API Introduction Standards

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Casing Design

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

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

Casing Design

Introduction



Component Parts of A Casing String

Casing Components



• 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.

Conductor Casing

Casing Components



• 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 fulllength. Surface casing supports the BOP stack and

subsequent casing and tubing strings, and is normally

the only string designed to carry compression loads.

Casing Components

Surface 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.

Intermediate Casing

Casing Components



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.

Production Casing

Casing Components



Running Casing

Casing Components



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.

Running Casing

Casing Components



Casing Design

Bit – Hole - Casing



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.

API Standard

API Standard



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.

Casing Length

API Standard



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.)

Casing Weight

API Standard



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.

Casing Grade

API Standard



Typical yield behavior for non-ferrous alloys.

1: True elastic limit

2: Proportionality limit

3: Elastic limit

4: Offset 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.

Definition of Yield Strength

API Standard



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.

Casing Grade

API Standard



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)

Connections

API Standard



Connections

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 drillpipe”: Provides a uniform method of inspecting tubular goods.

API Standard




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.

API Standard




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.

API Standard



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.

Rig-Site Operation




Rig-Site Operation




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. Arunning 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.

Rig-Site Operation




Rig-Site Operation

Regular Slip

Heavy duty slip



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.

Rig-Site Operation




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.

Rig-Site Operation




Rig-Site Operation

API Introduction Standards

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