Assoc. Prof. Issham Ismail

Faculty of Chemical & Energy Engineering,

Universiti Teknologi Malaysia,

Johor Bahru, Malaysia.

These presentation slides are strictly for domestic use.

CASING

WHAT IS CASING?

The first stage after the completion of

drilling phase is equipping the well with

casing!

DIFFERENCE BETWEEN

A CASING JOINT & TUBING JOINT

Steel pipe placed in an oil or gas well as

drilling progresses to prevent the wall of

the hole from caving in during drilling, to

prevent seepage of fluids, and to provide a

means of extracting petroleum if the well

is productive.

Casing(Definition)

To keep the hole open and to provide a support for weak or fractured formations.

To isolate porous media with different fluid/pressure regimes from contaminating the pay zone.

To prevent contamination of near-surface fresh water zone.

To provide a passage for hydrocarbon fluids.

To provide a suitable connection for BOP and well equipment.

To provide a hole of known diameter and depth.

Casing(Functions)

Drive pipe/stove pipe

Conductor casing

Surface casing (BOPs are connected to the top of it)

Intermediate casing

Production casing

Liner casing

Types of Casing

Marine conductor or foundation pile for offshore drilling.

To prevent washout of near-surface unconsolidated formations.

To provide a circulation system for the drilling mud.

To ensure stability of the ground surface upon which the rig is sited.

Does not carry wellhead equipment.

Driven into the ground with a pile driver.

Size ranging from 26 in to 42 in.

Stove Pipe

Installed from surface to some shallow depth to protect near-surface unconsolidated formations, and provide a circuit for the drilling mud.

Installed a diverter system or may be a BOP.

Cemented to the surface and used to support subsequent casing strings and wellhead equipment.

Sizes used: 18 5/8 in, 20 in, and 30 in

Conductor Pipe

Set in competent rocks to prevent caving of weak formations, protect against troublesome formations, water sand, etc.

BOPs are connected to the top of this string.

Cemented to the surface.

Sizes used: 18 5/8 in, 13 3/8 in, and 20 in.

Surface Casing

Set in the transition zone below or above an over-pressured

zone.

Used to seal off a severe-loss zone, or to protect against

salt sections or caving shales.

Cemented to the surface.

Sizes used: 9 5/8 in (depends on the tubing/production

casing size).

Intermediate Casing

Represents the last casing string.

Used to isolate producing zones, provide reservoir fluid

control, and to permit selective production in multizone

production.

The casing string thru which the well will be completed.

Cemented to 200 ft above the topmost HC zone.

Sizes used: 7 in (depends on the tubing/production casing

size).

Production Casing

Does not reach the surface – hung on the intermediate casing

using a suitable arrangement of a packer and slips called a

liner hanger.

Both liner and intermediate string act as the production string.

The advantages are reduce total costs and cementing time, and

the length of reduced diameter is reduced.

The disadvantages are possible leak across a liner and difficult

to get a primary cementation due to the narrow annulus

between the liner and the hole.

Liner Casing

Yield strength for pipe body and coupling – API defines as tensile

stress required to produce a total elongation of 0.5% of the gage length, as

determined by an extensometer.

Collapse strength – defined as the maximum external pressure required

to collapse a specimen of casing.

Burst strength for plain pipe and coupling – defined as the

maximum value of internal pressure required to cause the steel to yield.

Casing Strength Properties

Outside diameter and wall thickness – To cater for production requirements, and problems and pressures vary along any section of hole.

Weight per unit length – (1) Nominal Weight (identification during ordering), (2) Plain End Weight (without the inclusion of threads and couplings), (3) Threaded and Coupled Weight (average weight of a joint including the threads at both ends and a coupling at one end).

Type of coupling – (1) API 8 round thread, (2) Buttress thread, (3) Vam thread, (4) Extreme line threaded coupling, (5) Buttress double seal, etc. Please see next slide

Length of joint – Please see next slide.

Grade of steel – Please see next slide.

Casing Specification

Length of Joint

Range Length (ft) Average Length (ft)

1

2

3

16 – 25

25 – 34

Over 34

22

31

42

Grade of Steel

Grade Min Yield Strength (psi) Min Tensile Strength (psi)

H40

J55

K55

C-75

N-80

L-80

C-95

P110

40 000

55 000

55 000

75 000

80 000

80 000

95 000

110 000

60 000

70 000 – 95 000

70 000 – 95 000

95 000

100 000

100 000

105 000

125 000

1) If the maximum anticipated pressure is 17.2 ppg, next determine the total imposed pressure: 17.2 ppg (formation pressure – actual mud weight)

0.3 ppg (trip margin – actual mud weight)

0.3 ppg (surge pressure – equivalent mud weight)

0.2 ppg (safety margin – equivalent mud weight)Total 18.0 ppg

2) Determine those formation that cannot withstand a 18.0 ppg pressure.

3) The minimum depth found is 12,100 ft (refer to next 3 slides)

Setting Depth(Intermediate or deeper strings)

May use the following equation:

EMW = (Total depth/surface depth) (0.5) + Original mud weight

where

EMW = Equivalent mud weight at any depth, ppg

Total depth = Depth of deepest interval, ft

Surface depth = depth of interest, ft

(0.5) = Incremental mud weight increase, ppg

Original mud weight = Mud weight in use.

Setting Depth(Surface Casing)

Example:

An operator wishes to drill a well to 12,000 ft and use

sufficient surface casing so that an intermediate string is not

required. If the maximum anticipated mud weight at 12,000 ft

is 11.9 ppg, where must the surface casing be set? Use the

previously shown equation and the Eaton fracture gradient

chart.

Setting Depth(Surface Casing)

Eaton’s chart

Solution

1) Select a shallow depth and calculate the EMW and fracture gradient.

(a) EMW = (12,000 ft/1,800 ft) (0.5 ppg) + 11.9 ppg = 15.2 ppg

(b) From Eaton’s chart, the fracture gradient would be 12.7 ppg if

normal formation pressures are assumed.

2) Since the EMW exceeds the fracture gradient, a deeper interval must be evaluated. Sampel results are as follows:

Depth (ft) EMW (ppg) Fracture gradient (ppg)

1,800 15.2 12.7

2,400 14.4 13.3

2,700 14.1 13.5

3,000 13.9 13.7

3,300 13.7 13.8

3,500 13.6 14.0

3) A depth of 3,300 – 3,600 ft would be selected as the surface casing setting depth.

Setting Depth(Surface Casing)

Design criteria:

Tensile force (safety factor 1.6 – 1.8)

Collapse pressure (0.85 – 1.125)

Burst pressure (1.0 – 1.1)

Casing Design

Casing on rack

Oilwell Tubing

Casing with Protector

Lifting Casing

Lifting-up a Casing

Casing to be lifted

to the rig floor

Making-up a Casing at the Rig Floor

Hydraulic casing tong

is used to make-up the

casing

Installing Casing

Derrickman is

connecting the

elevator to the top of

casing…lowers into

the hole

Bit Scratcher and

centraliser…do you

know their functions?

Installing Casing

Casing Accessories

Centralizer

Scratcher

Cementing & Casing accessories

THANK YOU

QUIZ

Explain briefly the three design criteria that

must be considered in casing design.

Explain briefly three general functions of a

casing string.