Casing String and Suspension

Copyright 2007, , All rights reserved

Casing String and Suspension

Overview

Copyright 2007, , All rights reserved 2

Casing

Casing String Types

The reasons for running and cementing casing:

– Isolate zones,

– Prevent mud contamination of fresh water aquifers,

– Support well head equipment and BOPs,

– Keep hole open

– Seal off lost circulation zones,

– Control inflow from the producing zone(s),


7” Production casing

Exploration well

5 casings

Development well

4 casings

30”

20”

13-3/8”

Intermediate

9-5/8”

Reservoir

Conductor

Surface casing

20”

13-3/8”

9-5/8”

Offset

data

Intermediate

Example of Casing Series


Casing (1)

Casing String Type: Drive Pipe

– Commonly pile driven or jetted to a shallow depth (e.g. 100 ft),

– 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


Casing (2)

Casing String Types: Conductor Pipe

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

It is the string on which Divertor or Bell nipple can be set,

It is cemented to surface or seabed. It supports the wellhead and subsequent casing strings 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).


Casing (3)

Casing String Types: 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).

Copyright 2007, , All rights reserved 7Conductor pipe Surface casing

Landing area for

intermediate casing

Base Plate

The casing head housing can be used in conjunction with a

base plate for more effective weight distribution.


Slip-on weld bottom

connection

Threaded bottom

connectionOR

Casing Head on Surface casing (Bottom

Connection)


Casing (4)

Casing String Types: Intermediate Casing

Separates hole into workable sections,

The number of intermediate strings set depends on:– Fracture Pressure 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, over-pressurized zones),

The casing is normally cemented in the previous shoe or to surface. (could be cemented in two stages),

Common sizes and depths:– 13 3/8”, 10 3/4”, 9 5/8”,

– 3000’ to 10,000’.


Unconsolidated

Swelling

Abrasive

Instability

Fractured

Unsealed fault

Overpressured

Salt layer

Hole problems


Conductor

Surface casing

Intermediate

casing

Landing area

Casing Hangers


Functions of casing hangers

1. Suspends intermediate or production casing string

2. Seals off the casing annulus

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


SLIPS

BOWL

ELASTOMER

SEAL ELEMENT

Slip type casing hanger

1. Wrap around casing slips with sealing capability

2. Seal energized by casing weight


Second element of the wellhead

Casing Head Spools


Functions of casing head spools

Seals off (packs off) around current (surface casing) string,

Provides support for next casing with hanger

– Provides support for well control equipment (BOP Stack)

– Sealing the well bore from the atmosphere

– Controlling access to the well bore :

• for pressure control

• fluid returns.


Casing series & casing heads / spools


Seals off (packs off)

designed to fit around OD

of current casing

Side outlets

threaded or

studded

Top connection

Landing area for

next Casing Hanger

Bottom connection compatible

with the top connection on the

previous casing head or spool

Description of a spool


Casing (5)

Casing String Types: Production Casing

Final string to be run for production or testing,

The primary purpose is to isolate the production zones thus

allowing proper control of the reservoir,

Cementing is very important to prevent communication in the

annulus,

Covers worn or damaged intermediate string,

Common sizes: 7”, 7 5/8”, & 9 5/8”.


Liners (1)

Purpose:

Mostly same as production casing,

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”.


Liners (2)

Production Liner:

Liner Hanger hangs off the liner

in the last casing.

Liner Lap is filled with cement

which provides a seal.

Some Liner Hangers are

equipped with a rubber seal

element,

Liner Hanger Packer Liner

Last casing

Liner

hanger

Liner Lap


Liners (3)

Production Liner:

Tie-Back:

– The integration of the liner with

casing from top of liner to

surface,

– To cover corroded casing or

damaged zone above liner,

– Sometimes cemented in place,

– Additional casing spool required

to suspend tie-back,

– This is often done if production

is still commercially viable.

TIE BACK

STINGER

WITH

SEALS

LINER

PBR


Casing and Liners

Casing String Types:

Drive Pipe,

Conductor Pipe,

Surface Casing,

Intermediate Casing,

Production Casing:

– Liner,

– Liner & Tieback

– Full string


Effects of tubing leak


13 3/8” at

2931 ft

9 5/8” at

5451 ft

Gas Sand

Shale

TOC 2610 ft

Top gas sand 2988 ft

EFFECTS:

prod csg collapse

frac of cement

A B

Source of pressure built-up:

•casing leak

•micro annuli in cement

•poor cementation

Effect of pressure in B or C annulus


Casing Design Considerations

The end product of well design and construction is a

pressure vessel capable of withstanding the expected

internal and external pressures and axial loading,

Casing loads:

– tension

– collapse

– burst


Casing design considerations

Tension:

– Where: highest at top joint

– Design: add bending forces, shock loads

Collapse:

– Where: bottom of string

– Design: empty casing, mud outside, mobile formations, no cement

Burst:

– Where: top of string

– Design: no cement, mud outside, gas filled casing

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Casing String and Suspension

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