The document discusses cement used in oil and gas wells. It covers cement composition, classes of cement, additives for controlling density, acceleration, retardation and viscosity. It also discusses cementing operations, equipment and performing a good cementing job. Key factors include casing centralization, pipe movement, drilling fluid viscosity, hole condition and achieving proper displacement velocity.

1. JAMES A. CRAIG

2. 
Cement Composition

API Classes of Cement

Cement Additives

Density control

Accelerators

Retarders

Viscosity control

Types of Cementing

Cementing Operation

Cementing equipment

Cementing process

Performing a good cementing job

3. 
Cement is made of limestone and clay/or shale mixed in the right proportions

Cement (oxides of Ca, Al, Fe, and Si) is heated in a rotary kiln to between 2,600 oF to 2,800 oF.

The result from the kiln is called Clinker.

Clinker is ground with a controlled amount of gypsum (CaSO4.2H2O) to make Portland cement.

Gypsum retards setting time and increases ultimate strength.

4. Clinker

6. 
The classes used today are primarily Classes A, C, G, and H.

Classes A, B, and C are used for surface casing job.

Class A is used in some areas because it is very similar to construction cement and can be obtained locally.

Classes A and C are already ground with an accelerator.

Classes G and H are basic cements.

Class G is a finer grind and requires more mix water resulting in a lower density.

Class G is more common around the world.

Classes E and F are used for deep wells under high temperature and pressure.

7. 
Cement additives will be sub-divided into these functional groups:

Density control

Accelerators

Retarders

Viscosity control

Others

8. 
Density of cement should be high enough to prevent the high-pressured formations from entering the well.

Density of cement should not be so high as to cause fracture of the weaker formations.

Density of normal slurry (cement mixed with normal amount of water) is usually too high for formation strength.

It is desirable to lower slurry density by:

Lowering slurry density reduces cost.

9. 
Methods of lowering slurry density:

Increase water/cement ratio

Add low-specific-gravity solids

Effect of high (excess) water/cement ratio:

Increase thickening time

Increase free water

Reduces compressive strength

Lowers resistance to sulfate attack

Increases permeability of the set cement

10. 
Common low-specific-gravity solids in use are:

Bentonite

Diatomaceous earth

Solid hydrocarbons

Pozzolan

Expanded perlite

Bentonite

Most common light-weight additive

Ability to hydrate permits the use of high water concentration.

High amount will reduce cement strength and thickening time.

Cement strength retrogress with at high temperature above 230 oF.

11. 
Diatomaceous earth (Diacel D)

Lower specific gravity than bentonite

Permits higher water/cement ratios without resulting in free water.

Like in bentonite, high amount will reduce cement strength and thickening time.

More expensive than bentonite.

Solid hydrocarbons

Gilsonite (lustrous asphalt) and Kolite (crushed coal)

Almost no effect on slurry thickening time.

Higher cement compressive strengths than other types of low-density solids.

12. 
Pozzolans

Siliceous and aluminous materials that react with lime and water to a form a calcium silicates that possesses cementitious properties.

Natural pozzolans are volcanic ash

Artificial pozzolans include glass, furnace slag and fly ash (residue from chimneys of coal-burning power plants.

Only slight reduction in slurry density is achieved.

Perlite

Volcanic glass bubbles that has sometimes been used in geothermal wells because of its insulating properties.

Considerably more expensive

13. 
If there is need for higher slurry density, additives that are used are:

Hematite

Reddish iron oxide ore (Fe2O3)

Very common because of its high specific gravity (5.02)

Barite

Barium sulfate

For smaller increases in density

Requires more water to keep slurry pumpable

Sand

Additional water not needed to be added to the slurry

Little effect on strength and pumpability of the cement

14. 
Accelerate cement hydration

Decrease thickening time

Applicable for shallow, low-temperature wells.

They are inorganic compounds:

Calcium chloride

Sodium chloride

Gypsum

Little amount is needed. If in excess, it will retard the cement.

In offshore drilling: NaCl, CaCl2, MgCl2in seawater act as accelerators.

15. 
Calcium chloride

Used in concentration of up to 4%

Anhydrous type is preferable because it absorbs moisture less readily

Sodium chloride

Best result is achieved at a concentration of 5%

Saturated type are used in salt formations or reactive shale formations.

Gypsum

Special grade of gypsum hemihydrate cement is mixed with portland cement.

Maximum working temperature is 140 oF for the regular grade, and 180 oF for the high-temperature grade.

16. 
Also called thinners or dispersants

Increase the thickening time of cement

Applicable for deeper, high temperature wells.

Are typically organic compounds

Lignins

Borax

Sodium chloride

Cellulose derivatives

17. 
Lignins

Calcium lignosulfonate

Most common retarder

Very low concentration is needed

Organic acids can be added for high temperature jobs

Borax

Sodium tetraborate decahydrate

Sodium chloride

At high concentrations

Cellulose derivatives

CMHEC (carboxylmethyl hydroxyethyl cellulose)

Commonly used

Works with all portland cements

18. 
High slurry viscosity will:

Increase pump horsepower

Increase annular frictional pressure loss, which may lead to formation fracture.

Common viscosity-control additives are:

Organic deflocculants (e.g. calcium lignosulfonate)

Sodium chloride

Certain long-chain polymers

19. 
Silica flour –to form stronger, more stable, and less permeable cements at high temperature.

Hydrazine–oxygen scavenger to control corrosion.

Radioactive tracer –to determine where cement has been placed.

Nylon–to make cement more impact resistant

Paraformaldehydeand sodium chromate –to counter the contamination effect of organic deflocculants from drilling muds.

20. 
Primary cementing

Casing cementing –cementing of casing to the borehole

Liner cementing –cementing of liner. More complex than casing cementing

Secondary/remedial cementing

Plug cementing –to separate lower section of a well from upper section. Open hole or cased hole.

Squeeze cementing –to plug off abandoned perforation, repair annular leaks, and plug severe lost circulation zones.

21. 
Cementing Equipment

Cementing Process

Performing a Good Cementing Job

22. 
Cement head

23. 
Guide shoe
Guides the casing past irregularities in the borehole wall.

24. 
Centralizer
They are placed on the outside of the casing to help hold the casing in the center of the hole.

25. 
Float collar
Acts as a check valve to prevent cement from backing up into the casing.

26. 
Float shoe
Serves the function of both a guide shoe and a float collar when no shoe joints are desired.

27. 
Cement basket
Placed on the outside of the casing to help support the weight of the cement slurry at points where porous or weak formations are exposed.

28. 
Bottom plug

29. 
Top plug

30. 
Scratchers
Placed on the outside of the casing to help remove mudcake from the borehole walls, either by reciprocating the casing or by rotating the casing.

32. 
Bottom rubber wiper plug is released to minimize cement contamination from drilling fluid.

Spacer fluid (or mud preflush) may be pumped also.

Desired volume of slurry is pumped

Top wiper plug is released

Drilling fluid displaces the top plug down the casing

When bottom plug reaches the float collar, its diaphragm ruptures.

The whole cement slurry has been fully displaced when the top plug bumps the bottom plug.

34. 
Cement excess
* Note:care should be taken to ensure cement does not reach the subsea well or mudline.

35. 
Casing centralization

Pipe movement

Drilling fluid condition

Hole condition

Displacement velocity

Spacer fluids

Mud-cement density difference

Directional wells

36. 
Centralization promotes a good cementing job

Centralizers are used to keep the pipe in the center of the hole

For a non-Newtonian fluid when pipe is not well centralized, the velocity on the narrow of the annulus is slower than the velocity on the wide (Popcorn theory).

The point between the centralizers is the hardest to centralize

37. 
The degree of centralization is called % Standoff.

100% -perfectly centralized

0% -pipe touching wall

A minimum standoff of
70% is a good rule-of-thumb
() ()%Standoff1100% bcCDRR + =−×−

38. 
Rule of thumb:

1 centralizer per 2 joints in vertical wells.

1 centralizer per 1 joint in directional wells

2 centralizers per 1 joint in high angle or horizontal wells.

Smaller hole clearance will require more centralizers

39. 
Pipe movement is rotation and/or reciprocation.

It increases the displacement efficiency

Drag forces associated with rotation will pull the cement into the narrow side of the annulus.

40. 
Reciprocation has a tendency to break the gel strengths of the mud in the narrow side of the annulus.

The pipe should be reciprocated from the time the pipe reaches bottom until the cement plug bumps.

Pipe sticking may be a problem

Landing the casing if it starts to stick

41. 
Higher viscosity mud is harder to displace

Viscosity of mud can be reduced prior to cementing by adding water (or thinners in a weighted mud).

Move the casing

The thicker the mud, the longer it should take to circulate.

42. 
A clean hole allows the ease of running casing and getting centralizers to bottom.

Washouts are hard to cement

If washouts are a problem, change the mud to try and minimize the washouts.

43. 
Which should be employed: turbulent, laminar or plug flow?

44. 
Laminar flow:

Has the smallest displacement efficiency (75% and less).

Laminar flow gives inadequate cementations and should be avoided when possible since it promotes channeling

Plug flow:

Lowest annular velocity (30 to 90 feet/min, depending upon cement properties).

Very efficient

Limited to cementations of small volumes and where the mud in the hole is of low density.

Can be used when high displacement rate is possible because of ECD or hole size.

45. 
Turbulent flow:

High displacement efficiencies.

Applicable to large volume cementations

Applicable where the mud and cement slurry weight are similar.

Limited in use by excessive bottomhole circulating pressure.

Can be limited by insufficient surface pump horsepower.

Primarily chosen because it requires shortest of all cementation times.

46. 
Cement and mud are not compatible and should be kept separate.

A spacer fluid is used to separate the cement and mud in the annulus.

The spacer fluid should compatible with both cement and the mud

The spacer volume should equal at least 500 ft in the annulus.

47. 
In water based muds (WBM), water is a very good spacer

Water is thin and will easily go into turbulent flow

Compatible with both cement and mud

Cost effective

In weighted muds, spacer may have to be weighted with barite.

48. 
Little effect on displacement efficiency

The cement should be at least 0.5 ppg greater than mud density to prevent movement after the pump stops

49. 
Difficult to get adequate centralization

Cuttings bed

There may be cuttings
beds on the bottom of
the hole.

They should be removed
before cementing.

50. 
Free water

Should be zero to
minimize the possibility
of a free water channel
on the high side of
the hole.

51. 
Data:

Casing setting depth, HTVD= 3,000 ft

Average hole size, Dh= 17-1/2 in.

Casing ID, DCID= 12.615 in.

Casing OD, DCOD = 13-3/8 in.

Float collar (from shoe), HFC = 44 ft

Pump factor, Fp= 0.112 bbl/stroke

Casing program:LEAD (or FILLER)TAIL (or NEAT)
Density (ppg)13.815.8
Height (ft)2,0001,000
Yield (ft3/sack)1.591.15
Excess volume = 50%

52. Questions:

How many sacks of LEAD cement will be required?

How many sacks of TAIL cement will be required?

How many barrels of mud will be required to bump plugs?

How many strokes of pump will be required to bump plugs?

53. 22Annular capacity,C183.35hCODADD− = 2217.513.375183.35− =30.6946 ft/ft= Determine number of sacks of LEAD: Excess# SacksyieldACh××=0.69462,0001.501.59××=1,311 sacks= 2Casing capacity,C183.35CIDCD= 212.615183.35=30.8679 ft/ft= 2Casing capacity,C1,029.4CIDCD= 212.6151,029.4=0.1545 bbl/ft=

54. Determine number of sacks of TAIL: Excess# Sacks (annular) yieldACh××=0.69461,0001.501.15××=906 sacks= # Sacks (casing) yieldAFCCH×=0.8679441.15×=33 sacks= # Sacks (total) (annular) (casing)=+90633=+939 sacks=

55. Determine barrels of mud to bump plugs: ()VolumeTVDFCCHHC=−×()3,000440.1545=−×456.7 bbls= Determine number of strokes to bump plugs: Volume# StrokesPF=456.70.112=4,078 strokes=