csg type & design.ppt

Network of Excellence in Training

© COPYRIGHT 2001, NExT. All Rights Reserved

Casing, Casing Suspension& Casing Design

2© COPYRIGHT 2001, All Rights Reserved

Casing and Casing DesignCasing and Casing Design• Lecture Contents;

– Objectives,

– Casing String Types,

– Casing String Components,

– Casing Classification,

– Casing Handling,

– Casing Design Considerations.


Casing and Casing DesignCasing and Casing Design• Objectives;

– By the end of this lecture YOU will be able to:

• Identify basic functions of casing strings,

• Relate these functions to required characteristics for surface, intermediate and production casing strings,

• Describe the relative importance of casing dimensions and steel grade to ability to withstand various loads,

• Explain the importance of careful handling to casing,

• Understand basic casing design considerations.


Casing and Casing DesignCasing and Casing Design• Casing String Types;

– Introduction:

• At certain intervals during drilling of a well, casing (steel pipe) is run into the wellbore and cemented in place,

• The reasons for running casing include the following:

– Support wellhead equipment and BOPs,

– Prevent mud contamination of water table at surface,

– Control influx from formation fluid,

– Seal off lost circulation zones,

– Keep hole open,

– Isolate producing zone.


7” Production casing

Exploration well

5 casingsDevelopment well

4 casings

30”

20”

13-3/8” Intermediate


Reservoir

Conductor

Surface casing

20”

13-3/8”


Casing and Casing DesignCasing and Casing Design


• Casing String Types;

– Drive Pipe:

• This type is commonly pile driven or jetted to a depth of several tens of meters,

• The primary purpose is to protect unconsolidated surface soils from erosion,

• They are typically of large diameter (more than 20 inches),

• Joints are normally welded together, special couplings can be used depending on the circumstances.




– Conductor Pipe:

• This is the first casing to be run when there is no drive pipe to prevent washing out under the rig,

• Provides elevation for return flow to bell nipple,

• It is the string on which Diverter can be set,

• It is cemented to surface or seabed. It supports the wellhead and subsequent casing string and its setting is critical in terms of compressional loading and integrity of the cement,

• Common Sizes and Depths:

– 30” - 20” Welded, 20” - 16” Threaded,

– 30’ - 200’ (< 100’ common).




– Surface Casing:

• Protects fresh water aquifers,

• It is the first string on which BOP can be set to provide primary pressure control,

• It is cemented to surface or seabed, to case-off, unconsolidated or lost circulation areas and support subsequent casing strings/ wellhead,

• Common sizes and depth:

» 20”- 16” - 13 3/8”- 9 5/8” threaded,

» 100’ - 3000’ (or more).



Wellheads - Casing Head HousingWellheads - Casing Head Housing

Base PlateBase Plate

The casing head may be used in conjunction with a base plate for more effective weight distribution.

Conductor pipe Surface casing

Cellar deck

10 © COPYRIGHT 2001, All Rights Reserved

• It can be :

Cast or forged integrally with the casing head

or fabricated and attached to the casing head with welded gussets.


Base PlateBase Plate

Base Platewith welded gussets


Bottom ConnectionBottom Connection

Slip-on weld bottomconnection (standard)

Threaded bottomconnection



Type of OutletsType of Outlets

Threadedoutlet

Flangedoutlet

Clamp huboutlet

Studdedflangeoutlet



• Casing String Types;– Intermediate Casing:

• Separates hole into workable sections,

• The number of intermediate strings set depends on:

– Fracture Pressure/Kick tolerance at last shoe,

– Proximity to a potential reservoir. (It is good practice to set intermediate string above reservoir),

– Hole problems (i.e. lost circulation, salt section, differential sticking, caving, overpressured zones, heaving shale),

• The casing is normally cemented meters above the shoe or to surface. It could be cemented in two stages as well,

• Common sizes and depths:

– 13 3/8”, 10 3/4”, 9 5/8”,

– 3000’ to 10,000’.



WellheadsWellheads

Casing Head SpoolsCasing Head SpoolsSecond element of the Second element of the

wellheadwellhead


FunctionsFunctions1. Seals off (packs off) surface casing string

2. Provides support (landing bowl) for next casing string

provides support for well control equipment (BOP Stack)

Sealing the wellbore from the atmosphere

Controlling access to the wellbore : for pressure control or fluid returns during drilling operations.

Wellheads - Casing Head SpoolsWellheads - Casing Head Spools


DescriptionDescription

Seals off (packs off) designed to fit around OD of current casing

Test port

Side outlets threaded or studded

Top connection flanged (standard) or clamp hub Ring groove

Landing area forCasing Hanger

Wellheads - Casing Head SpoolsWellheads - Casing Head Spools

Bottom connection compatible with the top connection on the previous casing head or spool


Casing HangersCasing HangersWellheads Wellheads

Conductorpipe

Surface casing

Intermediatecasing

Landing area


FunctionsFunctionsWellheads - Casing HangersWellheads - Casing Hangers

1. Suspends intermediate or production casing string

2. Centres the casing string in the head (or spool)

3. Seals off the casing annulus


Two major types of casing hangers :

1. Slip type hanger (wraparound casing slips)

2. Mandrel type hanger

TypesTypesWellheads - Casing HangersWellheads - Casing Hangers


SLIPS

BOWL

ELASTOMERSEAL ELEMENT

Slip type hangersSlip type hangersWellheads - Casing Hangers - Wellheads - Casing Hangers - TypesTypes

1. Wraparound casing slips with sealing capability

FMC - C22


Cameron Casing Hanger SB5

SEAL PLATESEAL

SLIP

SLIPBOWL

Slip type hangersSlip type hangersWellheads - Casing Hangers - Wellheads - Casing Hangers - TypesTypes

1. Wraparound casing slips with sealing capability


Annulus sealing with the casing hanger

Isolation of AnnulusIsolation of AnnulusWellheads - Isolation Seals and Pack offWellheads - Isolation Seals and Pack off


Isolation Seals and Pack OffIsolation Seals and Pack OffWellheadsWellheads

Prevents communication :

• between the casing strings

• and exposure of the flange seal to annulus pressure.


Isolation SealsIsolation SealsWellheads - Isolation Seals and Pack offWellheads - Isolation Seals and Pack off

Interface seal rings

Nonextrusionrings

FMC Seal Rings

Test Port


Wellheads - Isolation Seals and Pack offWellheads - Isolation Seals and Pack off

Check valve

Elastomer rings

Nonextrusionrings

Injection plug

Port threaded for injection plug

Port plug

FMC Elastomer Seal Rings

Isolation SealsIsolation Seals



– Production Casing:

• Final string to be run in which production testing and subsequent production will take place,

• The primary purpose is to isolate the production zones thus allowing proper control of the reservoir (artificial lift, multiple zone completion etc.),

• It can be full string from surface, a liner hung from the last intermediate casing or a liner that is tied back to the surface,

• Cementing is very important to prevent communication in the annulus,

• Covers worn or damaged intermediate string,

• Common sizes: 7”, & 9 5/8”.



Casing and Casing DesignCasing and Casing Design• Types of Casing;

– Liners;

• Purpose:

– Mostly same as production casing,

– Cover Lost circulation zones, shale or plastic formations, and salt zones.

– Rig unable to lift long string of casing in Deep Wells,

• Types of Liners

– Production Liners: Most common to save $$,

– Drilling Liners: Cover problem zone or cover worn-out casing in order to be able to continue drilling,

• Common sizes: 4 1/2”, 5”, 7”.


• Casing String Types; – Production Liner:

• Tie-Back (Liner Complement):

– The integration of the liner with casing from top of existing liner to surface,

– To further up casing to cover corroded or damaged zone,

– This is often done if production is commercially viable or there is damage to casing above the liner.


TIE BACK

STINGER WITHSEALS

LINER



– To Conclude;

• Drive Pipe,

• Conductor Pipe,

• Surface Casing,

• Intermediate Casing,

• Production Casing:

– Liner,


• Liner & Tieback,

• Full String.


Casing and Casing DesignCasing and Casing Design• Casing Classifications;

– Outside Diameter:

• This is the normal (nominal) diameter of the casing measured to the outside surface of the casing body,

• API permits a tolerance of + 0.75%.

– Weight:

• It is the weight of the finished joint including couplings and upsets where appropriate per unit length,

• The nominal weight of the casing is expressed in either pounds per foot or kilograms per meter.


• Casing Classifications;

– Wall Thickness:

• It is half of the difference between the nominal outside and inside diameters of the casing body with a tolerance of

-12.5%, and related to weight and wall thickness,

• The drift diameter is used in sizing the drill bit.

– Grade:

• The grade of a casing is designated by a letter and number combination (e.g. J55, C75, N80, P110),

• The number is the API minimum internal yield strength in thousands of psi,

• Hence, for example, J55 has a minimum yield strength of 55000 psi.



Casing and Casing DesignCasing and Casing Design• Casing Handling;

– Casing is very susceptible to damage, particularly on the pin end,

– All casing delivered to a rig site should be fully inspected for defects,

– It should be checked to ensure that all thread protectors are on, hand-tight and that all pins and boxes be doped to attachment of the protectors,

– It should be lifted onto the rig floor with the protector on pin end.


• Casing Handling;

– Only approved casing dope should be used at the tool joint,

– Torque limits vary for particular casing size and grade. If the make-up toque is too low , there is a possibility that the casing will leak or part,

– Buttress threads have a triangle on its body, this will guide the operator to figure out the maximum make-up torque,

– In some special casing like VAM-ACE and New-VAM, specialized equipment (e.g. Weatherford JAM system) to be used to accurately measure the torque per joint.



Casing and Casing DesignCasing and Casing Design• Casing Design Considerations;

– Definition:

• Casing design involves the determination of factors which influence the failure and the selection of the most suitable casing grades and weights for specific operations,

• The casing program should also reflect the completion and production requirements,

• A good knowledge of the stress analysis and the ability to apply it are necessary for the design of casing strings.


• Casing Design Considerations;

– Definition:

• The end product of such design is a pressure vessel capable of withstanding the expected internal and external pressures and axial loading,

• Hole irregularities further subject the casing to bending forces which must be considered during the selection of casing grades,

• In general, the cost of a given casing grade is proportional to its weight, the heaviest weight being the most expensive,

• And hence the designer must ensure the cheapest without compromising the safety and quality.




– Design Criteria;

• Main casing design criteria are:

– Collapse,

– Burst,

– Tension.




– Design Criteria:

• Collapse Pressure:

– This pressure originates from the column of mud used to drill the hole and acts on the outside of the casing,

– Since the hydrostatic pressure of a column of mud increases with depth collapse pressure is highest at the bottom and zero at top.


Pressure Pressure




• Basic Collapse Assumptions:

– Casing is empty due to lost circulation

at shoe or at TD,

– Internal pressure inside casing is zero,

– External pressure is caused by mud in

which casing was run,

– No cement outside casing.


CSD

TD




• Burst Pressure:

– The burst criterion is normally based on the maximum formation pressure resulting from a kick during the drilling of the next hole section.


Pressure




• Burst Pressure:

– Gas to Surface:

» This is an extreme case,

» For added safety it is assumed that the influx fluid displaces the entire drilling mud,

» This will subject the inside casing to bursting effects of formation pressure.


CSD

TD




• Burst Pressure:

– Gas to Surface:

» At the top of the hole, the external pressure due to hydrostatic head of mud is zero and the internal pressure must be supported entirely by the casing body,

» Therefore, the burst pressure is highest at the top and lowest at the casing shoe where internal pressure is resisted by the external pressure due to fluids outside the casing,

» In conventional casing design, it is customary to assume a gas kick, thereby anticipating the worst possible type of a kick.





• Burst Pressure:

– Gas to Surface:

» The gas gradient is in the order of 0.1 psi/ft. This gradient causes a small decrease in formation pressure as gas rises up the well,

» Casing seat should be selected so that gas pressure at the casing shoe is less than the formation breakdown at the shoe,

» In exploration wells, where reservoir pressure is not known, formation pressure from the next openhole section is calculated from the maximum mud weight.





• Tension:

– Most of axial tension arises from the weight of the casing itself,

– Other tension loadings can arise due to:

» Bending,

» Drag,

» Shock loading and during pressure testing of casing.

– In casing design, the uppermost joint of the string is considered the weakest in tension as it has to carry the total weight of the casing string.



Casing and Casing DesignCasing and Casing Design• Now YOU should be able to:

– Identify basic functions of casing strings,

– Relate these functions to required characteristics for surface, intermediate and production casing strings,

– Describe the relative importance of casing dimensions and steel grade to ability to withstand various loads,

– Explain the importance of careful handling to casing,

– Understand basic casing design considerations.

csg type & design.ppt

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