Chapter5 New (Cementing)[1]

7/31/2019 Chapter5 New (Cementing)[1]

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Cementing

DRILLING ENGINEERING


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CEMENTING

The purposes of this chapter are to present:

1. The primary objectives of cementing

2. The test procedures used to determine if thecement slurry and set-cement have suitable

properties for meeting those objectives.

3. The common additives used to obtain the

desirable properties under various wellconditions.

4. The techniques used to place the cement at

the desired location in the well.


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3.1 Composition of Portland Cement

Portland cement made by burning limestone and clay.

Oxides of Ca, Al, Fe, Si react at high temperatures in theKlin (26002800 oF).

When it cools, it becomes balls of cement clinker.

After aging in the storage, the seasoned clinker is taken tothe grinding mills where gypsum is added to (CaSO4.2H2O)

to retard setting time and increase ultimate strength.

It is sold in units of barrels = 376 lbm or four, 94 lbm sacks.

TYPES OF CEMENT


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Cement is thought to be made up of four crystalline components

in the clinker that hydrate to form a rigid structure.

1. Tricalcium silicate (3 CaO.SiO2 or C3S)

2. Dicalcium silicate (2 CaO.SiO2 or C2S)

3. Tricalcium Aluminate (3 CaO.Al2O3 or C3A)4. Tetracalcium aluminoferrite(4CaO.Al2O3.Fe2O3C4AF)

The reaction is exothermic and generates a considerable quantity

of heat.

The main cementing compound is 3CaO.2SiO2.3H2O or

tobermorite gel = it has extremely fine particle size.


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Manufacturing of Portland Cement


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3.2 Cement Testing

API : Recommended Test procedures

Test Equipment

1. Mud balance:to determine slurry density.

2. Filter press:to determine filtration rate.

3. Rotational viscometer:to determine rheological properties.

4. Consistometer:to determine thickening rate characters.

5. Cement permeameter:to determine permeability ofthe set cement.

6. Specimen molds and strength testing machines for

determining the tensile and compressive strength.

7. Autoclave :to determine the soundness of cement.

8. Turbidimeter :to determine the fineness of cement.


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3.3 Standardization of Drilling Cements

API has defined eight standard classes and three standard

types of cement for use in wells.

Classes are designated by letters A to H. Types are designated by O, MSR, HSR

To provide uniformity in testing it is necessary to specify

the amount of water to be mixed with each type of cement.

Water content ratio, or normal water content or API

water of the cement class. Table 3.6


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Well depth and cementing time relationship used in

definition of API cement classes.


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10Physical Requirement of API Cement Types.


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For each wt% of bentonite added the water content should

be increased by 5.3%

For each wt% of barite added 0.2% of water should be

added.

For 3.5 : Cement mixing time = 20 cuft/min

Displacement rate = 50 cuft/min

Casing OD = 7.0 in,

Area of Casing = 33.57 sq.in.


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Protect and support the casing Prevent movement of the fluid through the annular

space outside the casing

Stop the movement of fluid into regular or fractured

formations. Close an abandoned portion of the well.

Cement slurry is made by mixing powdered cement and

water.

It is placed by pumping it to the desired location.

The hardened-reacted-cement slurry becomes set cement

a rigid solid that exhibits strength.

PROPERTIES OF CEMENT


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At present the cement classes G and H can be modified easily

through the use of additives to meet almost any job

specifications economically.

Types of cement additives:

(1)Density control additives(2)Setting time control additives

(3)Lost circulation additives

(4)Filtration control additives

(5)Viscosity control additives

(6)Special additives

Yield of cement: the volume of slurry obtained per sack of

cement used.

Percent mix: Content of water expressed as weight percent.

3.4 CEMENT ADDITIVE


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3.4.1 Density Control:

The density of the cement slurry must be high enough toprevent the higher pressured formation fluids from flowing

into the well during cement operation. Yet not so high as to

cause fracture of the weaker formations.

Cement density is reduced by using a high water cementratio, or adding low specific gravity solids, or both.


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Low specific gravity solids used to reduce slurry densityinclude:

1. Bentonite2. Diatomaceous earth3. Solid hydrocarbons4. Expanded perlite5. Pozzolan

Slurry density usually is increased by using a lower watercontent or adding high specific gravity solids. High specificgravity solids used to increase slurry density include:

(a) Hematite

(b) Ilmenite

(c) Barite

(d) Sand


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EXAMPLE 3.5 : Use hematite to increase the density of

cement to 17.5 lbm/gal. If the water requirement are 4.5

gal/94 lbm class H cement and 0.36 gal per 100 lbm

hematite compute the amount of hematite that should be

blended with each sack.

Solution:

Assume X = lbm of hematite / sack of cement Total water requirement of slurry = 4.5 + .0036 X

X = 18.3 lbm hematite / sack of cement

volumetotal

masstotal

)0036.05.4()34.8(02.5)34.8(14.3

94

)0036.5.4(34.8945.17

XX

XX


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3.4.2 Bentonite

Use for building drilling fluid viscosity.

Also used extensively as an additive for lowering

cement density.

The addition of bentonite lowers the slurry densitybecause of its lower specific gravity and because

its ability to hydrate permits the use of much

higher water concentration.

In addition to lowering slurries density, the

addition of bentonite lowers slurry cost.


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3.4.3 Diatomaceous

A special grade of diatomaceous earth is used in

portland cements to reduce slurry density.

Lower specific gravity than bentonite.

Permits higher water/cement ratios without

resulting in free water.


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3.4.7 Hematite

Reddish iron oxide core (Fe2O3) having s specific

gravity of approximate 5.02.

Can be used to increase the density of a cement

slurry to as high as 19 lbm/gal.

The water requirement for the hematite is

approximately 0.36gal/100 lbm hematite.


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3.4.9 Barite

Barite or barium sulphate is extensively used for

increasing the density of a cement slurry.

Water requirement for barite is about 2.4 gal/100

lbm of barite.

The large amount of water required decreases the

compressive strength of the cement and dilutes the

other chemical additives.


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3.4.10 Sand

Sand having low specific gravity of about 2.63,sometimes used to increase slurry density.

Sand requires no additional water to be added to

the slurry. Has little effect on the strength or pumpability of

the cement, but causes the cement surface to berelatively hard.

Also used to form a plug in an open hole as a basefor setting a whipstock tool used to change thedirection of the hole.


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3.4.11 Setting Time Control

The cement must set and develop strength before

drilling activities can be resumed.

Compressive strength = 500 psi common

Tensile strength = 40 psi common

For shallow, low temperature wells it may be necessary

to accelerate the cement hydration so that the waiting

period after cementing is minimized.


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Commonly used accelerators:

1. Calcium chloride (upto 4.0% T < 125oF)*

2. Sodium chloride (upto 5%) **

3. Hemihydrate form of gypsum (T=low)

4. Sodium Silicate (upto 7%)

Cement setting time is also a function of:

Cement composition Fineness Water content

Increases compressive strength (generally) at

saturations > 5% it acts as retarders used to cementsalt and shale formations.

NaCl, CaCl2, MgCl2, at concentrations present in sea

water all act as accelerators.

At T > 160

o

F use retarders when using sea water.


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3.4.12 Calcium Chloride

Concentration up to 4% by weight commonly is

used as a cement accelerator in wells having

bottomhole temp < 125oF.

Available in regular grade (77% calcium chloride)and an anhydrous grade (96% calcium chloride).

Anhydrous grade is in more general use because it

absorbs moisture less readily and is easier tomaintain in storage.


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3.4.13 Sodium Chloride

An accelerator used in low concentration.

Max. accelerator occurs at a concentration of

about 5% (by weight of mixing water) for cements

containing no bentonite.

Saturated sodium chloride cements are used

primarily for cementing through salt formations

and through shale formation that are highlysensitive to fresh water.


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3.4.16 Retarders:

Deflocculants ( lignosulfonates)

(thinners, dispersants)

Halliburton (HR-12)

Borax

CM HEC


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3.4.18 Filtration Control Additives

Functions:(1) Minimize hydration of formations containing

water-sensitive shales.

(2) Prevent increases in slurry viscosity.

(3) Prevent formation of annular bridges which canact as a packer to remove hydrostatic pressureholding back high pressure zones.

(4) Reduce rate of cement dehydration when pumping intoabandoned perforated intervals allowing longer plugs.

Commonly used:

Latex Bentonite with a dispersant CMHEC Various organic polymers, such as Halliburton HALAD-9


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EXAMPLE 3.6

Bil = 17 in OD = 13.375 in. csgID = 12.415 in csgDepth = 2500 ft

high strength cement column at bottom = 500 ft

composed of class A cement + 2% CaCl2.

upper 2000 ft low density slurry class A cement + 16%

bentonite + 5% sodium chloride

Water cement ratio = 13 gal/sack

Excess factor = 1.75

Compute the slurry volume and number of cement sacks.

Annular capacity

sftin

ft 22

222

6006.4.14)375.1317(4

SLURRY DESIGN


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Volume of slurry required = 2000 (.6006) (1.75)

= 2102 cu. Ft.

Calculate the yield of cement

=

For Lead (low strength)= Volume of one sack of cement (A) + Volume of added

bentonite per sack (B) + Volume of salt water per sack (C)

cementofsack

slurryofftcu ..

sack

f t

f tlbm

sacklbmwt

awcv

3

3 4797.0/)4.62(14.3

/9494

)(

sack

f tBentoniteofwtb

bentonite

3

0910.0)4.62(65.2

)94)(16(..)(


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(c) =Volume of water = Wt. Of 5% NaCl

= .05 (94) = 4.7 lbm

Water- cement ratio = 13 gal/sack

Water wt. = 13 g.(8.34 ppg)/sack

= 108.4 lbm/sack

Wt. of fraction of NaCl =

From Table 2.3, NaCl = 1.0279 by interpolation

Volume of salt water

Yield = 0.4797 + 0.0910 + 1.7633 = 2.334 cuft/sack

No. of sack = 2102 cuft/2.334 cuft/sack = 901 sacks

0415.07.44.108

7.4

sack

ftwaterofwt

salt

2

768.1)4.62(0279.1

7.44.108

)4.62.(

.


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High strength tail slurry volume

= (.6006) (500) (1.75) +

= 559.2 cuft

Yield = volume/sack

Volume = vol. of cement (one sack) + Vol. of CaCl2

Cement Volume

Wt. of CaCl2 = (0.02) (94) = 1.88 lbm

Wt. Water = (5.2) (8.34) = 43.4 lbm

Wt. Fraction =

144

40)45.12(

4

2

sackft /4797.0)4.62)(143(

94 3

0415.04.4388.1

88.1


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By interpolation from Table 2.4

Volume of salt water (Brine)

Yield = 0.4797 + 0.7025 = 1.182 cuft/sack

No. of sacks of cement sack of cement

Total slurry volume = 2102 + 559.2 = 2661.2 cu.ft.

Total no. of sack of cement = 901 + 473

= 1,374 sacks Answer

0329.12CaCl

7025.0)4.62(0329.1

88.14.43

473182.1

2.559


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Cement Casing Conventional

Equipment:

guide shoe float collar bottom plug top plug

Outside casing: centralizers scratchers cement basket

SUB-SURFACE CASING EQUIPMENT


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Common Cement Placement Requirements.


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Conventional Placement Technique

used for cementing casing


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Guide Shoe (Courtesy World Oils Cementing Handbook)


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Float collar (Courtesy World Oils Cementing Handbook)


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Centralizers: (a) Bow springs welded on end rings (b) centralizer with

reflector vanes (c) slim-hole centralizer(Halliburton Sales and Service Catalog)


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(a) Rotating and (b) reciprocating wall scratchers

(Courtesy World Oils Cementing Handbook)


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Cement baskets (a) in place within the casing and (b) with

limit rings(Courtesy World Oils Cementing Handbook)


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Cementing plugs: (a) top and (b)bottom plugs(Courtesy World Oils Cementing Handbook)


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Different cementing placement techniques are used for:

Cementing casing strings Cementing liner strings Setting cement plugs Squeeze cementing

3.5.2 Stage Cementing

To avoid fracturing formations by reducing cement column

length.

To make sure cement is not lost in low-pressure highly

permeable zones.

3.5.3 Inner-String Cementing

To reduce cementing time and amount of cement left in the

shoe joint of large diameter casing.

Performed using drill pipe or tubing.

3.5 CEMENT PLACEMENT


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3.5.4 Annular-Cementing through tubing:

It is used to bring cement top of the previously placedcement to the surface

Or to repair casing.

3.5.5 Multiple String Cementing

It is a multiple completion method that involves

cementing several strings of tubing in the hold withoutthe use of an outer casing strings.

3.5.6 Reverse-Circulation Cementing

It is used when extremely low-strength formation werepresent near the bottom of the hole.

The cement is displaced (pumped) down the annulusand the mud is displaced back through the casing.


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3.5.7 Delayed-Setting Cementing

It is used to obtain a more uniform mud displacement. Use retarded cement slurry having good filtration property

in the well bore before running the casing.

Cement placement is achieved (accomplished) down the

drill pipe and up the annulus. The drill pipe is then removed and casing is lowered to the

unset cement.

3.5.8 Cementing liners

Latch-down plug separator mud from cement.

When it reaches top of liner it actuates a special wiper

plug.


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When wiper-plug reaches the float collar a pressure

increase at the surface signifies the end of the cementdisplacement.

Liner setting tool are activated by:

1. mechanical device (drill pipe rotated and lowered)

2. hydraulic device : drill pipe rotated or a ball or a

plug is dropped and then set by applying pressure.

Tie-back liner = to the top. Stub-liner = up the liner but not to the top = to repair leak

at liner top.


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3.5.9 Plug Cementing

Prevent fluid communications between an abandonedlower portion of the well and the upper part of the well.

Placed using drill pipe or tubing.

Bridge plug is used to assist in forming a good

hydraulic seal.

Documents

Chapter5 New (Cementing)[1]