Well Design

1

• Well Design
• PE 413
• Introduction and API Standards of Casing

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Casing Design
Introduction

• Choosing the correct size, type, and amount of
  casing that is used in well construction is of
  utmost importance to the success of the well. The
  casing must be of sufficient size and strength to
  allow the target formations to be reached and
  produced.
• Casing has become one of the most expensive parts
  of a drilling program the average cost of
  tubulars is about 18 of the average cost of a
  completed well. Thus, an important responsibility
  of the drilling engineer is to design the least
  expensive casing program that will allow the well
  to be drilled and operated safely throughout its
  life

3
Casing Design
Introduction

• The main functions of the casing in any well are
  
• Maintain hole integrity
• Isolate abnormally pressured zones
• Protect shallow weak formations from heavier mud
  weights required in the deeper portions of the
  hole
• Prevent contamination of freshwater-bearing
  strata
• Support unconsolidated sediments

4
Casing Components
Component Parts of A Casing String
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Casing Components
Conductor Casing

• Sea off unconsolidated formations at shallow
  depths
• Stop washouts under the drilling rig.
• Protect fresh water sands.
• To give a base and support for the next string
  of casing
• The conductor pipe is the first casing to be put
  in place, and is generally installed before the
  rig arrives on location. Such casing can be
  driven to 250 feet. Conductor casing measuring
  between 16 to 24" outside diameter is used
  onshore, and between 24 to 48" for offshore.

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Casing Components
Surface Casing

• Protect, water sands
• Support the wellhead and BOP equipments
• Case unconsolidated formations
• Support other casings
• Case off lost circulation zones
• Surface casing is the first string of casing used
  after the conductor pipe. It is required in some
  instances by law (to protect ground water) and is
  normally cemented full length. Surface casing
  supports the BOP stack and subsequent casing and
  tubing strings, and is normally the only string
  designed to carry compression loads.

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Casing Components
Intermediate Casing

• Intermediate casing is any string between the
  surface and production string. Intermediate
  casing may or may not be cemented full length.
• Intermediate casing may be used to
• Seal off weaker zones
• Protect previous casing strings from higher
  Pburst
• Provide support for liner casing.

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Casing Components
Production Casing
The fourth but not necessarily the final string
of pipe run in the hole is the production casing.
The production casing is used to control the
hydrocarbon bearing zones that will be produced.
This string of pipe adds structural integrity to
the wellbore in the producing zones. Production
casing should be set before completing the well
for production. It should be cemented in a manner
necessary to cover or isolate all zones which
contain hydrocarbons.
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Casing Components
Running Casing
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Casing Components
Running Casing

• Mississippi Not encounter abnormal formation
  pressure, lost circulation zones, salt sections.
  Required only conductor casing, surface casing
  and production casing
• Offshore Louisiana and Texas Delaware Basin
  Encounter abnormal pore pressure, lost
  circulation zones, salt sections, unstable shale
  sections. Required intermediate casing to protect
  formation below the surface casing from the
  pressures created by the required high drilling
  fluid density. Liner is used to lower the cost of
  drilling. It serves similarly to intermediate
  casing in that it isolates troublesome zones that
  tend to cause well problems during drilling
  operations.

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Casing Design
Bit Hole - Casing
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API Standard
API Standard
The size of the casing refers to the outside
diameter (O.D.) of the main body of the tubular
(not the connector). Casing sizes vary from 4.5"
to 36" diameter. Tubulars with an O.D. of less
than 4.5 are called Tubing.
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API Standard
Casing Length
The API standards recognize three length ranges
for casing Range 1 (R-1) 16 25 ft Range 2
(R-2) 25 34 ft Range 3 (R-3) gt 34 ft Casing
is run most often in R-3 lengths to reduce the
number of connections in the string. Since casing
is made up in single joints, R-3 lengths can be
handled easily by most rigs.
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API Standard
Casing Weight
For each casing size there are a range of casing
weights available. The weight of the casing is in
fact the weight per foot of the casing and is a
representation of the wall thickness of the pipe.
There are for instance four different weights of
9 5/8" casing. (Drift diameter refers to the
guaranteed minimum ID of the casing.)
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API Standard
Casing Grade

• In addition to the API grades, certain
  manufacturers produce their own grades of
  material. Both seamless and welded tubulars are
  used as casing although seamless casing is the
  most common type of casing and only H and J
  grades are welded.

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API Standard
Definition of Yield Strength
Proportionality limit Up to this amount of
stress, stress is proportional to strain (Hookes
law), so the stress-strain graph is a straight
line, and the gradient will be equal to the
elastic modulus of the material. Elastic limit
(yield strength) Beyond the elastic limit,
permanent deformation will occur. The lowest
stress at which permanent deformation can be
measured is defined as yield strength.
Typical yield behavior for non-ferrous alloys.1
True elastic limit2 Proportionality limit3
Elastic limit4 Offset yield strength
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API Standard
Casing Grade
The chemical composition of casing varies widely,
and a variety of compositions and treatment
processes are used during the manufacturing
process This means that the physical properties
of the steel varies widely. The materials which
result from the manufacturing process have been
classified by the API into a series of grades.
Each grade is designated by a letter, and a
number. The letter refers to the chemical
composition of the material and the number refers
to the minimum yield strength of the material
e.g. N-80 casing has a minimum yield strength of
80000 psi and K-55 has a minimum yield strength
of 55000 psi. Hence the grade of the casing
provides an indication of the strength of the
casing. The higher the grade, the higher the
strength of the casing.
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API Standard
Connections
Individual joints of casing are connected
together by a threaded connection. These
connections are variously classified as API
premium gastight and metal-tometal seal. In the
case of API connections, the casing joints are
threaded externally at either end and each joint
is connected to the next joint by a coupling
which is threaded internally. The standard types
of API threaded and coupled connection are
Short thread connection (STC) Long thread
connection (LTC) Buttress thread connection
(BTC)
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API Standard
Connections
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API Standard
API Specifications, Standard and Bulletins
API SPEC 5CT, Specification for casing a
tubing Covers seamless and welded casing and
tubing, couplings, pup joints and connectors in
all grades. Processes of manufacture, chemical
and mechanical property requirements, methods of
test and dimensions are included. API STD 5B,
Specification for threading, gauging, and thread
inspection for casing, tubing, and line pipe
threads Covers dimensional requirements on
threads and thread gauges, stipulations on
gauging practice, gauge specifications and
certifications, as well as instruments and
methods for the inspection of threads of
round-thread casing and tubing, buttress thread
casing, and extreme-line casing and drill
pipe. API RP 5A5, Recommended practice for filed
inspection of new casing, tubing and plain-end
drill pipe Provides a uniform method of
inspecting tubular goods.
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API Standard
API Specifications, Standard and Bulletins
API RP 5B1, Recommended practice for thread
inspection on casing, tubing and line pipe The
purpose of this recommended practice is to
provide guidance and instructions on the correct
use of thread inspection techniques and
equipment. API RP 5C1, Recommended practice for
care and use of casing and tubing covers use,
transportation, storage, handling, and
reconditioning of casing and tubing. API RP5C5,
Recommended practice for evaluation procedures
for casing and tubing connections Describes
tests to be performed to determine the galling
tendency, sealing performance and structural
integrity of tubular connections. API BULL 5A2,
Bulletin on thread compounds Provides material
requirements and performance tests for two grades
of thread compound for use on oil-field tubular
goods.
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API Standard
API Specifications, Standard and Bulletins
API BULL 5C2, Bulletin on performance properties
of casing and tubing Covers collapsing
pressures, internal yield pressures and joint
strengths of casing and tubing and minimum yield
load for drill pipe. API BULL 5C3, Bulletin on
formulas and calculations for casing, tubing,
drillpipe and line pipe properties Provides
formulas used in the calculations of various pipe
properties, also background information regarding
their development and use. API BULL 5C4,
Bulletin on round thread casing joint strength
with combined internal pressure and bending.
Provides joint strength of round thread casing
when subject to combined bending and internal
pressure.
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Rig-Site Operation
Casing Running Procedures
Casing leaks are often caused by damaging the
threads while handling and running the casing on
the rig. It has also been known for a joint of
the wrong weight or grade of casing to be run in
the wrong place, thus creating a weak spot in the
string. Such mistakes are usually very expensive
to repair, both in terms of rig time and
materials. It is important, therefore, to use the
correct procedures when running the casing.
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Rig-Site Operation
Casing Running Procedures
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Rig-Site Operation
Casing Running Procedures
As more joints are added to the string the
increased weight may require the use of heavy
duty slips (spider) and elevators If the casing
is run too quickly into the hole, surge pressures
may be generated below the casing in the open
hole, increasing the risk of formation fracture.
A running speed of 1000 ft per hour is often used
in open hole sections. If the casing is run with
a float shoe the casing should be filled up
regularly as it is run, or the casing will become
buoyant and may even collapse, under the pressure
from the mud in the hole. The casing shoe is
usually set 10-30 ft off bottom.
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Rig-Site Operation
Casing Running Procedures
Regular Slip
Heavy duty slip
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Rig-Site Operation
Liner Running Procedures
Liners are run on drillpipe with special tools
which allow the liner to be run, set and cemented
all in one trip. The liner hanger is installed at
the top of the liner. The hanger has wedge slips
which can be set against the inside of the
previous string. The slips can be set
mechanically (rotating the drillpipe) or
hydraulically (differential pressure). A liner
packer may be used at the top of the liner to
seal off the annulus after the liner has been
cemented.
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Rig-Site Operation
Liner Running Procedures
The basic liner running procedure is as
follows (a) Run the liner on drillpipe to the
required depth (b) Set the liner hanger (c)
Circulate drilling fluid to clean out the
liner (d) Back off (disconnect) the liner hanger
setting tool (e) Pump down and displace the
cement (f) Set the liner packer (g) Pick up the
setting tool, reverse circulate to clean out
cement and pull out of hole.
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Rig-Site Operation
Liner Running Procedures