intoduction to casing

8/2/2019 Intoduction to Casing

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BASIC INFORMATION ABOUT CASING:

MANUFACTURE OF CASING

CASING TYPESCASING SPECIFICTION

BASICS OF CASING DESIGN


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MANUFACTURE OF CASING

The three basic processes used in the manufacture of

casing include:

(1)the seamless process,

(2)Electric resistance welding

(3)Continuous Butt welding


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Seamless process

A billet is first pierced by a mandrel in a rotary piercing mill. The heated billet

is introduced into the mill, where it is gripped by two obliquely orientedrolls that rotate and advance the billet into a central piercing plug (Fig. 7.2a).

The pierced billet is processed through plug mills, where the wall thickness of

the tube is reduced by central plugs with two single-groove rolls (Fig. 7.2b).

Reelers similar in design to the piercing mills are then used to burnish thepipe surfaces and to form a more uniform wall thickness (Fig. 7.2c). Finally,

sizing mills similar in design to the plug mills produce the final uniform pipe

dimensions and roundness (Fig. 7.2d).


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Electric welding processes

Flat sheet stock is cut and formed, and the two edges are welded together,

without the addition of extraneous metal, to form the desired tube.The electric-resistance process continuously makes casing from coiled sheet

stock that is fed into the machine, formed, and welded by an electric arc. The

pipe leaving the machine is then cut to the desired lengths.


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Continuous Butt welding technique

processes a sheet by cutting it to the desired dimensions, simultaneously

forming the entire length to a tube, and flashing and pressing the twoedges together to make the weld.


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CASING TYPES

six basic types of casing string are available

1- Drive pipe

2- Conductor casing

3- Surface casing

4- Intermediate casing5- Production casing

6- Liners


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Drive pipe

Provides a means of nippling up diverters

Provides a mud return path

Prevents erosion of ground below rig

Conductor pipe

Same as Drive pipe

Supports the weight of subsequent casing stringsIsolates very weak formations

Surface casing

Provides a means of nippling up BOP

Provides a casing seat strong enough to safely close in a well after a kick.

Provides protection of fresh water sands

Provides wellbore stabilization


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Intermediate or protective casing

Usually set in the first abnormally pressured zone

Provides isolation of potentially troublesome zonesProvides integrity to withstand the high mud weights necessary to reach TD or

next csg seat

Production casing

Provides zonal isolation (prevents migration of water to producing zones,isolates different production zones)

Confines production to wellbore

Provides the environment to install subsurface completion equipment


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Liners

Drilling liners

Same as Intermediate or protective casingProduction liners

Same as production casing

Tieback liners

Tie back drilling or production liner to the surface. Converts liner to full stringof casing


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CASING SPECIFICATION

Casing is classified according to five properties:

1- Casing size

2- Steel grade

3- Casing Connections

4- Length ranges5- Wall thickness (unit weight)


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1- Casing OD

4 1/2" Casing OD 30"

Tubing OD < 4 1/2"

DRIFT DIAMETR:

-12.5%

Although there are strict tolerance on the dimensions of casing, set out by the API, the actual I.D of the casing will vary slightly in

the manufacturing process.

For this reason the drift diameter of casing is quoted in the specifications for all casing. The drift diameter refers to theguaranteed minimum I.D of casing OR the biggest diameter of tools which could be passed through pipes.


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LENGTH OF DRIFT MANDRIL:

))D.D

.

4 1/2OD8 5/8 MANDRILL LENGTH=6INCH

8 5/8 OD MANDRILL LENGTH=12INCH


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2- Steel grade

Each grade is designated by a letter and a number. The letterrefers to the chemical composition of the material,

e.g N-80 casing has a minimumyield strength of 80,000 Psi.


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The nominal size of casing is its OD. The strength of a given size casing is

controlled by the yield strength and wall thickness of the steel. Steel used in

casing is relatively mild and can be normalized with small amounts of

manganese to increase its strength. Strength can also be increased by a

quenching and tempering (Q & T) process, which is favored by most

manufacturers because of its lower cost.


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API CLASSIFIED GRADE OF CASING INTO 4 CATEGORISES:

GROUP1: (H-40,J-55,K-55, N80), SEAMLESS & ERW

GROUP2: (M-65,L-80, L-80-9CR,L-80-13CR,C-90,C-95,T-95), ONLY SEAMLESS

GROUP3: P110 , (SEAMLESS WITH HIGH STRENGTH)

GROUP4: Q-125 , (SEAMLESS & SPECIAL)


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3- Casing Connections

The standard types of API threaded and coupled connections are:

STC: Short Thread Connection. The STC thread profile is 8 round, 8rd, 8 thread / inch

Round Thread Connection

LTC: Long Thread Connection. LTC is similar but with a longer coupling.

BTC: Buttress Thread Connection. The Buttress thread profile has flat crests. 5 thread / inch

EL: Extreme Line: Extreme line is connection without coupling, the thread is directly mashined in one end of pipe.

Extreme line connections also have flat crest and 5 thread / inch.EL Connection is the only API Connection that has a metal to metal seal

Extreme line is a standard upset connection.

There are three main style of connections:

Conventional: where the seal is ensured by grease and metalic compound packed down into the root of the thread.

VAM: VAM is a connection that uses the buttress thread but has a metal to metal seal provided by shoulder shape.

Extreme Line: Extreme line is connection without coupling, the thread is directly mashined in one end of pipe.


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4- Length ranges

RANGE R1 R2 R3

LENGTH(FT) 16 - 25 25 - 34 34-48

AVAREGE LENGTH (FT) 22 31 42


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Classification of Casings according to Wall thickness or Weight

1. NOMINAL WEIGHT: Average weight of 1 ft of length of Casing

2. PLAIN END WEIGHT: weight of Casing body without Coupling

3. AVERAGE WEIGHT: Average weight of 1 ft of length of Casing with

Coupling


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Collapse

API design recommendations call for worst case, where there is no pressure

inside the casing, and we design for the maximum mud weight at the casingdepth. We also allow for the reduction of the collapse rating from the weight of

the casing hanging below the depth of interest.


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Collapse Pressure

The following factors are important:

The collapse pressure resistance of a pipe depends on the

axial stress.

Tension reduce collapse resistance.

Compression increase collapse resistance.


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Burst

(from internal pressure)

Internal Yield Pressure for pipe

Internal Yield Pressure for couplings

Internal pressure leak resistance


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Burst

Design for maximum pressure on the inside of the casing.

API design recommendations call for the worst case scenario, which is the

casing is empty, and no external pressure. The pressure to design for is the

estimated formation pressure at TD for production casing, or estimated

formation pressure at the next casing depth.


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Tension


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API recommendations call for worst case, where there is no buoyancy effect.Design is based on the weight of the entire casing string.

Tension


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Required

10,000 psi

100,000 lbf

10,000 psi

Design

11,250 psi

160,000 lbf

12,500 psi

API Design Factors (typical)

Collapse 1.125

Tension 1.6

Burst 1.25


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