Petroleum Engineering, Drilling Engineering, Primary Cementing

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=