1. DRILLING ENGINEERING
Cementing

2. CEMENTING The purposes of this chapter are to present:
1. The primary objectives of cementing
2. The test procedures used to determine if the cement slurry and set-cement have suitable properties for meeting those objectives.
3. The common additives used to obtain the desirable properties under various well conditions.
4. The techniques used to place the cement at the desired location in the well.

3. TYPES OF CEMENT 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 the Klin (2600 – 2800 oF).
When it cools, it becomes balls of cement clinker.
After aging in the storage, the seasoned clinker is taken to the 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.

4. 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.

5. Manufacturing of Portland Cement

6. 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 of the 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.

7. 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

9. Well depth and cementing time relationship used in definition of API cement classes.

10. Physical Requirement of API Cement Types.

11. Normal Water Content Of Cement Recommended by API

12. For each wt% of barite added 0.2% of water should be added.
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 = sq.in.

13. PROPERTIES OF CEMENT 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.

14. 3.4 CEMENT ADDITIVE
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.

15. 3.4.1 Density Control:
The density of the cement slurry must be high enough to prevent 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 cement ratio, or adding low specific gravity solids, or both.

16. Low specific gravity solids used to reduce slurry density include:
1. Bentonite
2. Diatomaceous earth
3. Solid hydrocarbons
4. Expanded perlite
5. Pozzolan
Slurry density usually is increased by using a lower water content or adding high specific gravity solids. High specific gravity solids used to increase slurry density include:
(a) Hematite
(b) Ilmenite
(c) Barite
(d) Sand

17. EXAMPLE 3. 5 : Use hematite to increase the density of cement to 17
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 = X
X = 18.3 lbm hematite / sack of cement

18. 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 density because 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.

19. 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.

20. 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.

21. 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.

22. 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 be relatively hard.
Also used to form a plug in an open hole as a base for setting a whipstock tool used to change the direction of the hole.

23. 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.

24. 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 cement salt and shale formations.
NaCl, CaCl2, MgCl2, at concentrations present in sea water all act as accelerators.
At T > 160oF use retarders when using sea water.

25. 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 to maintain in storage.

26. 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 highly sensitive to fresh water.

27. 3.4.16 Retarders: Deflocculants ( lignosulfonates)
(thinners, dispersants)
Halliburton (HR-12)
Borax
CM HEC

28. 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 can act as a packer to remove hydrostatic pressure holding back high pressure zones.
(4) Reduce rate of cement dehydration when pumping into abandoned perforated intervals allowing longer plugs.
Commonly used:
Latex
Bentonite with a dispersant
CMHEC
Various organic polymers, such as Halliburton HALAD-9

29. SLURRY DESIGN EXAMPLE 3.6 Bil = 17 in OD = 13.375 in. csg
ID = in csg
Depth = 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

30. 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)

31. (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
= lbm/sack
Wt. of fraction of NaCl =
From Table 2.3, NaCl = by interpolation
Volume of salt water
Yield = = cuft/sack
No. of sack = 2102 cuft/2.334 cuft/sack = 901 sacks

32. High strength tail slurry volume
= (.6006) (500) (1.75) +
= 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 =

33. By interpolation from Table 2.4
Volume of salt water (Brine)
Yield = = cuft/sack
No. of sacks of cement sack of cement
Total slurry volume = = cu.ft.
Total no. of sack of cement =
= 1,374 sacks Answer

34. SUB-SURFACE CASING EQUIPMENT
Cement Casing Conventional
Equipment:
guide shoe
float collar
bottom plug
top plug
Outside casing:
centralizers
scratchers
cement basket

35. Common Cement Placement Requirements.

36. Conventional Placement Technique used for cementing casing

37. Guide Shoe (Courtesy World Oil’s Cementing Handbook)

38. Float collar (Courtesy World Oil’s Cementing Handbook)

39. Centralizers: (a) Bow springs welded on end rings (b) centralizer with reflector vanes (c) slim-hole centralizer (Halliburton Sales and Service Catalog)

40. (a) Rotating and (b) reciprocating wall scratchers (Courtesy World Oil’s Cementing Handbook)

41. Cement baskets (a) in place within the casing and (b) with limit rings(Courtesy World Oil’s Cementing Handbook)

42. Cementing plugs: (a) top and (b)bottom plugs
(Courtesy World Oil’s Cementing Handbook)

43. 3.5 CEMENT PLACEMENT
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.

44. 3.5.6 Reverse-Circulation Cementing
3.5.4 Annular-Cementing through tubing:
It is used to bring cement top of the previously placed cement 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 without the use of an outer casing strings.
3.5.6 Reverse-Circulation Cementing
It is used when extremely low-strength formation were present near the bottom of the hole.
The cement is displaced (pumped) down the annulus and the mud is displaced back through the casing.

45. 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.

46. When wiper-plug reaches the float collar a pressure increase at the surface signifies the end of the cement displacement.
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.

47. Plug Cementing
Prevent fluid communications between an abandoned lower 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.