casing and tubing slides

7/30/2019 Casing and Tubing Slides

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Robert Gordon University and Owen S. Jenkins Ltd. 2010

ENM201 Wells

Casing and Tubing

Prepared and presented by

Owen Jenkins.


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2 Robert Gordon University


Casing


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3 Robert Gordon University


Casing

Pipe usually made of steel

A type of OCTG Oil Country TubularGoods

Other types include

Tubing Line pipe and

Drill pipe

Held together with threaded couplings

Both standard and premium proprietary types

are available


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4 Robert Gordon University Robert Gordon University and Owen S. Jenkins Ltd. 2010

Casing

Commonly used specifications:

API Spec 5CT/ISO 11960API Spec 5CT/ISO 11960 Specification forCasing and Tubing, Petroleum and natural gas

industries Steel pipes for use as casing or tubing

for wells (includes Errata dated April 2006) 8th

Edition, July 2005 Up to 20 OD

ISO 13680:2008ISO 13680:2008 Petroleum and Natural GasIndustries - Corrosion-Resistant Alloy SeamlessTubes for Use as Casing, Tubing and Coupling Stock

- Technical Delivery Conditions. 2nd. Edition.

Up to 339.73 mm OD (=13 3/8)


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Functions of Casing

Prevent caving of the wellbore

Prevent formation breakdown from high mudweight

Isolate zones of abnormal pressure

Seal off lost circulation zones (thief zones) To provide a means of completing and

producing the well efficiently

Provide structural support for wellheads andblow-out prevention equipment


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DifferentCasing

Strings


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Casing Programmes

Casing: considerable part of the overall well cost (


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Cementing Casing

Inner Casing String

Outer Casing String

Cement Sheath

Cement being injected

Casing is cemented

in place to:- Seal the casing in

the wellbore

Ensure a competent

pressure control

system Provide structural

support for the

casing


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Types of Casing

Conductor (or stove pipe)

Surface Casing

Intermediate Casing

Production Casing

Liner

Getting

smaller


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Conductor Casing or Pipe

Conductor: the first casing string to be run Often driven into the formation using large hydraulic jack-

hammers or pile-drivers.

Consequently has the largest diameter

Protects seabed formations from washouts through

erosion Protects surface formations which may have low

frictional strength

Could be exceeded by hydrostatic pressure exerted by drillingfluid when drilling a deeper section of the wellbore

Provides a conduit for mud returns


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Surface Casing

The main functions are:-

To seal off any fresh water sands Provide structural support for the blow-out

preventer (BOP) and wellhead equipment

Where abnormal pressures are expected the

setting depth is important

If the casing is set too high the formationstrength at the shoe may be too low to handle a

kick when drilling the next section


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Intermediate Casing

Intermediate, or protection casing

Used to isolate any troublesome formations whichwould/could cause drilling problems in the wellbore e.g.

sloughing shale

lost circulation high pressure zones

Several strings of intermediate casing may be required Depending upon the number of problems encountered

If rock formations are stable, drilling can be undertaken forrelatively long periods of time prior to the setting of casing


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Intermediate Casing

The setting depth depends on a

knowledge of pore pressures and fracture

gradients

During drilling operations the mud weight

controls pore pressures, but must not

exceed the fracture strength of shallower,un-cased zones


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Pore Pressure

The pressure of fluids within the pores of a reservoir

(usually hydrostatic pressure) or the pressure exertedby a column of water from the formation's depth to sea

level

When impermeable rocks (such as shales) form as

sediments are compacted, their pore fluids cannot

always escape and must then support the total

overlying rock column, leading to anomalously high

formation pressures


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Pore Pressure and Pressure

Gradient

Diagram courtesy of Schlumberger


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Production Casing

Usually the last string of CASING to be

run in the wellboreMay run through the pay zone

(reservoir)May be set just above the pay zone

For an open hole completionOr

Reservoir may have a LINER set across it.


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Production Casing:

Purpose

To isolate the production interval fromother formations such as water bearingsands

To protect the completion tubing Through which the reservoir fluids will be

transported to the surface

Production casing should be thoroughlypressure tested.


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Production Casing:

Testing

Usually pressure tested to around60% of its specified burst (internal

yield) pressure

If casing withstands that pressure it is

expected to be capable of

withstanding higher pressures


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Liner

A liner is a string of casing which does not extend backto the surface.

It is run back inside the previous casing string to providesome overlap

May be used either as an intermediate or production

string Much cheaper than a full length casing string

If required, a tie back string can be run to extend theliner back to the wellhead

A liner is usually less than 5,000 feet long.

Overlap typically 200500 feet

Liner overlap (liner lap) must be gas tight


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Casing vs. Bit Size (illustrative)

CasingSize ~20 ~133/8 ~95/8 ~7 ~ 5

Bit Size

(Typical)

24 to

26

16 to

17121/4

83/8 to

97/8~ 6


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Casing Setting Depth

The initial selection based on anticipated porepressures and fracture gradients

PP - Pressures at which fluid will come out of the formation FG - Pressures at which pumped fluid will fracture the

formation.

Consider relevant offset data in the estimatingpore pressures and fracture gradients

Also effect of hole angle on offset fracture

gradient


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Casing Setting Depth

The total depth of the well, and hence the

setting depth of the production casing orliner, is driven by logging, testing, and

completion requirements.

The shoe must be set deep enough to givean adequate sump for logging, perforating,

and to enable testing of the reservoir fluids


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Selecting Casing Setting Depth


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1) Draw the mean pore

pressure gradient curve

along with the lithology,if available



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2) Draw the mud weight

curve. The mud weight

curve should include a

200 to 400 psi trip

margin



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3) Draw the predicted

fracture gradient curve



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4) To determine initial

estimates of casing

setting depths

First:

Enter the mud weight

curve at Point A

(Total Depth (TD))


S l i C i S i D h


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4.2) Move up to Point Bwhich determines the

initial estimated setting

depth for the

intermediate casing

(actually run it 300400feet deeper)


S l ti C i S tti D th


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4.3) Move across to

Point C which

identifies the mud

weight requirement

for that depth




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4.4) Move up to Point D

which determines the

preferred setting depth

for the surface casing/intermediate string




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4.5) Move across to Point

E to identify the mud

weight required at thatdepth




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4.6) Point E is the normal pressure range and

no further casing is required to withstand the

associated mud weight. However, a

structural and conductor casing arerequired, and the setting depth criteria for

those strings are discussed later


Other Factors Affecting


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g

Casing Programme

Ifshallow gas zones are encountered whilst drilling,operations must stop and casing must be set

Iflost circulation zones are encountered: Drilling should stop

Mud returns should be checked

Lost Circulation Material (LCM) pumped downhole before themud is conditioned to a more suitable rheology

The zone will then need to be drilled before casing can be set

Formation stabili ty: if the formation is sensitive to themud weight over time, casing may have to be set

Other Factors


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Other Factors

Directional well profile:

Important to line out the well trajectorybefore setting casing

Attempt to achieve a consistent surveyahead of a tangent.

Long open hole sections may require

casing to reduce the risk of stuck pipe and

the level of torque

Other Factors


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Other Factors

Side-tracking requirements

As specified in the drilling programme.

For example: the 13-3/8 casing may be

set high enough to allow9-5/8 casing to be cut and pulled,

enabling a side-track in 12-1/4 hole

Other Factors


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Other Factors

Fresh water sands:

Need to protect drinking water, and not

contaminate it with drilling fluid.

Hole cleaning:

Particularly if a long section of 17-1/2 hole

is required.

Other Factors


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Other Factors

Salt sections

High pressure zones; Casing shoe should be set in competent

formations

Uncertainty in depth estimating

Require a margin related to confidence limit

when setting close to a permeable formation. Best source for this information is offset well

data or area experience, but this should be

documented


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Kick Tolerance

Once the initial casing setting depths are selected, the

kick tolerance associated with those depths should be

determined.

Start from TD up to the surface to determine the kick

tolerance and preferred setting depth for each casing

string.

The acceptability of kick tolerance values of less than

100 bbls should always be justified

By review of the type of well

Capacity of rig equipment for kick detection

Operator/Drillers experience, area experience and geology

Design Bottom-to-Top AND


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Top-to-Bottom

A design should be developed by well planning thatprovides for economic production from the pay zone

consistent with safety requirements. The pay zone should be analysed for its flow potential

and likely drilling problems.

The well should be designed initially from bottom-to-top. The opposite approach may result in a well that limits the

production capacity

Also necessary to work the other way around: it isessential to have a well design which is do-able withthe rigs and equipment available.


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Design of the Completion Tubing

Must be able to transport oil or gas to the surface at

economical rates.

Small diameter tubing tends to choke the flow rate due tohigh frictional pressures

Large diameter strings are usually preferable for good flow rate

BUT may be more prone to slugging depends upon GOR andnature of fluids

Small completion tubing can also lead to operational problems

due to reduced radial clearances

The completion design must be taken into account whendesigning the casing string

F th R di


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Further Reading

Bourgoyne, A.T., Jr., Chenevert, M.E., Millheim,

K.K., Young, F.S., Jr. 1986, Applied DrillingEngineering (Society of Petroleum Engineers)

Chapter 7 Casing Design

Devereux, S., 1998, Practical Well Planning andDrilling Manual (PennWell)

Chapter 1.4 Casing Design

Chapter 2.6 Casing Running Program

H l f l W b it


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Prepared byOWEN S. JENKINS LTD.4, Charlton Avenue, Aboyne, Aberdeenshire, AB34 5GL,

Scotland.

Tel. +44 (0)13398 87779. Mobile phone: +44 (0)7803 296779.

Email: [email protected]: www.osjl.co.uk

Acknowledgement: The foregoing slides were largely developed

from material supplied by colleagues at RGU.

ENM201 Wells

Casing and Tubing
mailto:[email protected]://www.osjl.co.uk/http://www.osjl.co.uk/mailto:[email protected]

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