A General Overview of the Cementing Process of Oil-Wells

Presented byAung Thet TunHan Myint HtunHtet Naing HtooYan Paing Htwe

Contents• Introduction to Cementing

– Description of cementing– Importance of cementing– Cement types and their usage– Additives types and their usage

• Cementing Equipment and Casing Hardware• Cementing Techniques

– Primary Cementing– Remedial Cementing

• Laboratory Testing, Evaluation and Analysis of Well Cements– Performance Evaluation

• Common Accidents in Cementing Process• Conclusion

Introduction

• It is the process by which cement slurry is placed in the annulus ,bonding the casing to the formation.

• Conventionally the cement is pumped

down the casing and displaced around

the shoe into the annulus.

• Cement is made limestone and clay or shale mixed in the right proportion.

• The cementing process involves mixing a cement slurry composed of dry powdered cement, water and chemical additives used to control the cement properties.

• Cement is a non-Newtonian fluid and is shear thinning similar to mud.

Process of Portland Cement

Grind+Heat

(+1500.C) Cooling Mix

Clinker Gypsum Portland Cement

1(Clay, Shale, Slate,Mud stone, Ashes) 2(Calcium Carbonate, Cement rock, Chalk, Marl, Marine(limestone)) Cement Clinker(Tricalcium Silicate, Dicalcium Silicate, Tricalcium Aluminate, Tetracalcium

Aluminoferrite) (C3S, C2S, C3A, C4AF)

Gypsum (CaSO4.2H2O) or Blend of Gypsum +Plaster

1 2

Why should cement job needed for every wells?

Provide support to the casings Zonal isolation-prevent fluid movement between zones Casing protection against corrosive fluids Protect water zones

• Cementing operations can be divided into two broad categories: primary cementing and remedial cementing.

• Remedial cementing operations consist of two broad categories: squeeze cementing and plug cementing.

Type of CementClass Depth (ft) Temperature (.F)

A 0-6,000 80-170

B 0-6,000 80-170

C 0-6,000 80-170

D 6,000-10,000 170-290

E 10,000-14,000 170-290

F 10,000-14,000 170-290

G All depths

H All depths >230

J All depths >230

API Class C3S % C2S% C3A% C4AF% CaSo FinenessSqcm/Gram

A 53 24 8 8 3.5 1600-1900

B 44 32 5 12 2.9 1500-1900

C 53 16 8 8 4.1 2000-2400

D & E 50 26 5 13 3.0 1200-1500

G 52 27 3 12 3.2 1400-1600

H 52 25 5 12 3.3 1400-1600

API Class Type

A Portland

B Portland

C High Early

D Retarded

E Retarded

F Retarded

G Basic-Calif

H Basic-Gulf Coast

• Class A– Intended to use from surface to 6000ft (1,830m)–When no special properties are required.– Cheaper than other classes of cements

• Class B– Intended to use from surface to 6000ft (1,830m)–Moderate to High sulphate resistance

– Has lower C3A content than class A

• Class C– Intended to use from surface to 6000’ (1830m)– When conditions require early strength– Available in all 3 degree of sulphate resistance

• Class D– Intended to use from surface to 6000’ (1830m) to 10,000’(3050m)– Moderate and High sulphate resistance type available

• Class E– Intended to use from 10,000’to 14,000’ (1830m to 4720m)– Under conditions of High temperature and pressure

• Class F– Intended to use from surface to 10,000’ to 16,000’(1830 to 4880m)– Moderate and High sulphate resistance types available

• Class G and H– Intended to use from surface to 8,000’ (2440m)– Can be used with accelerators and retarders to cover a wide range of well

depths and temperatures

• The classes used today are primarily Class G, H, C and A.• Class C and A are used on shallow casing strings.• Class A is used in some areas because it is very similar to

construction cement and can be obtained locally.

Cementing Additives

• Accelerators and Retarders Control thickening time• Extenders Slurry density, Slurry yield• Weighting Agents Slurry density• Dispersants Friction pressure

Accelerators• Reduce setting times of a cement system for shallow, low temperature

applications.• To reduce: WOC• Accelerators: Calcium chloride

Sodium chloride

Gypsum

Sea water• Other accelerators are

ammonium chloride

and sodium silicate.

Retarders

• Increase the thickening time of

cement for deeper, hotter

application.• Lignins, sugars, Saturated Salt

solutions, sodium chloride

(high concentration)• One of the most common

retarders

is calcium lignosufonate.• BHT is directly related retarders

Extenders

• Extenders are materials which lower the density of a cement system.• Extenders make reduce slurry density and increase slurry yield.• Extenders:

Clays Sodium Silicates Pozzolans Lightweight Particles Nitrogen

• Water Extenders: (water)– To maintain homogeneous slurry– To prevent the development of excessive free water

Gaseous Extenders : (Nitrogen or Air can be used)

Summary of ExtenderExtender Performance Features and benefits

Bentonite Assists fluid-loss control

Fly Ashes Resist corrosive fluids.

Sodium Silicates Only low percent ages required. Ideal for seawater mixing.

Microspheres Good compressive strength, thermal stability, and insulating properties.

Foamed Cement Excellent strength and low permeability.

Weighting Agengts

• Weighting Agents are materials which increase the density of a cement system.

• Weighting Agents: Ilmenite, Hematite, BariteMaterial Sp.Gr Absolute

Volume(gal/lb)Color Additional

WaterRequirement(gal/lb)

Ilmenite (FeTiO3)

4.45 0.027 Black 0.00

Hematite(Fe2O3)

4.95 0.024 Red 0.0023

Barite(BaSo4)

4.33 0.028 White 0.024

Barite(BaSo4)

DispersantsDispersants

Improve mud removal Improve cement slurry mixabilityReduced water slurriesReduce friction pressureTurbulent flow easier to achieve

(Speacially Linear)

Types of Dispersants

Sodium Polynapthalene Sulfonate

Aromativepolymer Lignin Derivative Formaldehyde family Organic polymer

Dispersants

• Dispersants are chemicals which reduce the viscosity of a cement slurry.

• Dispersants– Improve mud removal– Improve cement slurry mixability– Reduced water slurries– Reduce friction pressure– Turbulent flow easier to achieve (Speacially Linear)

Fluid Loss Control Agents

• Fluid Loss: the unwanted migration of the liquid part of the drilling mud or cement slurry into a formation.

• Fluid loss additives:Particulate Materials Water-Soluble Polymers

Lost Circulation Prevention Agents• Lost Circulation: the quantities of whole mud lost

to a formation, loss in Cavernous formation,

Natural fractures, Induced fractures and Highly

permeable formations.• Lost Circulation may be divided into four type.

Type of Loss Severity of Loss

Seepage Less than 1.6m3/hr(10bbl/hr)

Partial 1.6 to 16m3/hr (10 to 100bbl/hr)

Severe More than 16m3/hr

Total No fluid return to the surface

Lost circulation materials (LCMs):

Cottonseed hulls Shredded leather Sawdust Straw Ground walnut shells BARO-SEAL (Halliburton) BAKER SQUEEZ (Baker Hughes) for partial

loss

Three type of solving technique when Lost circulation occur

Expandable Casing Managed Pressure Drilling Casing While Drilling

Miscellaneous Cement Additives

• Antifoam Agents• Strengthening Agents• Radioactive Tracing Agents• Mud Decontaminants

Equipment

Cementing jobs are usually performed with the following equipment:1. bulk equipment for storing and mixing2. cement pumping unit3. treating irons4. mixing system5. batch mixer6. fluid tanks7. liquid additive system8. cement heads.

1.Bulk Equipment

• Required during a primary cementing job for storing the dry cement and transferring it to the cement mixing system

i. pressurized cement silos or gravity cement silosii. bulk cement transportersiii. air compressoriv. 4-in rubber hosesv. surge tankThe bulk equipment must be well maintained.

2.Cement Pumping Unit

provides the high-horsepower and pressure pumping capabilitymeters mixing fluidsprovides and controls the cement mixing systemmonitors pump rates and pressures

3.Treating Irons

• used to carry the cement slurry and other fluids pumped from the cement unit to the well

• a 2-in 1502 treating iron is used for cementing operations• the treating iron must be rigged according to the guidelines in

Well Services Safety Standard 5• strict guidelines for the use, inspection and testing of the

treating iron exist

Treating Iron

4.Mixing System

• to ensure correct proportions of dry cement and mix fluid resulting in a cement slurry with predictable characteristics

• Several different types of mixing system are used• can be found in JET Manual 7: Cement Mixing Equipment

(InTouch Content ID# 4127834)

5.Batch Mixer

• a simple operation for mixing cement slurries• range in capacity from 15 to 150 bbl• typically equipped with paddles, circulating centrifugal pumps,

and lines• allow the slurry to be circulated and mixed in batch tanks

during the mixing process• To fill the batch tank with slurry mixed on the fly at the desired

density

• to make any final adjustments in density• be careful to add the cement slowly and at a manageable rate• the density is measured at regular intervals• the slurry is allowed to homogenize before its density is

measured

6.Fluid Tanks

• Fluids used during the cementing operation must be stored and prepared in fluid tanks

• Recirculation of the slurry with the centrifugal pumps should be kept to a minimum

• Cement testing in the laboratory should reflect the fact that slurry will be batch mixed

• rig mud pits are used to store these fluids

7.Liquid Additive System

• Liquid additive storage and metering systems provide a means of storing and measuring liquid additives– manual control system: Four enclosed tanks are used to store

different liquid additives– automatic control system: The system includes a method of

controlling the metering of additives automatically

– computerized LAS system: This system includes a metering control module, electromagnetic flow meters with control valves, and a remote terminal

8.Cement Heads• Cement heads are discussed in detail in JET Manual 8: Cement Head and Casing

Hardware (InTouch Content ID# 4127832)

Auxiliary Cement Equipment

• Include – casing guide shoes– float collars– multistage collars– Centralizers– cement baskets, and – Top plug , bottom plug

Guide Shoe• The most basic form of casing

shoes

• Containing no check valves or flow-control devices

• Use to protect the lower edge of the casing

• Most types offer a rounded nose to guide the casing through doglegs or restrictions in the hole

Types of Guide Shoes

Float Collar• Collars which contain check valves to prevent wellbore fluids from entering• the float valve must prevent backflow into the casing

Centralizers

The standard welded centralizer Spiral centralizer

Cement Basket

Top Plug , Bottom Plug

• The top plug is solid and the bottom plug is hollow and has a diaphragm that ruptures when the bottom plug hits the float collar

Primary Cementing

• Primary Cementing is the placement of cement into the

annulus.Zonal isolationSeal off certain zones from other zones

Casing SupportProvide axial support for the surface casing and other casings that may be run later

Casing protectionProvides support and protection against plastic formations and corrosive formation fluids

Borehole SupportProvide support to the borehole for plastic, water-sensitive, or unconsolidated formations.

The Goal of Primary Cementing

Basic cementing procedure

1. Running Casing2. Circulating mud by rig pump3. Pressure testing4. Pumping wash and spacer5. Dropping the bottom plug6. Mixing slurry7. Pumping lead slurry8. Pumping tail slurry9. Dropping the top plug10. Displacing slurries and plugs with fluid11. Checking returns

Running casing

• The first joint of the casing run into the well has a float or guide shoe attached to the end.

• After the first or second joint, a float collar is

installed. The space between the float collar and the shoe is called a shoe track.

• When the casing string is run to the desired depth, special connections may need to be made just at the wellhead; this process is called nippling up.

Circulating mud by rig pumpMud conditioning is achieved by circulating mud down the casingand taking returns at the annulus

Mud conditioning

Condition the mud & clean the well

Caution:The mud conditioning must bedesigned with the same attention:poor design can result in channeling

Mud

Guide Shoe

Float Collar

Pressure testing

• The high-pressure treating lines running from the cement unit to the well connection must be pressure tested before the cementing process begins

1. Prime the cement unit and lines with water to fill all the lines2. Close the valve at the wellhead, and make sure no one is near the lines3. Increase the pressure to a predetermined level by having the unit pump water.4. Hold the pressure for about 5 minutes, and monitor for leaks.

Pumping wash and spacer• A chemical wash or a weighted spacer or both are typically pumped ahead of the cement slurry to act as a buffer between the cement and drilling fluid.

The chemical wash Helps thin and disperse the drilling mud in the wellbore and annulus

A spacerKeep the drilling mud and slurry separated during the displacement

process.

Chemical Wash

Spacer

Dropping the bottom plug

Wiper plugs are pumped ahead and behind the cement slurry on primary cement jobs

•Separate slurry from drilling fluids•Wipe the inside walls of the casing•Help provide a positive indication (pressure) that the cement is in place outside the casing

Bottom Plug

Mixing slurry

The cement slurry

This process can be done continuously or in a batch procedure The mix fluid (water plus cement additives) can be prepared ahead

of time or mixed on-the-fly using a liquid additive system.

Dry cementWater

Any required additives

Mixer

Pumping lead slurry• Lead slurry - a low-density,

high-yield slurry; designed to fill and cover the upper section of the annulus

• It is pumped from the cementing unit through the cement head and into the casing • When the bottom plug reaches the float collar, the plug’s diaphragm ruptures and the wash, spacer, and slurry proceed to the casing shoe.

Cement Head

Pumping the tail slurry

Tail slurry – A higher-density slurry Used to cover the lower section of the annulus up from the bottom of the hole.

Tail Slurry

Lead Slurry

SpacerWash

Tail Slurry

Lead Slurry

Dropping the top plugTop plug• Solid wiper plug• Separate and protect the slurry from contamination by the displacement fluid that will be pumped in the next step.

After the slurry has been pumped into the casing, the top plug is released from the cement head.

Pumping is stopped when the tail slurry has been pumped

The valves on the cement head are set to allow fluid—usually water or spacer—to be pumped to push the top plug out of the cement head.

Top Plug

Displacing slurries and plugs withfluids

• The cement slurries and wiper plugs are pumped down the well using either drilling fluid or another fluid.

• When the bottom wiper plug lands on the float collar, the membrane on top ofthe plug ruptures and the slurry is pumped out of the bottom of the casing and up into the annulus.

• When the top plug reaches the bottom plug, it is sealed against the bottom plug by a pressure increase

Checking returns

• The float collar contains a check valve

• At the end of a cementing job, check to ensure that the float collar or float shoe is not leaking

• This check is done by allowing fluid to flow back to the cement unit displacement tanks

• If the float collar or shoe is working correctly, 2 to 5 bbl will flow back and then stop

Remedial Cementing

• When a primary cement job objectives have not been achieved, or when the cement or casing has failed over time, it may be necessary to repair the problem.

Remedial Cementing

Squeeze cementing Plug cementing

Squeeze cementing

Cement slurry is forced through holes or splits in the casing to repair a primary cement job or a well problem.

Purposes of squeeze cementing

• Repair improper zonal isolation• Eliminate water intrusion• Repair casing leaks

Repair improper zonal isolation

• The top of the cement may be lower than designed because of losses during the primary job, inaccurate hole volume calculations, or incomplete displacement.

• The solution is to squeeze cement slurry through perforations just above the cement top to extend the cement column length in the annulus.

Perforation

Eliminate water intrusion• Unwanted water or gas from above or below the producing

zone is plugged off by perforating these zones and squeezing cement slurry through the perforations.

Squeeze Cement

Repair casing leaks

• A packer is run and set above the damaged casing. • Cement slurry is circulated down to the damaged area• The packer is set• The cement slurry squeezed at low pressure in and around

the holes in the casing

Remedial squeeze techniques

PlacementLow-pressure squeeze

The injection of cement slurry into zones at pressures below the fracture pressure of the formation.

To fill perforation cavities or interconnected channels.

Slurry volumes are usually small since slurry is not injected into the formation.

Special precautions must be taken to ensure that the formation is not fractured.

High-pressure placement

Is used when it is not possible to inject slurry at pressures below the fracture pressure.

Cement is placed by breaking down the formation and injecting cement slurry into the zone.

Slurry volumes are usually relatively high since the created fractures and the perforations, have to be filled with cement slurry.

As a special precaution a wash or weak acid should be pumped ahead of the slurry to minimize the pump rates required to initiate the fractures.

Pumping

Running squeeze• The continuous pumping of a calculated volume of slurry until the final

squeeze pressure is attained.• This technique could be used during low-pressure or high-pressure

squeeze jobs but usually results in the pumping of large slurry volumes in such cases.

Time

Pressure

Hesitation squeeze

• The intermittent application of pressure at a rate of 0.25 bbl/min to 0.50 bbl/min at 10- to 20-min intervals until the final squeeze pressure is reached.

• Relatively small slurry volumes are used in hesitation jobs compared with those used in running squeeze jobs.• Hesitation time depends on the type of formation, ranging from 5 min in tight formations to 30 min in loose formations.

Pressure

ApplicationBradenhead squeeze

Sometimes referred to as the poor boy squeeze, does not use a downhole isolation tool.

The entire casing and wellhead is exposed to the final squeeze pressure.

When open perforations exist below the zone, it may be necessary to run a bridge plug to isolate it from the treated zone.

Applicable for shallow depths and long splits in casing

BOP

Cement

Bridge plug

Application• Squeeze tools

Uses either retrievable or drillable downhole tools.

Isolate the upper portion of the casing and wellhead from the cement and squeeze pressures and to improve the control and placement of fluids during squeeze cementing jobs.

Useful in multiple setting operations, such as selective testing and cementing of multiple zones.

Examples of the retrievable tools•DLT packer• PosiTrieve packer•Hurricane packer•Shorty squeeze tool•Retrievable bridge plug.

Plug Cementing

Side track and Directional DrillingPlug back and Depleted zonePrevent lost circulation zone (Thief Zone)Plugging abandonment wellProtect test anchor

Laboratory Testing, Evaluation & Analysis

of Well Cements

Introduction

• Laboratory Testing of cements and cementing materials is an essential part of the entire well cementing process• Testing begins at the manufacturing sites of the cement and additives

to monitor product quality• It continues through slurry design stages at pumping service company

or operating company laboratory as a specific formulation is developed

Two General Types of Testing Cements and Cementing Materials• Performance Evaluation• Chemical Characterization Performance Evaluation

• Typical oil field laboratory is engaged primarily in the performance evaluation of cements• This process involves physical measurement of specific slurry

properties under simulated downhole condition• This evaluation type is used mainly in the slurry design stages of

cementing treatment and in the execution stages to monitor the preparation of blended materials

Chemical Characterization

• It typically involves quantitative or qualitative analysis of slurry components prior to mixing• To ensure the suitability of use• Use for quality control purposes at the point of manufacture, to

determine all the components are in desired quantities and blended sufficiently

NoteCorrect application of a wide variety of laboratory testing method is necessary to achieve a successful cementing treatmentThis presentation only explains about broad overview of laboratory testing procedures and equipment

Performance Evaluation of Cement Slurries

• The standardized procedures for the performance evaluation is described in API spec 10

• The procedures are designed to simulate down-hole conditions for performance testing at field laboratory with compromise between realistic wellbore conditions and practical limitations of laboratory environment

Types of Performance Evaluation Tests• Slurry Preparation

• Thickening Time

• Fluid Loss

• Compressive Strength

• Free Water and Slurry Sedimentation

• Permeability

• Rheological Measurements

• Expansion

• Slurry Design

• Static Gel Strength

Slurry Preparation

• The equipment specs and operational procedures for the preparation of cement slurries for oil well in the lab are contained in Secton 5, Appendix A of API Spec • The mixing device is a two-speed propeller type mixer• Specification are given for the propeller speeds, mixing

blade wear, batch size and mixing time• Normally, 600mL of slurry are prepared• The mixer is operated at 4,000 rpm for 15 sec, followed by

35 sec at 12,000 rpm• Cement slurries are very abrasive, that means careful

monitoring of mixing blade condition is essential

Thickening Time

• Thickening time test are designed to determine the length of time which a cement slurry remains in a pumpable state under simulated conditions of temperature and pressure.• Section 8, appendix E of API spec 10• Pressurized consistometer, is primarily used for testing the

thickening time• A non-pressurized, or “Atmospheric Consistometer” is alsi used

for low-temperature cement, but its commonly used for conditioning of slurries (i.e. fluid loss, free water) before rheology• Most apparatus capable of temp and pressure ar 400 F and

25000 psi while some special apparatus are up to 600 F and 40000 psi for deep well application

Fluid Loss• Fluid loss tests are designed to measure the slurry dehydration

during and immediately following the completion phase of a cementing treatment• Operational test procedures are mentioned in Appendix F of API

Spec 10• After being subjected to the simulated well bore conditions in a

consistometer, the slurry is placed in heated filter press cell• The filterate loss either 100 psi or 1000 psi is measured acorss a

standardized filteration medium • All the filterate must pass through the screen in less than 30mins• F30= Ft 5.477/square roof of t• Ft is equal to the volume of filtrate(mL) collected at time t(min)

Compressive Strength

• Section 7, Appendix D of API Spec 10• Test cement slurries are poured into two-inches cube mold and

cured for various time periods at specific temperature and pressure• The set cement cubes are removed form the molds, placed in a

hydraulic press where increasing uniaxial pressure is exerted until failure• The compressive strength is calculated by dividing the pressure at

which failure occurred by cross-sectional area of that sample• A relatively recent development is estimation of compressive

strength by using Ultra Sonic Cement Analyser• Compressive strength are designed to furnish some indication of

the ability of a set cement to provide zonal isolation, to protect and support the pipe

UAC

Cement Mold and Hydraulic Press

Curing Chamber

Free Water and Slurry Determination• When a slurry is allowed to stand for a period of time prior to the set,

water may separated from the slurry, migrate upward and accumulate either in the pockets or at the top of the column

• This separation can result in incomplete zonal isolation, particularly in a highly deviated wellbore

• The free water test is designed to measure this separation tendency in the laboratory, using as 250 mL graduated cylinder as a simulated wellbore

• The duration of test is 2 hours as described in API Spec 10, Section 6, Appendix M

• As with free water development, when a slurry is alloews to stand for a period of time prior to development of a set, suspended solid may tend to separate from the slurry and settle down towards the bottom

• Especially in slurry contacting weighing agents• Such sedimentation can produce a change in slurry density, leading annular

invasion and possible loss of well control

Permeability

• Permeability of cement sheath is vital parameter with regard to zoal isolation• Water at differential pressure of 20 to 200 psi is forced

through the sample of set cement for 15 minutes, or unitl one millimetre has been accumulated in the measuring tube• Many laboratories today use a Hassler sleeve-type holder

and make measurement of permeability to air, methane or other gases using the newer instrumentation. • API Spec 10, Appendix G

Permeameter

Rheological Measurements

• Accurate prediction of friction pressure drops and slurry flow properties depends upon reliable laboratory measurements of rheological parameters• Two basic types of apparatus are used today for rheological

measurement : Capillary Pipe Rheometers and Coaxial Cylinder Rotational Viscometer• Apart from friction pressure and flow regime calculation,

laboratory measurements can provide information about other slurry characteristics

Expansion

• Set cement expansion can be measured using the procedures from ASTM specification C151• Placing the cement slurry into a bar type mold and curing

underwater at atmospheric pressure• The cement bar is removed from the mold when it is

sufficiently strong and the length is carefully measured, returned back to mold for further testing• Two major drawbacks are incapable to take zero reading

and there is no provision for effect of pressure studying• A new apparatus is then available for measuring in line

with simulation of well bore environment

Curing Sleeves