Well Design – Spring 2011
Well Design
PE 413
Introduction and API Standards of Casing
Prepared by: Tan Nguyen
Well Design – Spring 2011
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
Prepared by: Tan Nguyen
Well Design – Spring 2011
Casing Design
Introduction
The main functions of the casing in any well are:
1.Maintain hole integrity
2.Isolate abnormally pressured zones
3.Protect shallow weak formations from heavier mud weights required in the
deeper portions of the hole
4.Prevent contamination of freshwater-bearing strata
5.Support unconsolidated sediments
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Well Design – Spring 2011
Casing Components
Component Parts of A Casing String
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Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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:
1. Seal off weaker zones
2. Protect previous casing strings from higher Pburst
3. Provide support for liner casing.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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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Well Design – Spring 2011
Casing Components
Running Casing
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Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
Casing Design
Bit – Hole - Casing
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Well Design – Spring 2011
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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Well Design – Spring 2011
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): > 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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.)
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
API Standard
Definition of Yield Strength
Proportionality limit:
Up to this amount of stress, stress is proportional to strain
(Hooke’s 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 limit
2: Proportionality limit
3: Elastic limit
4: Offset yield strength
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Well Design – Spring 2011
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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Well Design – Spring 2011
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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Well Design – Spring 2011
API Standard
Connections
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Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
Rig-Site Operation
Casing Running Procedures
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
Rig-Site Operation
Casing Running Procedures
Regular Slip
Heavy duty slip
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Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
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.
Prepared by: Tan Nguyen
Well Design – Spring 2011
Rig-Site Operation
Liner Running Procedures
Prepared by: Tan Nguyen