water+others

Slurry Design
• A well plan is not complete until the (cement)

slurry has been designed.
• Major aspects of the design are as follows:
• Density selection
• Cement type and amount
• Mixing water & other additives
• Volumetric requirements
• Pump strokes

Parameters for the design of slurry:
• Downhole temperature > cement class

• Pore & Fracture p. > slurry density
• Pore p. & fluid density (nature) > compressive
strength
• Downhole depth > thickening time
• Fluid loss > Mix. water
• Volume behind casing > Yield

Slurry Density
• The slurry density must be sufficient to prevent

kick and blowouts. Yet it should not cause lost
circulation.
• Slurry density or “weight” usually expressed in ppg
• Calculation is based on the following equation:
• Slurry weight = (lb cement + lb water + lb addit.) /
(gal cement + gal water + gal addit.)

Bulk vs Absolute Density
• Cement has a bulk density of 94 lb/ft3 (& 1 ft3/sk)

• An absolute density of 94/0.48 = 195.8 lb/ft3
• 0.48 ft3 is actual volume of cement (clinker) in 1 ft3
• Thus: SG_cement = 195.8/62.4 = 3.14.
• The absolute volume of all solid constituents must
be calculated in gallons, where:
• Abs. Vol. [gal] = (lb of material) / (8.34 ppg x
SG_material)

The yield of the cement
• The yield of the cement [ft3/sack], is the volume that
will be occupied, by set slurry (i.e. hardened mix of
cement, water and additives), when slurry is mixed
according to design specifications.
• The volume of slurry to be realized from 1 sack of cement
when mixed with a specified amount of water and possibly
other additives is called the yield (ignoring any volume
change after setting).
• The yield in cubic feet per sack of cement is :
• Yield = (gal cement + gal water + gal additive) / 7.48 [gal/ft3]
• A major factor affecting the slurry yield is the density.
• Water must be added in significant volumes to achieve low
weight cements that will not fracture shallow or weak zones.

Water requirements
• The mixing water requirements vary, depending

primarily on cement class and slurry density.
• Quality of mixing water is an important parameter
in cement planning. The hydration and curing of
the slurry will react differently with varying
amounts of salt, calcium, or magnesium the mix
water.
• Most cement jobs use well site water.

Azar 2007

The compressive strength
• A 500psi minimum compressive strength is

recommended before drilling operations resume,
but higher strengths are preferred.
• Temperature affects the compressive strength of
the cement.
• Higher temperatures reduce the time for the
cement slurry to reach some compressive levels.
• However, at temperatures above 230 oC, cement
strength begins to decrease.

Thickening Time

Thickening time
• Is the duration when cement remains pumpable

with reasonable pressures. Perhaps the most
critical property in the displacement process.
• Factors affecting the thickening time include
cement composition and temperature.

Fluid loss
• The water lost from the slurry to the formation

during slurry placement operations.
• If large volume of water is lost, the slurry becomes
too viscous or dense to pump.
• Neat cement (cement with no special additives)
has a fluid loss rate in excess of 1000 cc/30 min.
0-200 cc/30 min Good control
200-500 cc/30 min Moderate control
500-1000 cc/30 min Fair control
Over 1000 cc/30 min No control
Cement Additives
• Neat slurry is a mixture of water and cement only.

• Special chemicals are often added to the slurry to
achieve some desired purpose. These additives are:
• Accelerators,
• Retarders,
• Density Adjuster,
• Dispersants,
• Fluid Loss Additives

Accelerators
• Most operators wait for cement to reach a minimum of
500 psi compressive strength before resuming
operations.
• At temperatures below 100 oF common cement may
require a day or two to develop 500 psi strengths.
• Accelerators are useful at reducing the amount of
waiting-on-cement (WOC) time.
• Low concentration of cement accelerators, usually 2-4
% by weight of cement, shorten the setting time of
cement and promote rapid strength development.
• Calcium chloride is perhaps the most commonly used
chemical for this purpose.

Retarders
• High formation temperatures associated with

increased well depths necessitate the use of
chemicals that retard the setting time of the
cement; i.e. increase the pumping time.
• The most common retarder may be calcium
lignosulfonate. Its effectiveness is limited in
temperatures above 200 oF.
• Other retarders such as carboxy-methyl-hydroxy-
ethylcellulose, can be used to about 240 oF.

Density Adjusters & Dispersants
• High formation pressures for neat slurry densities
require additions in cement density. Formations with
low fracture gradients require reductions in cement
weight.
• Dispersants as an additive can increase slurry densities
to 17.5 ppg due to their effect on viscosity. Adding
more water to the slurry and adding materials to
prevent solid separation achieve density reductions.
• Dispersants provide several beneficial features for the
slurry.
• Reduce slurry viscosity
• Allow slurry turbulence at lower pump rates
• Assist in providing fluid loss control for densified slurries

Fluid Loss Additives
• Fluid loss agents are used in cement slurries for the

following reasons:
• Minimize cement dehydration in the annulus
• Reduce gas migration
• Improve bonding
• Minimize formation damage.

API Cement Classes
The API has established a classification system for cements
used in oil and gas operations.
Major criteria is depth & temperature range.

API Classification
and Applications of API Cements
Class-A
• Used at a depth range of 0 – 6000 ft.
• Used at a temperature of up to 170 oF.
• Intended for use when special properties are not
required; well conditions permit.
• Economical compared with premium cements.
Class-B
• Used at a temperature of up to 170 F.
• Intended for use when moderate to high sulfate
resistance is required; well conditions permit.
• Economical compared with premium cements.

Class-C
• Used at a temperature of up to 170 oF.
• Intended for use when early strength is required;
its special properties are required.
• High in tricalcium silicate.

Class D & E
• Class-D is used at a depth range of 6000 – 10000 ft.
• Class-E is used at a depth range of 10000 – 14000 ft.
• Class-D is used at a temperature of 170 oF to 260 oF.
• Class-E is used at a temperature of 170 oF to 290 oF.
• Intended for use when moderately high temperature and
high pressure are encountered; its special properties are not
required.
• Available in types that exhibit regular and high resistance to
sulfate.
• Retarded with an organic compound, chemical composition
and grind.
• More expensive than Portland cement.

Class F
• Used at a temperature of 230 oF to 320 oF.
• Intended for use when extremely high temperature
and high pressure are encountered; its special
properties are not required.
• Available in types that exhibit moderate and high
resistance to sulfate.
• Retarded with an organic compound, chemical
composition and grind.
Class G & H
• Used at a temperature up to 200 oF without modifiers. A
basic cement compatible with accelerators or retarders.
• Useable over the complete range of classes A to E with
additives.
Class J
• Used at a temperature of 170 oF to 320 oF without
modifiers.
• Useable with accelerators and retarders.
• Will not set at temperature less than 150 oF if used as a
neat slurry.

Slurry Design

Compare to mud calculations
• Always ideal mixing, unless stated otherwise

• wt% gel implies
• Percent Mix implies wt% water; i.e. ratio of water
mass to cement mass
•

Example 1
• Calculate the weight, percent mix and yield (set

volume) of the slurry with given properties:
WCR: water-cement ratio = 5.5 gal/sx
SG_cement = 3.14
1 sx of cement = 1 cu ft = 94 lb
(1 cu ft includes air volume, i.e. it is the bulk volume)
Density of water = 8.34 ppg

•
𝑙𝑏 𝑔𝑎𝑙 𝑙𝑏
𝑠𝑥 𝑠𝑥 𝑔𝑎𝑙
• 𝑙𝑏
94𝑠𝑥 𝑔𝑎𝑙
𝑙𝑏 𝑠𝑥
8.33 ∗3.14
𝑔𝑎𝑙
• 𝑔𝑎𝑙
𝑐𝑢𝑓𝑡
𝑙𝑏 𝑙𝑏 𝑔𝑎𝑙
𝑠𝑥 𝑔𝑎𝑙 𝑠𝑥
• 𝑔𝑎𝑙
𝑐𝑢 𝑓𝑡.

• Absolute Volume, gal = (lb of material) / (8.34 lb/gal
x spec. grav. of material)
• Absolute Volume = 94 lb/sx / (8.34 lb/gal x 3.14)
• Absolute Volume = 3.6 gal/sx
• Percent Mix = (5.5 gal/sx x 8.34 lb/gal x 100) / 94
lb/sx
• Percent Mix = 48.8 % water by weight of cement

Example 2
• Calculate the number of sacks of class A cement

and bentonite required to obtain cement returns
on surface casing.
Hole Size = 12.5 inches
Casing to be landed at 1400 ft
Volume of 9 5/8 inch 40 lb/ft casing = 0.4256 ft3/ft
EMW at 1400 ft = 14.10 lb/gal (= Slurry weight)
Excess cement required = 35 %
Bumper plug at 30 ft (thickness of cement plug at the
tip of casing, h = 30 ft )
Example 2: Soln
Find % gel (Bentonite) to match required EMW:
For Class-A cement read/interpolate from Table 3.10 for rho = 14.1 ppg:
4%wt gel is required, water-cement ratio increases to 7.8 gal/sx and yield
for 1 sack of cement is ~ 1.55 cu ft/sack
(OR calculate using data from Table 3.9 or Table 3.6, see following pages)
Find total volume:

Cement left in casing = 30 ft x 0.4256 ft3/ft = 12.77 ft3
Cement to fill annulus = 1400 ft x 0.3469 ft3/ft x (1+0.35[excess])
Cement to fill annulus = 655.64 ft3
Total Cement required = 12.77 + 655.64 = 668.41 ft3

Find total sacks and gals of each component:
Sx of cement required = 668.41 cu ft/1.55 cu ft/sx =
432 sx
lbs of cement = 432 sx * 94 lb/sx = 40608 lb
Bentonite required = 40608*4/100 = 1624 lb or
16.24 sx (1 sack of Be = 100 lb)
Water required = 432 * 7.8 = 3370 gal.

Calc wt% Be to obtain desired cement weight using
wt% water requirements
One can solve above eqn. or prepare tables/plots as shown next.

wt% Be Wc Wwc WBe WwBe Ws Vc VBe Vw Vs gamma
- lb lb lb lb lb gal gal gal gal ppg
0% 94.00 43.24 0.00 0.00 137.24 3.59 0.00 5.19 8.78 15.62
1% 94.00 43.24 0.94 4.98 143.16 3.59 0.04 5.79 9.43 15.19
2% 94.00 43.24 1.88 9.96 149.08 3.59 0.09 6.39 10.07 14.81
3% 94.00 43.24 2.82 14.95 155.01 3.59 0.13 6.99 10.71 14.47
4% 94.00 43.24 3.76 19.93 160.93 3.59 0.17 7.58 11.35 14.18
5% 94.00 43.24 4.70 24.91 166.85 3.59 0.22 8.18 11.99 13.91
6% 94.00 43.24 5.64 29.89 172.77 3.59 0.26 8.78 12.63 13.68
7% 94.00 43.24 6.58 34.87 178.69 3.59 0.30 9.38 13.28 13.46
8% 94.00 43.24 7.52 39.86 184.62 3.59 0.35 9.98 13.92 13.27
9% 94.00 43.24 8.46 44.84 190.54 3.59 0.39 10.57 14.56 13.09
10% 94.00 43.24 9.40 49.82 196.46 3.59 0.43 11.17 15.20 12.93
11% 94.00 43.24 10.34 54.80 202.38 3.59 0.48 11.77 15.84 12.78
12% 94.00 43.24 11.28 59.78 208.30 3.59 0.52 12.37 16.48 12.64
13% 94.00 43.24 12.22 64.77 214.23 3.59 0.56 12.97 17.12 12.51
14% 94.00 43.24 13.16 69.75 220.15 3.59 0.61 13.56 17.77 12.39

16.00
15.50
15.00
14.50
14.00
gamma ppg
13.50
13.00
12.50
12.00
11.50
11.00
0% 2% 4% 6% 8% 10% 12% 14% 16%
wt% Be

Cement Job Tools

• Planning for cement job involves evaluating and
selecting equipment to be used with the cementing
process.
• The down-hole equipment includes:
• shoes and collars that are run as integral sections of the
casing string.
• centralizers, scratchers and cement baskets.

Casing shoe
• Casing Shoe: A casing shoe is a short, heavy walled

pipe run on the bottom of the casing string. It has a
rounded “nose” to guide the casing into the hole.
The shoe is screwed on the casing and generally is
“glued” with a thread-locking compound.
• Casing shoes are generally available in three types:
• guide shoe
• float shoe and
• differential fill shoe.
• A guide shoe contains an orifice through the center
that allows mud to pass freely.
Casing shoe
• A float shoe contains a back pressure valve called a float
valve.
• This valve prevents mud from flowing into the casing from
the bottom yet allows fluid to be pumped through the shoe.
• Thus, cement being heavier, is prevented from U-tubing
back into the casing
• Also, impact of changes in surface casing pressure on (or
vacuum due to) cement u-tubing is prevented.
• The driller must fill, or partially fill, the casing with mud
periodically to prevent casing collapse as the annulus
hydrostatic pressure increases with depth.
• Differential fill shoe are similar in concept to float shoes.
Collars
• Collars: A cementing collar is typically run as an
integral part of the string and is placed at the top of
the first or second casing joint.
• The collar serves as a stop for the cement wiper
plug so that all the cement is not inadvertently
pumped completely out of the casing and into the
annulus.
• Multi-stage cementing requires special collars with
sliding sleeves and ports. The sleeves are usually
closed during the primary stage of cementing. The
sleeves are activated with either the free-fall or
displacement methods.

Figure 4-1 Guide shoe (Courtesy World Oil’s Cementing Book)
Figure 4-2 Float Collar (Courtesy World Oil’s Cementing Handbook)

Centralizers
• Placed on the exterior of the casing string to
provide stand-off distance between the well bore
and the casing to attain cement encirclement of the
pipe.
• Centralizers (Courtesy World Oil’s Cementing Handbook)

Scratchers, Baskets
• Scratchers: To achieve an effective cement job, the

slurry must bond to the formation.
• Scratchers assist by scraping and scratching the
mud cake on the formation to promote bonding to
the virgin formation.
• Cement Baskets: Cement baskets provide support
for the column of cement while it cures, or
hardens.
• The baskets are often placed above lost circulation
zones that cannot support a full column of cement.

Plugs
• Cement slurry is normally separated from the mud

column by plugs that minimize interface
contamination.
• The bottom plug has a diaphragm that is ruptured
with pump pressure after it seats on the collar or
shoe.
• The top plug has a solid aluminum insert. The plugs
are mounted in a cementing head at the top of the
casing.

Cement plugs
Cementing plugs: (a) top and (b) bottom plugs

(Courtesy of Schlumberger)

Cement Job Design

Types of Cement Jobs

Cementing
• 3 types: • Primary cementing: placed

• Primary cementing behind the casing in a:
• Squeeze cementing • single stage OR
• Plug cementing • multi-stage technique.
• Primary Cementing to • Single Stage Cementing:

isolate zones: • pump cement down the
• Protect weaker shallow casing and up to annulus.
zones behind the casing • The cement, being heavier, is
from high-p formations prevented from U-tubing by
below the casing. back-pressure valves (float
• Separate producing zones shoe/collar) in the bottom of
from water bearing the casing string.
formations.

Main reasons for staged cementing
• Isolating potential flow zones during well construction
• Thickening time.
• Particularly the lead/head section of the slurry may freeze before reaching
target location; i.e. high up in the annular area between casing and formation.
• Excess pressure.
• Slurry density can only be lowered down to certain levels (excess water
weakens the concrete)
• Heavy slurry creates excess pressure against the formation.
• This may fracture the formation and cause loss of slurry.
• Loss of hydraulic communication.
• As the cement sets, its weight is now loaded on the casing and formation.
• Thus, not enough pressure is exerted on the slurry remaining below
• Further, concrete does not allow transmission of any pressure.
• Therefore, BHP drops below pore p.
• Formation gas entering into wellbore would rise up in the thickening slurry,
creating wormholes.

Parameters controlling the max. height
of cement job
• Pore & Fracture p.
• Formation fluid type & density
• Slurry density
• Thickening time
• must be determined empirically
• Slurry gel strength
• must be determined empirically
• Adjust gel strength to prevent formation gas from rising
in the slurry.

Primary cementing:
Multi Stage Cementing
• Initial stage is usually planned as a single stage
effort.
• Following stages are pumped through special ports
opened in the casing at the desired location.
• Each port is opened after previous stage is
cemented.

Single stage 2 batch cementing:
Lead & tail sections.
• Under certain conditions:
• Slurry density is within limits of pore & fracture p. and
• Only issue is the thickening time
• Multi-stage cement job may be avoided by
delaying the thickening of lead section.
• Add retarders to the lead section
• Or, add accelerators to the tail section.
• See pertinent question in the following pages.

[min]

Primary Cementing Technique
• The single stage method is traditionally for

conductor, surface, intermediate and production
casing strings.
• Procedure:
1. Drill to desired depth.
2. Pull drill string and run intermediate casing.
3. Circulate hole with rig pump.
4. Attach cementing head with plugs to casing.
5. Connect lines to pump truck and cementing head.
6. Start circulation with pump track.
7. Release bottom plug.

Primary Cementing
8. Pump spacer to remove mud.

9. Mix cement and displace until all cement is mixed
and inside the casing.
10. Release plug.
• Release top plug for a single-step job.
• Release bottom shut-off plug for second-stage job
11. Pump until sharp pressure increase is noted on
pump truck gauge, indicating top plug has
bumped.

Primary Cementing
Step 12-16 is for staged cementing
12. Drop bomb, open ports.
13. Circulate any excess cement around the stage tool.
14. Wait at least 6 hr. for cement to gain initial
strength.
15. Mix second stage cement and displace until all
cement is mixed and in casing.
16. Release top closing plug and displace until a sharp
increase is noted on the pump truck gauge,
indicating the plug has bumped.
17. Release pressure to determine if single stage or stage
tool is holding.
Squeeze Cementing
• Supplement/repair a faulty primary cement job

• Reduce water-oil, water-gas and gas-oil ratio
• Repair casing leaks
• Stop lost circulation in an open hole while drilling
• Bring a well under control.

Liner and Squeeze Cementing
• The liner is run on the bottom of the drill pipe with

a hanger and setting tool.
• Hangers are usually set mechanically or with a
hydraulic action.
• Plugs sweep cement from the interior of the liner
to the float collar.
• If primary cement job is not successful, squeeze
cementing will not be required. However, potential
problems must be considered to overcome poor
primary jobs.

Liner and Squeeze Cementing
• Application for squeeze cementing in drilling and

producing operations include:
- casing shoe;
- liner top
- perforation
- plug a producing zone or sections of the zone
- seal lost circulation problems.

Cement Job Design
Other important aspects

Impact of mud-cake on cement job:
(Hao et.al. 2016)
• While drilling, mud-cake is indispensable for protecting formation from
the invasion of drilling fluid and associated damage.
• Yet, cement fails to bond effectively with the formation when there is
the mud-cake (Opedal et al., 2014).
• Several studies to show detrimental effect of mudcake on cement job:
Griffith and Osisanya, 1995; Bailey et al., 1998; Ladva et al., 2005;
Agbasimalo and Radonjic, 2014; Opedal et al., 2014; Plank et al., 2014
• And numerous authors studied mudcake removal prior to cementing:
Zain and Sharma, 1999; Rostami and Nasr-El-Din, 2010; Al-Arfaj and
Amanullah, 2014
• Spacer fluids or chemical washes cannot completely remove mudcake
from borehole walls (Guillot et al., 2007).
• Challenge: formulate a mud that forms a thin and impermeable
mudcake during drilling operations, yet:
• easily lifted-off, or
• can feasibly bond with the cement sheath and the formation adjacent the
mudcake.

Impact of mud gel strength
• Gelled mud surrounds the casing when it reaches
bottom.
• Difficult to remove/push gelled mud; particularly in the
narrow annulus
• Flow is diverted to the larger regions in the annulus as
cement passes through this interval.
• Cement displaces gelled drilling fluid more easily in the
large areas (near the smallest stress) than in the small
areas (near the largest stress)
• Without centralizers and pipe movement, very little
cement would move into the narrow region of the
annulus.
• Move the casing (preferably ”rotate”) while cement is
displacing the drilling fluid in the annulus.
Impact of mud gel strength

Remedy
• The drilling fluid should be modified so that it can

be more easily displaced by cement.
• This modification should be performed while the
drill bit is in the hole, just prior to running casing,
after cuttings cease arriving at the surface

Displacement

Displacement Process:
Pumping the cement into the annulus
• The displacement rate affects the flow regime in the
annulus. High flow rates convert the flow regime from
laminar to turbulent.
• Although annular turbulent flow is not desirable in
most drilling operations, it is desirable in cementing
operations because it erodes the mud cake on the
formation.
• Contamination of the interface between the mud and
cement is a problem that can reduce the effectiveness
of the cement job.
• This problem is addressed by separating the mud and
cement with a spacer fluid.
• IF used NADF as mud, the spacer fluid should make
the casing and formation water-wet.

Questions

Single cement
setting


Single stage, 2
batch, 2 separate
setting times

[min]


Example 5
• A 7 5/8 inch 39 lb/ft production casing string will be run

inside 51 lb/ft (ID=9.85 in), 10 ¾ surface casing set at
2000 ft.
• The bottom of the 9 inch hole is at 9100 ft (casing seat).
• A 6 ½ inch x 18 inch duplex pump will be used to pump
the cement plug against the float shoe. If the pump
operates at 90 % efficiency
• How many strokes will be required?
• After the job was completed, the drilling engineer at
the well site observed that 1990 strokes were required
to bump the plug. What is the actual pump efficiency?

Example 5:
Compute the volumes of casing and annulus.
• 7 5/8 inch pipe capacity = 0.3171 cu ft / lin ft; 0.0565 bbl /
lin ft
• 7 5/8 in. x 9 inch hole annulus = 0.1247 cu ft / lin ft
• 7 5/8 in. x 9.85 inch annulus = 0.2121 cu ft / lin ft ; xxx bbl /
lin ft
Compute pipe and annulus capacities:
• 7 5/8 inch pipe capacity = 910 ft x 0.0426 bbl / lin ft = 387.6
bbl
• 7 5/8 in. x 9 inch hole annulus = (9100 – 2000) ft x 0.0222
bbl/lin ft = 157.6 bbl
• 7 5/8 in. x 9.85 inch annulus = 2000 ft x 0.0382 bbl / lin ft =
76.4 bbl

Example 5:
pump factor
• The pump factor for a duplex pump can be
determined using Equation 1.10
•

Example 5:
Pump efficiency
• The output of the 6 ½ inch x 18 inch duplex pump is
obtained as:
0.2280 bbl/stroke = 100 % efficiency
0.2052 bbl/stroke = 90 % efficiency
• Determine the pump stroke requirements to bump the
plug.
387.6 bbl / (0.2052 bbl / stroke) = 1888 stroke
• If the pump required 1990 strokes, determine the
output.
387.6 bbl / 1990 strokes = 0.1948 bbl / stroke
• Determine the actual efficiency.
(0.1948 bbl/stroke) / (0.2280 bbl/stroke) x 100 = 85.4 %

Example 6
• A 3000 ft 13 3/8 inch surface casing is to be

cemented in a 17.5 inch hole.
• The 1000 ft tail slurry is 14.2 lb/gal Class-A cement
with 4 % gel.
• The remaining lead slurry is 12.2 lb/gal Class-A
cement with 16 % gel.
• Use 100 % volumetric wash out.
• Compute the cement, water and gel requirements.

Example 6:
The annulus volume is computed as:
• 0.6946 cu ft / lin ft x 2000 ft = 1389.2 cu ft
• 0.6946 cu ft / lin ft x 1000 ft = 694.6 cu ft
Accounting for 100 % wash outs:
• (2000 ft lead slurry) : 1389.2 x 2 = 2778.4 cu ft
• (1000 ft tail slurry) : 694.6 x 2 = 1389.2 cu ft

Example 6:
Lead slurry calculations are as follows:
• Cement: 2778.4 cu ft / (2.55 cu ft/sx) = 1089.5 sx of cement
• Gel: (1089.5 sx) (16 % gel) (94 lb/sx) = 16386 lb gel = 163.86 sx of gel
• Water: 14.7 gal/sx x 1089.5 sx = 16015 gal = 381 bbl
Tail slurry calculations are as follows:
• Cement: 1389.2 cu ft / (1.52 cu ft / sx) = 913.9 sx of cement
• Gel: (913.9 sx) (4 % gel) (94 lb/sx) = 3436 lb gel = 34.4 sx of gel
• Water : (913.9 sx) x 7.57 gal/sx = 6918 gal = 164.7 bbl

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Cementing

CHECK values in EXERCISEs

© 2019 Doruk Alp, PhD 1

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IF NADF used as mud, the

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• Non-Hydraulic Cement: the lime cycle cement

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Calcium oxide (lime) CaO C

Silicon dioxide (silica) SiO2 S

Aluminum oxide (alumina) Al2O3 A

Iron oxide Fe2O3 F

Compound Formula Shorthand %wt

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IADC Drillers Knowledge Book, 2015

IADC Drillers Knowledge Book, 2015

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• Liquid phase pressure of cement slurry may

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© 2019 Doruk Alp, PhD Steve Devereux 1998 22

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IADC Drillers Knowledge Book, 2015

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• A well plan is not complete until the (cement)

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• Downhole temperature > cement class

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• The slurry density must be sufficient to prevent

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• Cement has a bulk density of 94 lb/ft3 (& 1 ft3/sk)

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• The mixing water requirements vary, depending

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• A 500psi minimum compressive strength is

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• Is the duration when cement remains pumpable

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• The water lost from the slurry to the formation

• Neat slurry is a mixture of water and cement only.

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• High formation temperatures associated with

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• Fluid loss agents are used in cement slurries for the

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