Casing/Tubing design manual october 2005 Chevron

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(B-6)

is tube outside diameter

is tube wall thickness

Provided the tubular cross section and the internal and external fluids do not

change between the point of interest and the neutral point (

0), the curvature

will vary linearly.

B.6.2.2 Inputting a Trajectory Based on Helical Buckling

Depending on the software used for wear prediction, generating a trajectory for

the wear analysis may be either tedious or relatively easy.

• If the software only accepts a wellbore trajectory, then it is necessary to

generate a number of survey stations to describe the helical nature of the

buckled tube. Here it will be important to include sufficient points to

model the continuous azimuth change of the helix, with at least four

points per pitch as an absolute minimum. This latter restriction is

because of the inability of the more popular survey calculation methods

(minimum curvature, radius of curvature) to adequately handle azimuth

change in near vertical wellbores.

• If the software accepts, as an overlay on an existing survey, user

specification of a dogleg severity, then the task of describing a buckled

string is significantly easier. Given the curvature at the point of maximum

buckling (usually the cement top) and the location of the neutral point,

the buckling may be adequately described by inputting a series (ten

points should be sufficient) of dogleg severities between the maximum

curvature and the neutral point. One limitation of this method is that the

dogleg inserted by the software may be an inclination dogleg, rather than

the mixed inclination/azimuth dogleg characteristic of a helically buckled

tube.

The only software currently used in the industry for wear prediction is Maurer's

CWEAR series. Fortunately, CWEAR does allow the overlay of dogleg severities,

so that the method shown in the last bullet above can be used to generate a

trajectory for casing buckle.

Casing/Tubing Design Manual B-19

October 2005

Tubing and Critical Well Casing

Design Software

C.1 Introduction ..................................................................................................................... C-1

C.2 WELLCAT

™

..................................................................................................................... C-1

C.2.1 What WELLCAT

™

Will Do........................................................................................... C-1

C.1 Introduction

Tubing design, and casing design for critical well conditions (deep water, steam

injection, HPHT, etc.), involves substantial calculations on tubular temperature,

annulus pressure, tubular stresses, and tubing movement that offer ample

opportunity for human error. A recommended alternative to hand calculations is

to use a qualified casing and tubing design computer program. The

recommended tool for such tubular design calculations is WELLCAT™, a well

casing and tubing product marketed by Landmark

Formal instruction in the use of WELLCAT™, including user manuals, is available

through the normal company educational channels. This training is a prerequisite

to gaining full benefit from the material to follow. This discussion is intended as a

supplement to the WELLCAT™

user manuals and has as its purpose to:

• Link the use and understanding of WELLCAT™

to the design principles

and equations presented in this text.

• Document the internal assumptions in WELLCAT™

for company and

regulatory audits.

C.2 WELLCAT

™

The following material supplements, but is not a replacement for, the extensive

help accompanying the WELLCAT™

software.

C.2.1 What WELLCAT

™

Will Do

WELLCAT™ is an integrated suite of programs that predicts temperatures and

pressures in the wellbore and analyzes stresses and deformation (including

buckling) in tubing and casing.

WELLCAT™ makes it possible for you to perform the following essential tasks:

• Model accurate temperatures (drilling and production)

• Analyze reliable service life

• Conduct critical well design

Enertech, 5847 San Felipe, Suite 1000, Houston, Texas 77057. Telephone (713) 789-

0055. Fax (713) 789-7633. Internet enertech@halnet.com. Enertech is a subsidiary of

Halliburton.

Casing/Tubing Design Manual C-1

October 2005

• Analyze complex tubular stress and movement

• Perform multi-string analysis

The illustration below shows the interrelationship between the applications in the

WELLCAT™ system. The arrows indicate that the results from one module that

can be input into another.

Figure C-1. The Interrelationship between Applications in the WELLCAT™ System

Module Drill is used to simulate fluid flow and heat transfer during drilling

operations. It has full transient analysis, linked analysis with Casing, and is an

advanced Windows

-environment engineering tool for predicting:

• Cementing temperatures

• HPHT hydraulics

• Downhole tool temperatures

• Casing service loads during drilling

• Undisturbed temperature profile from log data

Use Drill’s functional features to:

• Model the thermal disturbances due to drilling from the input of drilling

days, rotating hours, and average flow conditions

• Correct drilling fluid, cement rheology, and density for downhole

temperature and pressure

• Model for deviated and offshore wells

• Determine the undisturbed temperature profile from log data

• Determine the circulation temperatures, pressures, and effective

circulating densities for drilling, hole conditioning, and cementing

operations

• Model casing and liner cementing, cement squeezes, and cement plug

settings

C-2 Casing/Tubing Design Manual

October 2005

• Calculate slurry placement temperatures and temperature build up, start

to finish

• Determine post-cementing casing temperatures for landing and casing

temperatures during drilling of deeper intervals

Module Prod

is used to simulate fluid flow and heat transfer during

completion, production, simulation, testing, and well-servicing operations. It has

full transient (or steady-state) analysis with Tube and Casing, and is an

advanced Windows

-environment engineering tool for predicting:

• Temperatures and pressures for flowing and shut-in well-streams (see

Figure C-1)

• Conditions for tubing analysis based on service loads

• Temperatures and pressures during forward and reverse circulation

• Thermo-setting resin and gel treatment behavior

• Permafrost thaw radius

Casing/Tubing Design Manual C-3

October 2005

Figure C-2. Temperatures and Pressures Prediction for a Flowing Well Stream

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October 2005

Module Prod’s functional features allow you to:

• Model, in series of linked productions and non-production periods,

including circulation and injection operations, to build an accurate

chronology of wellbore thermal variations

• Model compositional (black-oil), VLE, and file-defined hydrocarbons, as

well as water-based and oil-based drilling fluids, brines, foams, cements,

and reactive gel treatment fluids

• Analyze multi-phase flow using standard industry correlations (Beggs &

Brill, Duns and Ros, Gray, Hagedorn & Brown, Orkiszewski)

• Analyze gas PVT behavior using standard industry equations-of-state

(Benedict-Webb-Rubin, Soave-Redlich-Kwong, Soave-Redlich-Kwong-

Starling, and Peng-Robinson)

• Model temperature and pressure dependences of density and viscosity

for water-based and oil-based drilling fluids

• Consider all casing strings and annulus fluids in thermal analysis, and

provision of temperatures at all significant radial positions

• Analyze of bottom hole pressure build-up behavior for shut-in gas wells

• Calculate time-domain variations of fluid pressure and properties in

transient analysis

• Analyze permafrost thaw and freezeback behavior

• Model gel-injection operations, with radial tracking of gel front in

permeable layers

• Analyze coiled tubing-aided well servicing operations

Module Casing

is used to analyze casing loads, design integrity, and

buckling behavior under complex mechanical, fluid pressure, and thermal loading

conditions. It has standard and automatic load-case generation, is linked to Drill

or Prod thermal analysis, and is an advanced Windows

-environment

engineering tool for:

• Comprehensive casing design and analysis (see Figure C-2)

• Installation and service load analysis

• Multi-string load transfer analysis

• Buckling stability and post-buckling analysis

With Casing you can:

• Determine running, installation, and service loads and stresses from

standard or automatically generated user-defined load cases

• Determine of accurate load, stress, and buckling solutions for both

vertical and directional wells, with or without friction

• Consider all mechanical, fluid pressure, and thermal loading

mechanisms

• Specify separate design factors for pipe body and connection

Casing/Tubing Design Manual C-5

October 2005

• Determine burst, collapse, axial, and triaxial safety factors, with burst and

axial safety factors based on lesser pipe body or connection ratings

• Accommodate user-specified yield anisotropy for CRA or composite

materials applications

• Accommodate user-specified temperature-dependant yield strength and

user-specified-minimum wall thickness (API default)

• Evaluate annulus fluid expansion due to heat up during drilling or

production, and determine the required bleed-off volumes for control of

collapse and burst loads

Figure C-3. Comprehensive Casing Design and Analysis

Module Tube is used to analyze tubing loads, design integrity, and

buckling behavior under complex mechanical, fluid pressure, and thermal loading

conditions. It has standard and automatic load-case generation, is linked to Prod

thermal analysis, and is an advanced Windows

-environment engineering tool

for:

• Comprehensive tubing design and analysis (see Figure C-3)

• Installation and service loads

• Tubing movement

• Complex completions

• Buckling

• CRA tubulars with yield anisotropy

• Tube has the following functional features:

• Determination of installation and service loads and stresses from

standard or automatically generated user-defined load cases, including

production, injection, shut-in, tubing leak, pump-in to kill, rod pump,

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October 2005

pressure test, fracture screen-out, full evacuation, and overpull during

installation

• Determination of accurate load, stress, and buckling solutions for vertical

and directional wells, with or without friction

• Accommodation of multiple mechanical or hydraulic-set packers and

dual-completion hook ups

• Specifications of latchdown and sliding tubing-packer seal assemblies,

with user-specified up/down displacement and no-go constraints

• Consideration of all mechanical, fluid pressure, and thermal loading

mechanisms for all load cases

• Specification of separate design factors for pipe body and connection

• Determination of burst, collapse, axial, and triaxial safety factors, with

burst and axial safety factors based on lesser of pipe body or connection

ratings

• Accommodation of user-specified yield anisotropy for CRA or composite

materials applications

• Accommodation of user-specified temperature-dependant yield strength

• Evaluations of annulus fluid expansion due to heat up during drilling or

production, and determination of required bleed-off volumes for control of

collapse and burst loads

Figure C-4. Comprehensive Tubing Design and Analysis

Module MultiString is used to conduct a total well system analysis. It can

also be used to analyze the influence of the thermal expansion of annulus fluids

(Fig. 9-4), and/or the influence of loads imparted on the wellhead during the life

of the well, on the integrity of a well’s tubulars. The single-string analyses

performed in Tube and Casing evaluates the effects of these loading conditions

Casing/Tubing Design Manual C-7

October 2005

on one string only. MultiString evaluates the effects of these loading conditions

on the entire load bearing strings in the well system. Either effect can be

modeled independently or the combined effects of both can be modeled.

The MultiString product requires data from each of the other four WELLCAT™

products (Casing, Tube, Drill, and Prod). Well configuration data, casing loads,

tubing loads, user inputs, and results from drilling and production thermal

analyses from Drill and Prod, respectively, are used to build a MultiString load

case. MultiString engineering code determines the pressures because of the

expansion of annular fluids, and the position (displacement) of the wellhead over

the life of the well. These pressure loads and wellhead displacement values are

used to determine the integrity of a well’s tubulars.

To correctly conduct a MultiString analysis, you first must correctly define the Drill

and Prod operations to establish the Casing and Tube initial and final

temperature conditions for each string. This is vitally important for the MultiString

analysis to be meaningful and correct.

Figure C-5. Thermal Expansion of Annulus Fluids

C-8 Casing/Tubing Design Manual

October 2005

DBasic Equations

D.1 Introduction ..................................................................................................................... D-2

D.2 Strain-Displacement Relations........................................................................................ D-2

D.2.1 Special Cases ............................................................................................................ D-5

D.2.1.1 Axisymmetric Deformation................................................................................ D-5

D.2.1.2 Plane Strain ...................................................................................................... D-6

D.2.2 Physical Interpretation of Strain Components ............................................................ D-6

D.3 Stress and Equilibrium .................................................................................................... D-9

D.3.1 Decomposition of the Stress Vector ........................................................................... D-9

D.3.2 The Equilibrium Equations........................................................................................ D-11

D.3.3 Special Cases .......................................................................................................... D-13

D.4 Stress-Strain Relations.................................................................................................. D-13

D.4.1 One-Dimensional Loading........................................................................................ D-14

D.4.2 American Petroleum Institute (API) Parameters....................................................... D-16

D.4.2.1 API Yield Stress.............................................................................................. D-16

D.4.2.2 Ultimate Stress and Elongation....................................................................... D-17

D.4.3 Needleman’s Model.................................................................................................. D-17

D.4.4 Ideal Plastic Behavior (Perfect Plasticity)................................................................. D-20

D.5 Multi-Dimensional Loading............................................................................................ D-21

D.5.1 Elastic Behavior........................................................................................................ D-22

D.5.2 Plastic Behavior........................................................................................................ D-23

D.5.3 Yield Condition ......................................................................................................... D-23

D.5.4 Hardening Law......................................................................................................... D-27

D.5.4.1 Residual Strain................................................................................................ D-27

D.5.4.2 Elastic Behavior.............................................................................................. D-27

D.5.4.3 Alteration of the Initial Yield Condition ............................................................ D-27

D.5.5 Flow Rule ................................................................................................................. D-29

D.5.6 The Effective Stress ................................................................................................. D-33

D.5.7 Elastic-Plastic Behavior............................................................................................ D-34

D.6 Loading and Deformation of a Thick Cylinder ............................................................... D-35

D.6.1 Elastic, Axisymmetric Deformation........................................................................... D-35

D.6.2 Initial Yield, Axisymmetric Deformation .................................................................... D-39

D.7 Approximations for a Thin Cylinder ............................................................................... D-41

D.7.1 Ignoring Radial Stress.............................................................................................. D-41

D.7.2 Using the Average Circumferential Stress................................................................ D-42

D.8 Changing Environmental Conditions............................................................................. D-45

D.8.1 General Comments .................................................................................................. D-45

D.8.2 Change In Length..................................................................................................... D-46

D.8.3 Tapered Strings........................................................................................................ D-47

D.8.4 Bending Stresses ..................................................................................................... D-48

D.9 References.................................................................................................................... D-51

Casing/Tubing Design Manual D-1

October 2005