ch 4 well cementing_part 1

8/18/2019 Ch 4 Well Cementing_part 1

1/34

C

WELL CEMENTINGBy: ASIF ZAMIR

Petroleum Engineering Department

Universiti Teknologi PETRONAS, Malaysia

2016


2/34

Learning Outcome

• To evaluate between primary and secondary cementingfunctions and areas of applications.

• To review the API classifications of well cement and their applications

• To perform detailed well cementing calculations based oproperties of cement slurries


3/34

Introduction

• Oil and gas well cementing is probably the most important operationdevelopment.

• The drilling team is usually responsible for cementing the casings and

•

The quality of these cementing operations will affect the success of fdrilling, completion, production and workover efforts in the well.

• Oil and gas well cementing can be grouped into two: (1) Primary cei.e., cementing the casings and liners (2) Secondary or remedial cemi.e., squeeze and plug cementing.


4/34

• Primary cementing refers to the cementing ofcasing and/or liner strings to surroundingformation. The functions of primary cementingare as follows:

1. To support vertical and radial loads applied to casing

2. To isolate porous formations from producing zoneformations

3. To exclude unwanted subsurface fluids from theproducing interval

4. To protect the casing from corrosion fluids in theformation

5. To confine abnormal formation pressures

Primary Cementing & Functi


5/34

• The functions of primary cementing to specificcasing and liners are as follows:

1. Conductor casing: cementing prevents the drillingfluid from escaping and circulating outside thecasing

2. Surface casing: cementing protects fresh-waterformation

3. Intermediate casing: cementing seals off abnormalpressure formations

4. Production casing: cementing prevents producedfluids from migrating to nonproducing formations

Primary Cementing & Functions C


6/34


7/34

b) Plug cementing: plug cementing are used for various reasons includfollowing:

1. Plug-off abandoned wells by sealing off selected intervals, dry hole owell

2. Solving lost circulation problem by spotting a cement plug across thand then drilling back through the plug

3. Sidetracking or to initiate directional drilling to help guide the bit in thdirection.

4. Provide an anchor for an open-hole test, particularly when the zonetested is significantly off bottom.

Secondary Cementing & Functions


8/34

Plug cementing examples:

Secondary Cementing & Functions

Lost circulation plug Abandonment plug Side tracking plug Open-hole


9/34

Well Cementing Materials

• Well cementing materials vary from basic Portland cement to sophistresin-based or latex cement.

• Cement is made of calcareous and argillaceous rock materials that usually obtained from quarries.

• The calcareous materials contain calcium carbonate or calcium oxidwhereas the argillaceous materials contain clay or clay minerals.

• These materials are ground, mixed and subjected to high temperatu


10/34

Well Cementing Materials Co

( C a l c a

r e o u s M a t e r i a l s ) Limestone

Cement rock

Chalk

Marl

Alkali waste

( A r g i l l a c e o u s m a t e r i a l s ) Clay

Shale

Slate

Ash

( C e m e n t ) Gri

+

M

+

HigTempe


11/34

The American Petroleum Institute (API) classifies well cement into nine

Classifications of Well Ceme

Class A Applicable from surface to 6,000 ft. depth. No special properties are rClass B Applicable from surface to 6,000 ft. depth. For moderate to high sulph

Class C Applicable from surface to 6,000 ft. depth. For high early strength. Avamoderate & high sulphate resistant types.

Class D Applicable from 6,000 to 10,000 ft. depth. For moderately HPHT wells. Amoderate & high sulphate resistant types.

Class E Applicable from 10,000 to 14,000 ft. depth. For HPHT wells. Available in

& high sulphate resistant types.

Class F Applicable from 10,000 to 16,000 ft. depth. For extreme HPHT wells. Avmoderate & high sulphate resistant types.

Class G & HApplicable from surface to 8,000 ft. depth. Can be modified with addwide range of depths and temperature. Available in moderate & highresistant types.

Class J Applicable from 12,000 to 16,000 ft. depth. For extreme HPHT wells. Cawith additives to cover wide range of depths and temperature.


12/34

Sulphate minerals are abundant in some formation waters that can cocontact with set cement.

These minerals include magnesium, calcium and sodium sulphate whiclime in the set cement.

Calcium sulphate reacts with the tricalcium aluminate component of tform sulfoaluminate.

This reaction causes expansion and ultimately disintegrates the set cem

To increase the cement resistance to sulphate attack, the amount of traluminate and free lime in the cement should be decreased.

Effect of Sulphate Minerals to Well C


13/34

Properties of API Cement Cla

• Table 1 below gives the basic properties of the various classes of dry API cem


14/34

Properties of Cement Slurry & Set C1. Specific Weight:

This is one of the most important properties of a cement slurry. A neat cemen

combination of only cement and water.The specific weight of a neat cement slurry is defined by the amount of wate

with the dry cement, that is, water-to-cement ratio.

Table 2 below gives the maximum and minimum water-to-cement ratios and tresulting neat slurry specific weight (lb/gal) and specific volume (ft3/sk) or yieldthree API cements

l


15/34

Specific Weight, Absolute Volume Specific Weight:

the specific weight of a cement slurry is expressed as:

Absolute volume:

For powdered materials that are additives to cement slurries, the absolute vo

Yield:

This is defined as the volume of slurry that results from 1 sk of cement additive

(/) = / + / + (/)

/ + / + (/)

. (/) = (/)

8.34 / .

(/) = / + / + (/)

7.48 /


16/34

Example 1

Calculate the specific weight and yield for a neat

of Class A cement using the maximum permissibleto-cement ratio.

(/) = / + / + (/)

/ + / + (/)

. (/) = (/)

8.34 / .

(/) = / + / + (/)

7.48 /


17/34

Specific Weight of Cement SIt is often necessary to decrease the specific weight of a cement slurry to av

fracturing weak formations during cementing operations.

There are basically two methods of accomplishing lower specific weights wh

1. Adding clay or chemical silicate type extenders together with extra water.

2. Adding large quantities of pozzolan, ceramic microsphere or nitrogen.

Similarly, it may also be necessary to increase the specific weight of cementparticularly when cementing through high-pressure formations. These include

1. Using the minimum permissible water-to-cement and adding dispersants tothe fluidity of the cement slurry

2. Adding high-specific-gravity materials to the cement slurry together with opslightly reduced water-to-cement ratio for the particular cement class.


18/34

Thickening TimeIt is important that the thickening time for a given cement slu

known prior to using the slurry in a cementing operation.

When water is added to dry cement and its additives, a chereaction begins that results in an increase in slurry viscosity.

When the slurry viscosity becomes too large, the slurry is no lo

pumpable.

Thus if the slurry is not placed in its proper location within the wthe slurry becoming unpumpable, the well and the surface eqcould be seriously damaged.


19/34

Thickening Time Cont’d.Thickening time is defined as the time required for the cement slurr

maximum pumpable viscosity.

This thickening time must be considerably longer than the time reqout the actual cementing operation.

Retarders such as lignosulphonate, cellulose derivatives, and sugarincrease the thickening time of cement slurry.

Accelerators, such as calcium chloride and sodium chloride are hoadded to decrease the thickening time of cement slurry. This is necearly compressive strength of cement is needed. Mostly applicablesurface casing string cementing and directional drilling plugs.


20/34

Cementing Operation TimThe cementing operation time is the total time required for th

slurry to be placed in the well.

Usually a safety factor (SF) is added to this estimate, where ais added for shallow operations while 2hr SF is added to deepoperations.

The cementing operation time is given by:

= time required to mix the dry cement (and additives) with w

= time required to displace cement slurry by mud inside the

= plug release time (hr)

= safety factor of 0.5 to 2 hr.

= + + +


21/34

Cementing Operation Time CoMixing Time:

Displacement Time:

The cement slurry chosen must have a thickening time greaterestimated time for the actual cementing operation, i.e, >

= = ()

(/) × 6

=

=

(

(


22/34

Example 2

The minimum thickening time is required for a primary cementi

operation to cement a long intermediate casing string. The intecasing string is a 9-5/8 in. (ID=8.535 in.), 53.5-lb/ft casing set in ahole. The casing string is 12,000 ft long from the top of the floatsurface. The cementing operation will require 1,200 sacks of Clcement. The mixing capacity of the single cementing truck is 2minute. The rig duplex mud pump has an 18-in., stroke (2.5-in ro

1/2 in., liners, and will be operated at 50 strokes per minute withvolumetric efficiency. The plug release time is about 15 minuteabove field cementing operation, evaluate the minimum thickassuming a safety factor of 1 hr.

To be solved in class>>>>>


23/34

Strength of Set CementA properly designed cement slurry will set after it has been pl

appropriate location within the well.

Cement strength is the strength the set cement has obtainedrefers to compressive strength or tensile strength.

For most well applications, cement having a compressive stre

psi (35 bar) is considered adequate.

The compressive strength of cement is dependent on water-ratio of slurry, curing time, temperature and pressure during cadditives in the cement.


24/34

Strength of Set Cement Con

In cement compressive strength test, four or five samples of c

cubes are allowed to cure for a specified period of time.

The cement cubes are placed in a compression testing maccompressive strength of each sample cube is obtained expe

The average value of the samples is obtained and reported acompressive strength of the cement.


25/34

Strength of Set Cement Con

Influence of Time and Temperature on Compressive Strength o

Cement


26/34

Cement Shear ForceIn shear bond strength test, the cement slurry is allowed

to cure in the annulus of two concentric steel cylinders.

After curing, the shear force required to break thebond between the set cement and one of the cylinders(usually the inner cylinder) is obtained experimentally.

This shear force can be expressed as:

Where = compressive strength (psi); = outsidediameter of casing (inch); ℎ= height of the cementcolumn (inch)

= 0.969ℎ


27/34

Example 3

Design the total weight that can be supported by the Class H s

bonded to a 9-5/8 in. (8.535 in) casing string, 53.5 lb/ft and hole1/2 in. The cement operation will require 1,200 sacks of cemenyield of 1.05 ft3/sk. There are 120 ft of casing below the float coa compressive strength of 500 psi.

= 0.969ℎ


28/34

Cement Additives

Cement additives are chemical additives that are used to a

basic properties of the neat cement slurry and its resulting set

Cement additives can be divided into six (6) functional group

1. Specific weight control

2. Thickening and setting time control

3. Loss of circulation control4. Filtration control

5. Viscosity control

6. Special problems control


29/34

Cement Additives Cont’d

Specific weight control additives:

These additives are required to lower/increase the specific weight of cemeformation damage. They include:

1. Bentonite

2. Diatomaceous earth

3. Solid hydrocarbons (e.g. asphaltite and coal)

4. Expanded perlite

5. Pozzolan

6. Hematite

7. Ilmenite

8. Barite

9. Sand


30/34


Thickening and setting time control additives:

These additives are required to either accelerate, or retard the thickening atime of cement slurry. They include:

1. Calcium Chloride (accelerator)

2. Sodium chloride (accelerator)

3. Sodium silicate (accelerator)

4. Gypsum (retarder)


31/34


32/34


Viscosity control additives:

These additives are required to lower the viscosity of the cement slurry to enpumpability of the slurry. They include:

1. Calcium lignosulfonate

2. Sodium chloride

3. Long-chain polymers


33/34

Example 4A specific weight of 17.1 lb/gal is required for a Class H cement slurry. It is decidecement be mixed with sand in order to increase the specific weight of the slurry. weight of sand (in lb/sk) that should be added with each sack of cement. Assum

gravity of sand to be 2.63 and weight of water is 8.34 lb/gal. Refer to the tables binformation.

(Lb/gal) (ft3/sk)

(/) = / + / + (/)

/ + / + (/)

. (/) = (/)

8.34 / .


34/34

End of Presentation

ch 4 well cementing_part 1

Documents